d1.2 protein synthesis

transcription

process of making RNA from a DNA template

what does RNA polymerase do in Transcription?

• binds to promoter region

• unwinds DNA,

• adds complementary nucleotides

• makes RNA from template DNA strand

what is the result of transcription 

mRNA 

what does mRNA from transcription do?

carries genetic code from DNA to ribosome for protein synthesis 

what is the promoter region?

• part in DNA where RNA polymerase is attracted to start 

what happens on the inside of RNA polymerase in DNA transcription?

• DNA is unwound 

• codons/complementary nitrogenous bases are matched to the template strand

• after RNA passes through, the DNA strands join again via hydrogen bonding and leaves RNA polymerase

• continues until terminator region

what is different about RNA polymerase base pairing

Adenine pairs with Uracil

what strand is copied to make RNA

Template/anti sense strand

what strand has the same base sequence as the mRNA created but Thymine is replaced with Uracil?

Coding/Sense strands 

why is DNA template stability essential? DNA template must be uncharged

• accurate transcription 

• proper cell function 

what is gene expression

process in which information from a gene/DNA is used to make a function product ex a protein 

how do cells regulate/control gene expression 

By turning transcription on or off

why do cells control transcription?

• controls which proteins are produced according to the cell’s needs 

• allows cells to respond to changes 

• saves energy 

what are the steps of gene expression

Transcription and Translation

what is translation?

process of building a polypeptide/protein based off of mRNA

what determines the amino acids in the polypeptide?

sequence of bases in mRNA

how does translation work?

• anticodons are brought by tRNA based on the codons in RNA 

• tRNA carries the corresponding amino acids 

• process repeats

where does translation occur?

cytoplasm

where are the anticodons on?

tRNA has an anticodon that pairs with the mRNA codon

how does mRNA, tRNA and ribosomes work together work together in translation?

• mRNA binds to small subunit of the ribosome

• ribosome reads the mRNA codons

• two tRNA attach to the large subunit 

what do the two tRNA molecules do at the large subunit of the ribosome?

• one holds the growing polypeptide chain 

• the other brings the next amino acids

what does the ribosome do in translation?

• provides a site where translation happens

• has two subunits, the small and large

what does the small subunit of the ribosome do in translation

binds mRNa

what does the large subunit of the ribosome do in translation

• gives a site for tRNA binding and peptide bond formation

what does degeneracy mean?

more than one codon can code for the same amino acid, provides a safeguard against some mutations 

Universality

• genetic code is the same in all living organisms

• same codon codes for same amino acid 

how does tRNA move with the mRNA

• start codon binds to anticodon brought by tRNA

• the next tRNA brings the next anticodons that codes for the next codon in mRNA

• amino acid brought by new anticodon takes old amino acid and polypeptide chain

• the now empty tRNA leaves ribosome 

what is mutation?

mutation is a change in the DNA base sequence

• can alter the sequence of amino acids in a protein, changing its structure and function 

what is a point mutation

changes to a single base in the DNA sequence

what can a point mutation lead to?

missense, nonsense and silent mutation

on a base level how is sickle cell anemia started?

• happens in the gene for hemoglobin 

• DNA is altered, adenine is replaced by thymine 

• this affects the protein in hemoglobin, altering its shape and making red blood cells into a sickle shape 

what is the directionality of both transcription and translation

5’ to 3’

during transcription, where does RNA polymerase add RNA nucleotides to?

the 3’ end of the growing RNA strand

in what direction is the template DNA strand read in during Transcription?

3’ to 5’

how does transcription start?

• special proteins called transcription factors bind to promoter region 

• help RNA polymerase attach to the DNA at the promoter 

what does the promoter control?

where and when a gene is transcribed

how do transcription factors regulate gene expression 

they control RNA polymerase binding 

what are non coding sequences

sections of DNA that do not code for proteins

what do regulators of gene expression do

control when and how much genes are turned on or off ex promoters

what are introns?

• non coding sections

• removed during RNA processing

what are telomeres

• non coding sections

• protective caps at the end of chromosomes

• prevent damage or fusion 

what is post transcription modification

when the initial RNA transcript is chemically altered to make mature mRNA

what are the steps of post transcriptional modification

• capping 

• polyadenylation 

• splicing 

what is initiation of translation

• first step in making proteins 

• ribosome assembles on the mRNA 

• happens in cytoplasm 

what are the initial steps of initiation of translation?

• small ribosome attaches to 5’ end of mRNA

• scans mRNA to find start codon

• initiator tRNA carrying the amino acid for the start codon binds at P site

• second tRNA carrying amino acid binds to A site

what does the A site of the ribosome do in translation?

Holds tRNA with the next amino acid to be added

what does the P site of the ribosome do in translation?

holds tRNa carrying the polypeptide chain, starts with initiator tRNA

what does the E site of the ribosome do in translation?

where empty tRNA leaves the ribosome after its amino acid is added

what does tRNA synthase do?

catalyzes peptide bond formation during translation

what are telomeres?

protective ends of chromosomes

what happens post transcription before translation?

• capping on 5’ end

• 3’ poly adenine tail is added to stabilize RNA

• splicing- introns are removed by spliceosome and exons are joined