Studied by 1 persontranscription
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
Note
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