Biology B3

Biology B3

DNA structureDNA 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.Chromosomes are X-shaped objects found in the nucleus 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- the central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. 

Most cells in your body have a nucleus which contains your genetic material in the form of chromosomes. In most animal cells chromosomes come in pairs- but different species have a different number of pairs. For example, a human has 23 pairs of chromosomes and a guinea pig cell nucleus contains 32 pairs. Chromosomes carry genes. Different genes control the development of different characteristics, e.g. eye colour.  A gene is a short length of the chromosome which is quite a long length of DNA. The DNA is coiled up to form the arms of the chromosome. 

There can be different versions of the same gene, which give different versions of a characteristic, like blue or brown eyes. The different versions of the same gene are alleles instead of genes. 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.

Chromosomes Chromosomes are long molecules of coiled up DNA which is divided up into short sections called genes.DNA is a double helix (a double stranded spiral). Each of the two DNA strands is made up of lots of small groups called "nucleotides". Each nucleotide contains a small molecule called a "base". DNA has four different bases.You only need to know the four bases by their first initials A, C, G and T. This is called complementary base-pairing.

WATSON AND CRICKFrancis Crick and James Watson were the first scientists to build a model of DNA in 1953. They used data from other scientists to help them understand the structure of the molecule. *Don't forget that new discoveries like Watson and Crick's were not widely accepted straight away. Other scientists need to repeat the work first to make sure the results are reliable.

Genetic disordersDiseases 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 calledgenetic disorders. They occur because of faulty alleles. Cystic fibrosis is an example of a genetic disorder.

Cystic fibrosisPeople with cystic fibrosis have inherited two faulty alleles, one from their father and one from their mother. They produce unusually thick and sticky mucus 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, whileantibiotics are used to fight infection. The disorder also affects the gut and pancreas, so that food is not digested efficiently.

Mucus- Slimy, whit protein, which lines the respiratory tract and alimentary canal. Antibodies- substances that kill bacteria.

MutationsA mutation is a change in the DNA base sequence that could stop thee production of the protein the gene normally codes for- or it might mean a different protein is produced instead.Producing the wrong or no protein can be a disaster if the protein was an important enzyme. If a mutation occurs in reproductive cells, then the offspring might develop abnormally or die. If a mutation occurs in the body cells, the mutant cells can multiply uncontrollably and invade parts of the body, this is cancer. Sometimes Mutations are beneficial or have no effect. The mutation can be passed on to offspring until it becomes common in the population. This is natural selection and evolution. 

EnzymesEnzymes are biological catalysts - catalysts are substances that increase the rate of chemical reactions without being used up. Enzymes are also proteins that are folded into complex shapes that allow smaller molecules to fit into them. The place where these substrate molecules fit is called the active site.Chemical reactions usually involve things either being split apart or joined together. The substrate is the molecule changed in the reaction. Every enzyme has an active site- the part where it joins on to its substrate to catalyse the reaction. Enzymes are really picky- they usually only work with one substrate. The posh way of saying this is that enzymes have a high specificity for their substrate. This is because, for the enzyme to work, the substrate has to fit into the active site. If the substrate's shape doesn't match the active site's shape, then the reaction won't be catalysed. this is called the 'lock and key' mechanism, because the substrate fits into the enzyme. 

Temperature and EnzymesAs the temperature increases, so does the rate of reaction. But very high temperatures denature enzymes.The graph shows the typical change in an enzyme's activity with increasing temperature. The enzyme activity gradually increases with temperature until around 37ºC, or body temperature. Then, as the temperature continues to rise, the rate of reaction falls rapidly, as heat energy denatures the enzyme.

pH and EnzymesChanges in pH alter an enzyme’s shape. Different enzymes work best at different pH values. The optimum pH for an enzyme depends on where it normally works. For example, intestinal enzymes have an optimum pH of about 7.5. Enzymes in the stomach have an optimum pH of about 2.

The Q10 value for a reaction shows how much the rate changes when the temperture is raised by 10 *C. You can calculate it by using this equation:Q10 = rate at higher temperature / rate at lower temperature

Respiration is not the same thing as breathing. That is more properly called ventilation. Instead, respiration is a chemical process in which energy is released from food substances, such as glucose - a sugar.Aerobic respiration needs oxygen to work. Most of the chemical reactions involved in the process happen in tiny objects inside the cell cytoplasm, called mitochondria.This is the equation for aerobic respiration:glucose + oxygen    →    carbon dioxide + water (+ energy)The energy released by respiration is used to make large molecules from smaller ones. In plants, for example, sugars, nitrates and other nutrients are converted into amino acids. Amino acids can then join together to make proteins. The energy is also used: to allow muscles to contract in animals to maintain a constant body temperature in birds and mammals

Respiratory Quotant (RQ)RQ is calculate using the following formula:RQ = carbon dioxide / oxygen used For aerobic respiration using glucose, RQ = 1.

ProteinsProteins are polymers. They are built up in cells when monomers called amino acids join together end to end:Lots of amino acid molecules → a protein molecule

Polymer-  a polymer is a large molecule formed from many identical  smaller molecules (Monomers).Monomer- an atom or small molecule that bonds with other monomers to form a polymer e.g. amino acid monomers forming a protein polymer. 

There are only about 20 different naturally occurring amino acids. However, each protein molecule has hundreds, or even thousands, of them joined together in a unique sequence. This gives each protein its own individual properties. Different proteins The long chains of amino acids fold to give each type of protein molecule a specific shape. Proteins act as: Structural components of tissues (such as muscles) Hormones (such as insulin) Antibodies (part of the body's immune system) Biological catalysts (enzymes) The particular shape that a protein molecule has allows other molecules to fit into it. This is particularly important for antibodies and enzymes.

New Page