BBC Science - Cells

Cells

All animals and plants are made of cells. Animal cells and plant cells have features in common, such as a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also have a cell wall, and often have chloroplasts and a permanent vacuole. Note that cells may be specialised to carry out a particular function.

Dissolved substances pass into and out of cells by diffusion. Water passes into and out of cells by osmosis.

Animal and plant cells

Function of cells which animal and plant cells have in common

part	function
nucleus	contains genetic material, which controls the activities of the cell
cytoplasm	most chemical processes take place here, controlled by enzymes
cell membrane	controls the movement of substances into and out of the cell
mitochondria	most energy is released by respiration here
ribosomes	protein synthesis happens here

Plant cells also have extra parts:

Extra parts of plant cells

part	function
cell wall	strengthens the cell
chloroplasts	contain chlorophyll, which absorbs light energy for photosynthesis
permanent vacuole	filled with cell sap to help keep the cell turgid [turgid: having turgor; enlarged and swollen with water ]

Make sure you can label diagrams of animal and plant cells, like these:

Generalised animal and plant cell

Specialised cells

Cells may be specialised for a particular function. Their structure will allow them to carry this function out. Here are some examples:

Examples of the functions of cells

Cell	Function	Adaption
Leaf cell	Absorbs light energy for photosynthesis	Packed with chloroplasts. Regular shaped, closely packed cells form a continuous layer for efficient absorption of sunlight.
Root hair cell	Absorbs water and mineral ions from the soil	Long 'finger-like' process with very thin wall, which gives a large surface area.
Sperm cell	Fertilises an egg cell - female gamete	The head contains genetic information and an enzyme to help penetrate the egg cell membrane. The middle section is packed with mitochondria for energy. The tail moves the sperm to the egg.
Red blood cells	Contain haemoglobin to carry oxygen to the cells.	Thin outer membrane to let oxygen diffuse through easily. Shape increases the surface area to allow more oxygen to be absorbed efficiently. No nucleus, so the whole cell is full of haemoglobin.

You are likely to be given information, perhaps in a diagram, to help you to explain the adaptations of a particular cell type to its function.

Diffusion

Dissolved substances have to pass through the cell membrane to get into or out of a cell. Diffusion is one of the processes that allows this to happen.

Diffusion [diffusion: The movement of particles (molecules or ions) from an area of higher concentration to an area of lower concentration ] occurs when particles spread. They move from a region where they are in high concentration to a region where they are in low concentration. Diffusion happens when the particles are free to move. This is true in gases and for particles dissolved in solutions. Particles diffuse down a concentration gradient, from an area of high concentration to an area of low concentration. This is how the smell of cooking travels around the house from the kitchen, for example.

Examples of diffusion

Two examples of diffusion down concentration gradients

location	particles move	from	to
gut	digested food products	gut cavity	blood in capillary of villus
lungs	oxygen	alveolar air space	blood circulating around the lungs

Remember, particles continue to move from a high to a low concentration while there is a concentration gradient [concentration gradient: A difference in concentration between two areas next to each other. Particles will move down the concentration gradient from an area of high concentration to an area of low concentration. ].

In the lungs, the blood will continue to take in oxygen from the alveolar air spaces provided the concentration of oxygen there is greater than in the blood. Oxygen diffuses across the alveolar walls into the blood, and the circulation takes the oxygen-rich blood away.

Osmosis

Water can move across cell membranes because of osmosis. For osmosis to happen you need:

• two solutions with different concentrations
• a partially permeable membrane to separate them

Partially permeable membranes let some substances pass through them, but not others. The animation shows an example of osmosis.

Osmosis is the movement of water from a less concentrated solution to a more concentrated solution through a partially permeable membrane.

This is shown in the animation above. Eventually the level on the more concentrated side of the membrane rises, while the one on the less concentrated side falls. When the concentration is the same on both sides of the membrane, the movement of water molecules will be the same in both directions. At this point, the net exchange of water is zero and there is no further change in the liquid levels.

Osmosis is important to plants. They gain water by osmosis through their roots. Water moves into plant cells by osmosis, making them turgid [turgid: having turgor; enlarged and swollen with water ] or stiff so they that able to hold the plant upright.

Project - Young Geneticist

Young Geneticist

Bread Making - The Science

Bread is the product of baking a mixture of flour, water, salt, yeast and other ingredients. The basic process involves mixing of ingredients until the flour is converted into a stiff paste or dough, followed by baking the dough into a loaf. Bread making involves the following basic steps:




To make good bread, dough made by any process must be extensible enough for it to relax and to expand while it is rising. A good dough is extensible if it will stretch out when pulled. It also must be elastic, that is, have the strength to hold the gases produced while rising, and stable enough to hold its shape and cell structure.

Two proteins present in flour (gliadin and glutenin) form gluten when mixed with water. It is gluten that gives dough these special properties. Gluten is essential for bread making and influences the mixing, kneading and baking properties of dough. When you first start to bake bread the mixing is important.

Mixing and its effectsMixing fulfils two functions: to evenly distribute the various ingredients and allow the development of a protein (gluten) network to give the best bread possible. Each dough has an optimum mixing time, depending on the flour, additives and mixing method used. Too much mixing produces a dough that is very extensible with reduced elastic properties. Undermixing will not fully develop the dough, which will not have the capability to retain gas, therefore the final loaf will lack volume and have poor appearance inside.

FermentationOnce the bread is mixed it is then left to ferment (rise). As fermentation takes place the dough slowly changes from a rough dense mass lacking extensibility and with poor gas holding properties, into a smooth, extensible dough with good gas holding properties. The yeast cells multiply, the formed gluten strands join together to form networks and alcohol and carbon dioxide are formed from the breakdown of carbohydrates (starch, sugars) that are found naturally in the flour. The yeast uses sugars in much the same way as we do, that it breaks sugar down into carbon dioxide and water. Enzymes present in yeast and flour speed up this reaction. When there is plenty of oxygen present the following reaction occurs:



The energy which is released is used by the yeast for growth and activity. In a bread dough where the oxygen supply is limited, the yeast can only partially break down the sugar. Alcohol and carbon dioxide are produced in this process known as alcoholic fermentation.



The carbon dioxide produced in these reactions causes the dough to rise and the alcohol produced mostly evaporates from the dough during the baking process. During fermentation each yeast cell forms a centre around which carbon dioxide bubbles form. Thousands of tiny bubbles, each surrounded by a thin film of gluten form cells inside the dough piece. The increase in dough size occurs as these cells fill with gas.

Kneading/MouldingAny large gas holes that may have formed during rising are released by kneading. A more even distribution of both gas bubbles and temperature also results. The dough is then allowed to rise again and is kneaded if required by the particular production process being used. During the final rising (proving) the dough again fills with more bubbles of gas, and once this has proceeded far enough the doughs are transferred to the oven for baking.

Dough Rising


General appearance - large gas holes lined with gluten with smaller holes and ingredients in between these.



After two hours rising gluten strands form a lattice as the dough reaches the required size.

BakingThe baking process transforms an unpalatable dough into a light, readily digestible, porous flavourful product. The physical activities involved in this conversion are complex but the fundamentals of these are explained.

As the intense oven heat penetrates the dough the gases inside the dough expand, rapidly increasing the size of the dough. This is called "ovenspring" and is caused by a series of reactions: Gas + heat = increased volume or increased pressure. Gas pressure inside the thousands of tiny gas cells increases with the heat and the cells become bigger.

A considerable portion of the carbon dioxide produced by the yeast is present in solution in the dough. As the dough temperature rises to about 40°C, carbon dioxide held in solution turns into a gas, and moves into existing gas cells. This expands those cells and overall the solubility of the gases is reduced. The oven heat changes liquids into gases by the process of evaporation and thus the alcohol produced evaporates. Heat also has an effect on the rate of yeast activity. As the temperature rises the rate of fermentation increases, and so does the production of gas cells, until the dough reaches the temperature at which yeast dies (approximately 46°C). From about 60°C onwards stabilisation of the crumb begins. Starch granules swell at about 60°C, and in the presence of water, released from the gluten, the outer wall of the starch granule cell bursts and the starch inside forms a thick gel-like paste, that helps form the structure of the dough. From 74°C upwards the gluten strands surrounding the individual gas cells are transformed into the semi-rigid structure commonly associated with bread crumb strength. The natural enzymes present in the dough die at different temperatures during baking. One important enzyme, Alpha-amylase, the enzyme which breaks starch into sugars, keeps on performing its job until the dough reaches about 75°C. During baking the yeast dies at 46°C, and so does not use the extra sugars produced between 46-75°C for food. These sugars are then available to sweeten the bread crumb and produce the attractive brown crust colour. As baking continues the internal loaf temperature increases to reach approximately 98°C. The loaf is not completely baked until this internal temperature is reached. Weight is lost by evaporation of moisture and alcohol from the crust and interior of the loaf. Steam is produced because the loaf surface reaches 100°C+. As the moisture is driven off, the crust heats up and eventually reaches the same temperature as the oven. Sugars and other products, some formed by breakdown of some of the proteins present, blend to form the attractive colour of the crust. These are known as "browning" reactions, and occur at a very fast rate above 160°C. They are the principal causes of the crust colour formation.

CoolingIn bakeries bread is cooled quickly when it leaves the oven. The crust temperature is over 200°C and the internal temperature of the crumb about 98°C. The loaf is full of saturated steam which also must be given time to evaporate. The whole loaf is cooled to about 35°C before slicing and wrapping can occur without damaging the loaf.

A moist substance like bread loses heat through evaporation of water from its surface. The rate of evaporation is affected by air temperature and the movement of cool air around the loaf.

In a bakery there are special cooling areas to ensure efficient cooling takes place before the bread is sliced and wrapped.

Yeast Bread Ingredients

There are only four ingredients you need to make yeast bread: flour, yeast, water, and salt. All other ingredients are there to add flavor, nutrition, color, and to change the characteristics of the crumb. Here's what yeast bread ingredients do:

Flour
Flour provides the structure for the product. The gluten, or protein, in flour, combines to form a web that traps air bubbles and sets. Starch in flour sets as it heats to add to and support the structure. In yeast breads, we want a lot of gluten formation, since it forms a stretchy web that traps carbon dioxide and steam during baking, to give bread its texture (also known as 'crumb'). Fats and sugars help prevent gluten formation. There is some simple sugar available in flour, which feeds the yeast. So if you have a bread recipe with no sugar source, that's okay - the yeast will have enough to 'eat' from the flour. The rising times will just be longer.

Bread flour is high protein flour, and produces bread that has a higher volume because it contains more stretchy gluten. Loaves made with bread flour rest for 10-15 minutes after rising before shaping the loaves so the gluten relaxes a bit and the dough is easier to work. All-purpose flour works just fine for most breads. Whole grain flours do not have as much gluten because there are other ingredients like the bran and germ which get between the gluten molecules. Whole grain flours are usually combined with bread or all-purpose flour to make a better crumb.


Fat
Fat coats gluten molecules so they can't combine as easily, contributing to the finished product's tenderness. Yeast breads that have a high proportion of fat to flour are much more tender, don't rise as high, and have a very tender mouth-feel. Fat also contributes flavor to the bread, and helps the bread brown while baking.


Sugar
Sugar adds sweetness, as well as contributing to the product's browning. The main role for sugar in yeast breads is to provide food for the yeast. As the yeast grows and multiplies, it uses the sugar, forming byproducts of carbon dioxide and alcohol, which give bread its characteristic flavor. Sugar tenderizes bread by preventing the gluten from forming. Sugar also holds moisture in the finished product.


Eggs
Eggs are a leavening agent and the yolks add fat for a tender and light texture. The yolks also act as an emulsifier for a smooth and even texture in the finished product. When lots of eggs are used, they contribute to the flavor of the finished product.


Liquid
Liquid helps carry flavorings throughout the product, forms gluten bonds, and reacts with the starch in the protein for a strong but light structure. Liquids also act as steam during baking, contributing to the tenderness of the product. Yeast needs liquid in order to develop, reproduce, multiply, and form byproducts which make the bread rise.


Salt
Salt strengthens gluten, and adds flavor. Salt enhances flavors. In yeast breads, salt helps moderate the effect of the yeast so the bread doesn't rise too quickly.


Yeast
Yeast is a one-celled plant, available in dried form, instant blend, and live cakes. In yeast bread, yeast multiplies and grows by using available sugars and water, giving off carbon dioxide and ethyl alcohol (fermentation). As long as air is available, the yeast multiplies.

In bread recipes where the bread rises for a second time, you are told to 'punch down' the dough. This breaks up small clusters or colonies of yeast cells so they can get in contact with more air and food, which is why the second rise is usually shorter than the first rise.

When I can find live cakes, I like to use them because I think the flavor is better. However, cake yeast spoils very quickly, so I try to use it within a day of buying it. You can freeze cake yeast. My second choice is active dry yeast, which I feel has a better flavor than instant-rise. Instant-rise yeast has been genetically modified and is packaged with its own food supply, because it rehydrates and becomes active instantly when mixed with liquid. This type of yeast is very convenient, but because the rise is so fast, not much flavor develops from the fermentation process.

Sourdough breads depend on yeast and bacteria starter (mixture of flour, yeast, liquid, bacteria) to provide the special sour flavor. The bacteria lowers the pH of the bread mixture, which adds to the flavor. Since the bread is more acidic (lower pH), this bread keeps longer than ordinary yeast bread. You can make starter in your own kitchen without adding any yeast if you do a lot of yeast bread baking, because the yeast cells are present in your kitchen. If you're new to working with yeast, however, add yeast to your starter.

And here's an interesting point: San Francisco Sourdough bread can only be made in San Fransisco! Scientists discovered that the bacteria in the bread was original to the area, and a wild yeast native to San Francisco was the only type that would grow with the special bacteria. Mixes are now made in that city and shipped to other parts of the country so you can make San Francisco sourdough in your home, but that special bacteria and yeast will not grow in your home kitchen, as they do for ordinary sourdough starters.

http://www.gcsescience.com/rc17-fermentation-yeast-alcohol.htm

Fermentation.

Yeast is a microorganism containing an enzyme which will convert
a sugar (glucose) solution into carbon dioxide and alcohol (ethanol).

The word equation for fermentation is

glucose + yeast carbon dioxide + ethanol.

Carbon dioxide gas bubbles out of the solution into the air
leaving a mixture of ethanol and water.
Ethanol can be separated from the mixture by fractional distillation.
Fermentation must be carried out in the absence of air to make alcohol.
If air is present, ethanoic acid is made instead of alcohol.

Yeast is used in a batch process to make alcohol in beer and wine.
An enzyme in yeast acts on the natural sugar
in malt (to make beer) and grapes (to make wine).
When the alcohol concentration reaches about 10%,
the alcohol damages the yeast and fermentation stops.
In a batch process the reaction vessel must be emptied and cleaned
and then refilled with the new starting materials. A batch process
takes more time and is more expensive than a continuous process.

Different alcoholic drinks contain different amounts of alcohol.
Some people drink alcohol for enjoyment, some drink to excess
and some people become addicted to alcohol.
The harmful effects (physical and social) of drinking excess alcohol
are widespread and reach all parts of society.


Ethanol can be made on a large scale for use as a fuel or solvent
by the hydration of ethene or the fermentation of sugar cane.
Sugar cane is a renewable resource.
Renewable means that the resource can be replaced.
For example more sugar cane can be grown.
Compare this with the use of fossil fuels (the source of ethene)
which are a non-renewable resource.

Yeast is used in the baking of bread.
The carbon dioxide produced causes the bread to rise
and fills the bread full of bubbles.
The alcohol evaporates during the baking process.


Yoghurt and Cheese.

Bacteria can be added to milk to make yoghurt.
An enzyme in the bacteria reacts with sugar in the milk (called lactose)
and converts it into lactic acid.
Lactic acid changes milk proteins and forms the thicker yoghurt.

Cheese is made by adding an enzyme called rennet
after bacteria have produced lactic acid in milk.
Rennet makes milk proteins turn solid and this is the basis for cheese.

BBC Science - DNA

DNA

DNA is the complex chemical that carries genetic information. DNA is contained in chromosomes, which are found in the nucleus of most cells. The gene is the unit of inheritance and different forms of the same gene are called alleles.

Cystic fibrosis is an inherited disorder caused by a faulty allele.

The Human Genome Project has worked out the human DNA sequence, and its data are useful for forensic science and medical research.

What is DNA?

You will remember from your Key Stage 3 studies that the cell's nucleus controls the activities of the cell. Look there if you need to remind yourself of animal and plant cells.

Chromosomes

Chromosomes are X-shaped objects found in the nucleus[nucleus: The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. ] of most cells. They consist of long strands of a substance called deoxyribonucleic acid, or DNA for short. A section of DNA that has the genetic code for making a particular protein is called a gene.

The gene is the unit of inheritance, and each chromosome may have several thousand genes. We inherit particular chromosomes through the egg of our mother and sperm of our father. The genes on those chromosomes carry the code that determines our physical characteristics, which are a combination of those of our two parents.

Nucleus, chromosome and gene

The bases in the DNA molecule carry the different codes needed for different amino acids. The code for a particular amino acid is made from three bases in a particular order. The animation shows the structure of DNA in more detail, but note that you do not need to know this for your examination.

Alleles and genetic disorders

Alleles

Different forms of the same gene [gene: The basic unit of genetic material inherited from our parents. A gene is a section of DNA which controls part of a cell's chemistry - particularly protein production. ] are called alleles - pronounced 'al-eels'. You inherit one allele for each gene from your father and one allele for each gene from your mother. For example, the gene for eye colour has an alleles for blue eye colour and an alleles for brown eye colour. Your eye colour will depend on the combination of alleles you have inherited from your parents.

Genetic disorders

Diseases can be caused by a number of things, including:

• infections eg influenza
• poor diet eg scurvy
• environmental factors eg asbestosis
• spontaneous degeneration of tissues eg multiple sclerosis

Some diseases are inherited from our parents through our genes: they are called genetic disorders. They occur because of faulty alleles. Cystic fibrosis is an example of a genetic disorder.

Cystic fibrosis

People with cystic fibrosis have inherited two faulty alleles, one from their father and one from their mother. They produce unusually thick and sticky mucus [mucus: Slimy white protein, which lines the respiratory tract and alimentary canal. ] in their lungs and airways. Their lungs become congested with mucus, and they are more likely to get respiratory infections. Daily physiotherapy helps to relieve congestion, while antibiotics[antibiotics: Substances that kill bacteria and fungal infections. ] are used to fight infection. The disorder also affects the gut and pancreas, so that food is not digested efficiently.

The Human Genome Project

Base pairs on a DNA molecule

The genetic information in an organism is called its genome. The Human Genome Project, or HGP for short, was started at the end of the last century. It was very ambitious and had several aims, including:

• to work out the order or sequence of all the three billionbase pairs [base pairs: The pairs of nitrogenous bases that connect the complementary strands of DNA. ] in the human genome
• to identify all the genes [genes:The basic units of genetic material inherited from our parents. A gene is a section of DNA which controls part of a cell's chemistry - particularly protein production. ]
• to develop faster methods for sequencing DNA [DNA: The material inside the nucleus of cells, carrying genetic information. DNA stands for Deoxyribonucleic Acid. ]

The sequencing project was finished in 2001, and work continues to identify all the genes in the human genome. The HGP used the DNA of several people to get a sort of average sequence, but each person has a unique sequence (unless they have an identical twin).

Forensic science

Information about a person's DNA can be useful for forensic science. Genetic fingerprinting was invented in 1985 by Sir Alec Jeffreys at the University of Leicester. It uses some of the small differences between the DNA from different people to make a picture rather like a barcode. If enough parts of the DNA are tested, it is very unlikely that two identical DNA fingerprints would belong to two different people. This makes the method very useful for matching samples found at the scene of a crime to people suspected of committing the crime.

Genetic treatment of disease

It is hoped that information from the Human Genome Project will allow scientists to develop new ways of treating or diagnosing illnesses, especially genetic disorders and cancer.

Genetic disorders

A person with cystic fibrosis has inherited two faulty alleles for a certain gene on one of their chromosomes, chromosome 7. It is hoped that it may one day be possible to repair the faulty alleles using gene therapy, perhaps by putting the normal allele into the cells of the lungs. This would greatly improve the lives of people with cystic fibrosis, who often need lung transplants as their illness progresses.

Introduction to Genetics

Genetics is the study of genes, and tries to explain what they are and how they work. Genes are how living organisms inherit features from their ancestors; for example, children usually look like their parents because they have inherited their parents' genes. Genetics tries to identify which features are inherited, and explain how these features are passed from generation to generation.

In genetics, a feature of a living thing is called a "trait". Some traits are part of an organism's physical appearance; such as a person's eye-color, height or weight. Other sorts of traits are not easily seen and include blood types or resistance to diseases. Some traits are inherited through our genes, so tall and thin people tend to have tall and thin children. Other traits come from interactions between our genes and the environment, so a child might inherit the tendency to be tall, but if they are poorly nourished, they will still be short. The way our genes and environment interact to produce a trait can be complicated. For example, the chances of somebody dying of cancer or heart disease seems to depend on both their genes and their lifestyle.

Genes are made from a long molecule called DNA, which is copied and inherited across generations. DNA is made of simple units that line up in a particular order within this large molecule. The order of these units carries genetic information, similar to how the order of letters on a page carry information. The language used by DNA is called the genetic code, which lets organisms read the information in the genes. This information is the instructions for constructing and operating a living organism.

The information within a particular gene is not always exactly the same between one organism and another, so different copies of a gene do not always give exactly the same instructions. Each unique form of a single gene is called an allele. As an example, one allele for the gene for hair color could instruct the body to produce a lot of pigment, producing black hair, while a different allele of the same gene might give garbled instructions that fail to produce any pigment, giving white hair. Mutations are random changes in genes, and can create new alleles. Mutations can also produce new traits, such as when mutations to an allele for black hair produce a new allele for white hair. This appearance of new traits is important in evolution.

Chromosomes

A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.


Chromosomes vary widely between different organisms. The DNA molecule may be circular or linear, and can be composed of 10,000 to 1,000,000,000^[1] nucleotides in a long chain. Typically, eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryoticcells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Also, cells may contain more than one type of chromosome; for example, mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.


Read more on Wikipedia

How to make bread video

Learn How to Make Bread

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Famous Geneticist

James D. Watson (From Wikipedia)

James Dewey Watson (born April 6, 1928) is an American molecular biologist, geneticist, and zoologist, best known as one of the co-discoverers of the structure of DNA with Francis Crick, in 1953. Watson, Francis Crick, and Maurice Wilkins were awarded the 1962 Nobel Prize in Physiology or Medicine "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material".[2] He studied at the University of Chicago and Indiana University and subsequently worked at the University of Cambridge's Cavendish Laboratory in England, where he first met his future collaborator and personal friend Francis Crick.

In 1956, Watson became a junior member of Harvard University's Biological Laboratories, holding this position until 1976, promoting research in molecular biology. Between 1988 and 1992, Watson was associated with the National Institutes of Health, helping to establish the Human Genome Project. Watson has written many science books, including the seminal textbook The Molecular Biology of the Gene (1965) and his bestselling book The Double Helix (1968) about the DNA structure discovery.

From 1968 he served as director of Cold Spring Harbor Laboratory (CSHL) on Long Island, New York, greatly expanding its level of funding and research. At CSHL, he shifted his research emphasis to the study of cancer. In 1994, he became its president for ten years, and then subsequently he served as its chancellor until 2007, when he resigned, due to a controversy over comments he made claiming black Africans were on average less intelligent than whites during an interview.[3]






Francis Crick (From Wikipedia)


Francis Harry Compton Crick OM FRS (8 June 1916 – 28 July 2004) was an English molecular biologist, biophysicist, andneuroscientist, and most noted for being one of two co-discoverers of the structure of the DNA molecule in 1953, together with James D. Watson. He, Watson and Maurice Wilkins were jointly awarded the 1962 Nobel Prize for Physiology or Medicine "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material".[1]


Crick was an important theoretical molecular biologist and played a crucial role in research related to revealing the genetic code. He is widely known for use of the term “central dogma” to summarize an idea that genetic information flow in cells is essentially one-way, from DNA to RNA to protein.[2]


During the remainder of his career, he held the post of J.W. Kieckhefer Distinguished Research Professor at the Salk Institute for Biological Studies in La Jolla, California. His later research centered on theoretical neurobiology and attempts to advance the scientific study of human consciousness. He remained in this post until his death; "he was editing a manuscript on his death bed, a scientist until the bitter end" said Christof Koch.[3]