hl ib biology- protein synthesis

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transcription

transcription

the process of copying a segment of DNA into RNA.

rna polymerase

binds to the site of dna at the start of the gene being transcribed

unwinds the dna double helix

moves along the template strand putting rna nucleotides on the template strand

links the rna nucleotides by covalent sugar- phosephate bonds

detaches the rna frim the template strand allowing the dna helix to reform

transcription stops when a sequence reaches a stop codon

role of hydrogen bonding in transcription

each nucleotide added to the growing rna strand by rna polymerase must have a base that is complementary or else it cant form a hydrogen bond

sense/coding strand

the dna strand with the base sequences that are being copied into rna

antisense strand

the dna strand that isnt being copied into rna

gene expression

the process by which information carried by agene has obsrvable effects on an organism

the proteins produced directly detirmine the observable characteristics of an organism

only some genes r switched on in a cell

making a specific polypeptide

amino acids must be linked together in the correct sequence

the info needed to make a polypeptide is held in the base sequence of an rna molecule

mRNA

messanger rna, its the rna with the info that codes for a polypeptide

role of mRNA

mRNA has a site to which a riboseome can bind and a sequence of codons that specifies the amino acid sequence of the polypeptide

one mRNA molecule can be translated many times

tRNA (transfer RNA)

translates the base sequence of mRNA into the amino acid sequence of a polypeptide

to do this, theres an attachment point for the amino acid that corresponds to the anti-codon

ribosome function in translation

site of protein synthesis

subunits of ribosomes function

the smaller unit has a binding site for mRNA and the large subunit has 3 binding sites for tRNA

the large subunit also has a catalytic site that makes peptide bonds between the amino acids to assemble the polypeptide

complementary base pairing between tRNA and mRNA

the 3 bases of an anti-codon on a tRNA must be complementary to the 3 bases on the codon on the mRNA for the tRNA to bind to the ribosomes

features of genetic code

the data in dna bases are the amino acid sequences of a polypeptide

there are 64 combinations of 3 bases

degeneracy and universality

codon

a sequence of 3 bases

forms a unit of genomic information

movement of ribosomes along mRNA

translation of mRNA molecules is done by a repeating cycle of steps

each cycle results in the addition of one amino acid to the growing peptide chain

movement of ribosomes along mRNA translation steps

1) an ezyme with an active site that fits the tRNA binds to it and attaches the specific amino acid

2) the tRNA carrying a single attached amino acid binds to the A-site on the ribosome, with its anticodon linked by complementary base paring

3) the single amino acid on the tRNA is linked to the end of the growing polypeptide by a peptide bond

4) the tRNA moves from the A-site to the P-site as the ribosome moves along the mRNA one codon at a time

5) the polypeptide held by the tRNA is transferred to another tRNA thats arrived at the A-site

6) the tRNA moves from the P-site to the E-site. (exit site) as the ribosome moves along, the anti-codon od the tRNA seperates from the codon on the mRNA

gene mutaton examples

sickle cell disease

gene mutation

the change to the base sequence of a gene

can happen with even a single base change

directionality of transcription and translation

both r 5’ to 3’

promoter

a section of dna that indicates gene translation

allows dna polymerase to bind alonf

examples of base sequence functions

1) bases can be transcribed to produce rRNA

2) regulation of gene expression

3) telometers (ends of chromosomes)

intons

base sequences that are edited out of mRNA/ arent expressed

post transcriptional modification

in prokaryotes, rna can be translated as soon as its been transcribed

newly produces rna must be mature before transcription

exons

coding sequences that are expressed by translation

splicing of exons

splicing exons is important bc it allpws polypeptides to form and function w/ out having to duplicate a gene

steps to initiate translation

an activating enzyme attaches methionine to an initiator tRNA

the indicator tRNA binds to the small subunit of the ribosome, which creates a terrary complext

the terrary complex binds to the 5’ of the mRNA and slides along it

the small subunit stops moving along the mRNA

types of polypeptide modification

changes to side chains

folding

combining 2 or more polypeptides

recycling of amino acids

proteins have a short life span

cell activities might change

protein is denatured