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Module 1: How
DNA codes for
proteins
- 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.
- -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.
- -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.
- 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
- 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
- -Its widespread but not universal- e.g.
the base sequence TCT codes for the
amino acid serine in any organism.
- -Its widespread but not universal- e.g.
the base sequence TCT codes for the
amino acid serine in any organism.
- -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.
- TRANSCRIPTION: is the creation
of a single-stranded mRNA copy of
the DNA coding strand.
- 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.
- 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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