Biology - genes, chromsomes and protein synthesis

prokaryotic vs eukaryotic DNA

Prokaryotic - free in cytoplasm, circular DNA/plasmids, short, single cicrular chromosome, not associated with histones

Eukaryotic - in nucleus, long, linear double helix, associated with histones

DNA in mitocondria and chloroplasts

small, circular, not associated with histones

endosymbiotic theory

suggests bacterial origins of these eukaryotic organelles - evolved from free living aerobic bacteria which were engulfed by an ancestral eukaryotic cell

genetic code - degenerate

more than one codon codes for one amino acid

genetic code - non-overlapping

each base in the sequence is only read once

bases in mRNA

A C G U

Gene

sequence of bases on a DNA molecule that code for a protein (polypeptide which results in a characteristic)

Locus

the fixed position of a gene on a chromosome (alleles of genes are found at the same locus on each chromsome pair)

homologous pair

two chromosomes in a diploid cell that carry the same genes in the same order with one inherited from each parent

why wouldn’t a ‘doublet’ code work

only code for 16 amino acids

three stop codons

UAA UAG UGA

start codon that codes for amino acid methionine

AUG

introns

non - coding sections of DNA thought to be remnants of sequences earlier in evolution and needed for gene regulation

exon

coding sequences of DNA within a gene that are expressed

genome

complete set of genetic material for an organism

proteome

full range of proteins that an organism is able to express/produce at a given time

mRNA

• single stranded

• AGCU

• codons

• for transcription, translation, processing transport, genetic code

tRNA

• single stranded with internal hydrogen bonds to hold the cover leaf structure (and ester bonds)

• anticodons

• amino acid transport, codon recognition, peptide bond formation, ribosome binding

transcription

• makes pre mRNA

• DNA helicase causes two strands to separate, exposing nucleotide bases

• free RNA nucleotide bases from nucleus pair up with complemetary bases on one tempate strand

• RNA polymerase moves along the strnad joining bases together with phosphodiester bonds to form mRNA

• stops when RNA polymerase reaches a stop codon and detaches

• in eukaryotes - splicing removes introns joining exons to get functional mature mRNA for translation, spliceosome identifies, loopx, cuts, joins, releases intron for recycling, prokaryotes generally lack introns

translation

• codons on mRNA match to anticodons on tRNA to form a polypeptide chain with amino acids

• mRNA leaves nucleus via nuclear pore to ribosome and collects specific amino acids complementary to its binding site

• ribosome attaches to 5’ end of mRNA molecule

• anticodon of t is complementary to codon of m and bind - two tRNA molecules attach at once join by a peptide bond - condensation reaction linking carboxyl group of chain to amino group of new amino acid peptidyl transferase

• tRNA detaches and collects another amino acid, ribosome moves along mRNA until stop codon is reached and polypeptide chain detaches

transcription vs DNA replication

• both use DNA templates, enzymes and unwind double helix

• t uses RNA polymerase, DNA rep. uses DNA polymerase

• t produces single stranded RNA moleucule, DNA rep. produces two double stranded DNA molecules

• t copies small segments, DNA rep. copies a complete set of DNA - genome

• t uses one template strand, DNA rep. uses two

organelle used to modify protein

er, golgi apparatus

up to - ribosomes can pass behind first so many polypeptides can be assembled simultaneously = polysome system

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