Biology Notes: DNA Structure, Mitosis and Meiosis PDF

CBA 2 Y3 content: 1.​ List the chemical elements which make up: -​ Carbohydrates: Carbon Hydrogen Oxygen -​ Fats: CHO -​ Proteins: CHO Nitrogen (Sulphur) 2.​ State primary structure, secondary structure, tertiary structure & quaternary structure of proteins 3.​ State the mai...

CBA 2 Y3 content: 1.​ List the chemical elements which make up: -​ Carbohydrates: Carbon Hydrogen Oxygen -​ Fats: CHO -​ Proteins: CHO Nitrogen (Sulphur) 2.​ State primary structure, secondary structure, tertiary structure & quaternary structure of proteins 3.​ State the main roles of carbohydrates, fats and proteins in living organisms -​ Carbohydrates: immediate source of energy -​ Fats: insulation to prevent excessive heat loss & long-term storage of energy -​ Proteins: required for synthesis of new protoplasm for growth & repair of worn out cells 4.​ Describe tests for -​ Starch: using iodine in potassium iodide solution -​ +ve: mixture turned from yellowish-orange to blue black -​ -ve: mixture remained yellowish-orange -​ Reducing sugars: using benedict’s solution -​ +ve: brick red ppt (large amount) / orange (moderate) / yellow (low) / green (trace) obtained from blue mixture -​ -ve: mixture remained blue -​ Protein: using biuret solution -​ +ve: mixture turned from blue to violet/lilac -​ -ve: mixture remained blue -​ Fats: using ethanol -​ +ve: white emulsion formed when water was added -​ -ve: mixture remained clear when water was added 5.​ State that large molecules are synthesised from small basic units: -​ Cellulose, glycogen & starch from glucose -​ Polypeptides & proteins from amino acids -​ Lipids such as fats from glycerol & fatty acids DNA structure & function 1.​ Outline the relationships among DNA, genes and chromosomes -​ Genes are chunks of DNA, chromosomes are long strands of DNA which contain many genes 2.​ State that DNA is a double helix comprising two strands of nucleotides, each nucleotide formed of a sugar, a phosphate group and one of four different bases (AGCT) 3.​ Understand the role of condensation reactions in joining the components of nucleotides and in the formation of di- and polynucleotides (phosphodiester bond) 4.​ State the rule of complementary base pairing -​ Guanine to cytosine & adenine to thymine 5.​ Outline the process of semi-conservative DNA replication -​ Begins at the origin of replication (ori) -​ Helicase unwinds the double helix by breaking the H bonds between the complementary base pairs in the parental strands -​ Each parental strand acts as a template for the synthesis of a new DNA strand -​ Primase attaches to the unwound chain and catalyses the synthesis of RNA primer to provide free 3’ OH ends for DNA polymerase III -​ DNA polymerase III elongates the new daughter strand in the 5’ to 3’ direction by catalysing phosphodiester bond formation between the incoming deoxyribonucleotides and the free 3’ OH end of the daughter strand -​ Free deoxyribonucleotides are incorporated by complementary base pairing to the parental DNA strands, with adenine to thymine and guanine to cytosine -​ In a replication fork, the leading strand is synthesized continuously while the lagging strand is synthesised discontinuously to form Okazaki fragments -​ RNA primers are removed and replaced by deoxyribonucleotides by DNA polymerase I -​ Nicks between the okazaki fragments are filled in by DNA ligase by forming phosphodiester bonds between the Okazaki fragments 6.​ Explain how gel electrophoresis is used to analyse DNA, including how the DNA fragments on a gel are visible and the role of DNA markers in identifying DNA fragments of different size -​ Principle of how this works: -​ DNA has a negative charge & will migrate towards the anode under an electric current. The agarose gel acts as a molecular sieve to separate DNA based on size. DNA fragments, which have longer/heavier molecular weight will migrate slower and hence travel a shorter distance than those which are shorter/lighter molecular weight. -​ Loading dye (DNA markers) -​ Contains dyes to track how ‘fast’ DNA is migrating across the agarose gel -​ One dye is smaller than most or all DNA fragments, therefore will run as fast/faster than the smallest DNA fragments -​ The other dye is large, and will migrate along with the very large DNA fragments -​ DNA sample is somewhere in between the dyes, so when the small due gets near the end of the gel, the gel is stopped -​ Glycerol to render DNA samples denser than the running buffer so that DNA samples will sink into the well -​ How fragments are visible: -​ A dye has to be used to stain the agarose gel before or after electrophoresis -​ The nucleic acid dyes bind to DNA to form a complex, which can then be visualised by exposing the gel to UV or blue light  Gel Electrophoresis Cell cycle, Mitosis & Meiosis 1.​ State that mitosis (asexual reproduction) is a type of cell division giving rise to genetically identical cells in which the chromosome number is maintained 2.​ State the importance of mitosis in growth, repair and asexual reproduction 3.​ Describe with the aid of diagrams, the behavior of chromosomes during mitosis & the associated behaviour of the nuclear envelope, cell membrane and centrioles 4.​ Distinguish between nuclear division and cytokinesis with reference to both plant & animal cells -​ Nuclear division is division of nucleus, cytokinesis is division of cytoplasm during last stage of cell division 5.​ Identify causative factors of cancerous growth (carcinogens -> highly likely to cause damage to DNA molecules resulting in mutation) -​ Ionising radiation (including x-rays and gamma rays) may trigger formation of damaging ions in the nucleus leading to the break-up of the DNA -​ Non-ionising radiation (UV light) less penetrating than ionising radiation but if absorbed by the nitrogenous base of DNA, may modify it, disrupting complementary base pairing -​ Chemicals such as tar, prolonged exposure to asbestos 6.​ Describe the development of cancer as a multi-step process that includes accumulation of mutations, angiogenesis and metastasis -​ Accumulation of mutation: results in uncontrolled cell division (rate of cell multiplication is much faster than rate of cell death) & a tumour is formed -​ Angiogenesis: more mutations may result in a malignant tumour developing which promotes growth of new blood vessels to provide oxygen and nutrients -​ Metastasis: tumour may spread to and establish in other locations of the body 7.​ Define the terms haploid & diploid, and explain the need for a reduction division process prior to fertilisation in sexual reproduction (meiosis) -​ Haploid cell has one set of chromosomes -​ Diploid cell has 2 sets of chromosomes, one set from the female parent and other from male parent -​ Need for reduction division process: reduces number of chromosomes to half so that when egg & sperm fuse, baby will have correct number of chromosomes 8.​ State what is meant by a homologous pair of chromosomes -​ Matching pairs of chromosomes that can possess different versions of the same genes/alleles -​ One member of the pair comes from the female parent and the other comes from the male -​ They have the same size, shape & sequence of genes 9.​ State that meiosis is a type of cell division that gives rise to genetically dissimilar cells in which the chromosome number is halved due to the separation of homologous chromosomes 10.​State that meiosis is used in the formation of gamete 11.​State and explain how meiosis and fertilisation can lead to genetic variation -​ Independent assortment of maternal & paternal homologous chromosomes -​ The way the chromosomes of each homologous pair line up at the equator of the spindle in meiosis I is entirely random -​ Which chromosome of a given pair goes to which pole is independent of the behaviour of the chromosomes in other pairs -​ Crossing over of segments of individual maternal & paternal homologous chromosomes -​ Results in new combination of alleles on the chromosomes of the haploid cells produced -​ Generates an almost unimaginable degree of variation -​ Random fusion of male & female gametes in sexual reproduction