BIOLOGY 3

1. CELLS
   1. ANIMAL CELLS
      1. NUCLEUS
         1. Contains DNA in the form of chromosomes
      2. CELL MEMBRANE
         1. Holds cell together & controls what goes in/out
      3. RIBOSOMES
         1. Where protein synthesis occurs
      4. CYTOPLASM
         1. Gel-like substance where most of the cell's chemical reactions happen
      5. MOTICHONDRIA
         1. Where most of the reactions involved in respiration take place
            1. Liver cells - carry out lots of energy- demanding metabolic reactions
            2. Muscle cells - which need energy to contract and cause movement
   2. PLANT CELLS
      1. Nucleus, cell membrane, cytoplasm
      2. CELL WALL
         1. Made of cellulose - supports the cell
      3. CHLOROPLASTS
         1. Where photosynthesis occurs
      4. VACUOLE
         1. Contains cell sap: weak solution of sugar&salts
   3. BACTERIAL CELLS
      1. Cytoplasm
         1. Cell membrane
            1. Cell wall
               1. NO chloroplasts or mitochondria
                  1. NO TRUE NUCLEUS: circular strand of DNA
2. DNA
   1. CHROMOSOMES
      1. Long molecules of coiled up DNA.
         1. DNA is divided up into small sections called genes
            1. DNA is a double helix. Each of the two DNA strands is made up of lots of small groups called 'nucleotides'
               1. Each nucleotide contains a base
                  1. Complimentary base pairings: A & T and C & G
                     1. In order to copy itself, the double helix unzips
   2. WATSON & CRICK
      1. First scientists to build a model of DNA - 1953
         1. They used data from other scientists to help them understand the structure, EG:
            1. X-ray data showing that DNA is a double helix formed from 2 chains wound together
               1. Other data showing that bases occurred in pairs
                  1. New discoveries like this weren't widely accepted straight away. Other scientists needed to repeat the work first to make sure the results were reliable
3. PROTEIN SYNTHESIS
   1. DNA molecules contain a genetic code that determines which proteins are built. The proteins determine how all the cells in the body function
   2. Proteins are made up of chains of molecules called amino acids. Each different protein has its own particular number and order of amino acids
      1. This gives each protein a different shape, which means each protein can have a different function
         1. THE ORDER OF BASES IN A GENE DECIDES THE ORDER OF AMINO ACIDS IN A PROTEIN
            1. EACH AMINO ACID IS CODED FOR BY A SEQUENCE OF THREE BASES IN A GENE
               1. The amino acids are joined together to make proteins, following the order of bases in the gene.
                  1. Each gene contains a different sequence of bases
   3. GENE = a section of DNA that codes for a particular protein
   4. mRNA carries the code to the ribosomes
      1. Proteins are made in the cell cytoplasm by ribosomes, which use the code in the DNA
         1. mRNA is made by copying the code from the DNA
            1. The mRNA carries the coe between the DNA and the ribosome
         2. Ribosomes are too small to be seen under a microscope

1. PROTEIN PRODUCTION
   1. Different cell types have different functions because they have different proteins
      1. Only some of the full set of genes is is used in any one cell
         1. Some are switched off - the proteins they code for aren't produced
            1. The genes that are switched on determine the function of a cell
   2. PROTEIN FUNCTIONS
      1. Carrier molecules
         1. used to transport smaller molecules - EG: haemoglobin in RBCs binds to oxygen molecules and transports them
      2. Hormones
         1. used to carry messages around the body - EG insulin is a hormone released into the blood by the pancreas to regulate blood sugar level
      3. Structural proteins
         1. physically strong - EG collagen strengthens connective tissues like ligaments and cartilage
2. ENZYMES
   1. Biological catalysts: control cell reactions
      1. Reduce the need for high temperatures & we only have enzymes to speed up the useful chemical reactions in the body
         1. Each biological reaction has its own specific enzyme & each enzyme is coded for by a different gene
   2. LOCK AND KEY
      1. Chemical reactions usually involve things either being split apart or joined together
         1. The substrate is the molecule changed in the reaction
      2. Each enzyme has an ACTIVE SITE - the part where it joins on to its substrate to catalyse the reaction
         1. Enzymes usually only work with one substrate: they have a HIGH SPECIFICITY FOR THEIR SUBSTRATE
            1. For an enzyme to work it has to fit the active site: no fit = no catalyst
               1. The substrate fits the enzyme like a lock fits a key
   3. OPTIMUM TEMPERATURE
      1. Usually, higher temp = faster rate and vice versa: more heat = more energy = more (successful) collisions
         1. Too hot: some of the bonds break & the enzyme denatures
            1. It loses its shape so its active site doesn't fit the substrate - the enzyme can't function
               1. Optimum temp = reaction goes fastest/just before denaturing
   4. OPTIMUM pH
      1. If pH is too high or low, it interferes with the bonds holding the enzyme together & it denatures
         1. Usually neutral but not always
            1. Pepsin: breaks down proteins in the stomach: works best at pH 2
   5. Q10
      1. Shows how much the rate changes when the temp is raised by 10
         1. Q10 = rate at higher temp / rate at lower temp
3. MUTATIONS
   1. A change in the DNA base sequence
      1. If a mutation occurs in a gene, it could stop the production of the gene it normally codes for/produce a different protein
   2. Most mutations are harmful, some are beneficial, some have no effect:
      1. In reproductive cells, offspring might develop abnormally
         1. In body cells, mutant cells can multiply uncontrollably & invade other parts of the body: cancer
      2. Sometimes a new protein produced is an improvement on the one it was supposed to be, giving the organism a survival advantage
   3. Radiation and certain chemicals cause mutations
      1. Ionising radiation eg x-rays and UV light: the greater the dose of radiation, the greater the chance of mutation
      2. Mutagens: if the mutations produce cancer: carcinogens.
         1. Cigarette smoke contains chemical mutagens

Annotations:

• Respiratory quotient:  RQ = CO2 produced / O2 used 0.7 < RQ < 1 = aerobic RQ > 1 = anaerobic 

1. THE REACTION OF GLUCOSE WITH OXYGEN TO RELEASE ENERGY
   1. Energy made in respiration can't be used directly by cells - so it's used to make ATP
      1. ATP = energy source for cell processes and transports energy
         1. Respiration is controlled by enzymes: affected by temp & pH
            1. Needed for: muscle contraction, protein synthesis, control of body temp
2. AEROBIC
   1. glucose + oxygen --> carbon dioxide + water
      1. C6H1206 + 6O2 --> 6CO2 + 6H20
         1. When respiration rate increases, oxygen consumption and carbon dioxide production increase
            1. The rate of oxygen consumption can be used to estimate metabolic rate
3. ANAEROBIC
   1. glucose --> lactic acid
      1. C6H12O6 --> C3H6O3
      2. without oxygen: much less energy per glucose molecule
         1. Glucose only partially broken down
            1. Lactic acid builds up in muscles: pain & muscle fatigue
      3. OXYGEN DEBT
         1. Extra oxygen needed to break down the built up lactic acid & begin aerobic respiration again
            1. You keep breathing hard when you stop to repay the debt
               1. Lactic acid is carried to the liver to be broken down so your heart rate stays high too

1. BEING MULTICELLULAR
   1. ADVANTAGES
      1. allows organism to be larger
      2. allows for cell differentiation
      3. allows organism to be more complex
   2. REQUIRES SPECIALISED ORGAN SYSTEMS
      1. communication between cells
      2. supplying cells with nutrients
      3. controlling exchanges with the environment
2. MITOSIS
   1. 1 diploid cell
      1. DNA replicates before division
         1. Chromosomes line up at centre of cell
            1. Chromosomes divide to opposite poles of the cell
               1. 2 genetically identical diploid cells
3. MEOSIS
   1. 1 diploid cell
      1. DNA replicates before division
         1. 1 chromosome from each pair separates to opposite poles of the cell in the 1st division
            1. Crossing over adds to genetic variation
               1. Chromosomes separate to opposite poles of the cell in the 2nd division
                  1. Makes 4 genetically different haploid cells - gametes