Module 1: How DNA codes for proteins

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A-Level- A2 Biology (UNIT 2 MODULE 1- Cellular Control) Mind Map on Module 1: How DNA codes for proteins, created by gillespie_e_ on 03/13/2014.

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Module 1: How DNA codes for proteins
1 GENE: length of DNA (sequence of nucleotide bases that codes for one/more polypeptides- unit of heredity.- about 25,000 in the human genome/ few in mitochondria/ most of them situated on the linear chromosomes within the nucleus> each gene occupies a specific place/locus on the chromosome.
1.1 -Each chromosome consists of one molecule of DNA and each gene is just a part of a DNA molecule. The DNA in the chromosomes is associated with HISTONE PROTEINS.
2 Genes code for polypeptides such as:-structural proteins including collagen and keratin -haemoglobin -immunoglobulins (antibodies) -cell surface receptors -antigens -actin and myosin in muscle cells -tubulin proteins in the cytoskeleton -channel proteins -electron carriers -enzymes
3 THE GENETIC CODE: -triplet code (a sequence of 3 nucleotide bases codes for an amino acid)> there are 4 bases arranged in groups of 3 so the different triplet sequences is 4(cubed) or 64./ there are only 20 amino acids used for protein synthesis. -Degenerate code (all amino acids except methionine have more than one code.-some codes don't correspond to an amino acid but indicate 'stop'> end of the polypeptide
3.1 -Its widespread but not universal- e.g. the base sequence TCT codes for the amino acid serine in any organism.
4 -How does the nucleotide sequence code for the amino acid sequence in a polypeptide?-Genes are on chromosomes in the cell nucleus but proteins are assembled in the cytoplasm, at ribosomes. A copy of the genetic code has to be made which can pass through a pore in the nuclear envelope to the cytoplasm. Messenger RNA (mRNA) is this copy.
5 TRANSCRIPTION: is the creation of a single-stranded mRNA copy of the DNA coding strand.
5.1 TRANSCRIPTION OF A GENE: transcription of a gene. The length of DNA unwinds and unzips. free activated RNA nucleotides pair up and bind temporarily, with hydrogen bonds, to their complementary bases on the template strand of the unwound DNA. Their sugar-phosphate groups are bonded together to form the sugar-phosphate backbone. A single-stranded piece of mRNA, a copy of the coding strand of the DNA. leaves the nucleus through a pore in the nuclear envelope.

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