transcription and translation (bio exam 2)

transcription definition

the synthesis of RNA using DNA as a template

what are the bases in DNA

G, A, T, C

what are the bases in RNA

G, A, U, C

initiation of transcription

1) only one strand of DNA is used as a template for transcription for a particular gene

2) enzyme called RNA opolymerase does the transcriptuon

promoter

segment of DNA with a specific sequence that occurs just “before” the region of DNA is to be transcribed

transcription factors

recognize and bind to the promoter region; recruit RNA polymerase enzyme

Elongation of RNA transcript

• rna polymerase unwinds DNA and adds nucleotides

• only one DNA strand is the template for base-pairing between DNA and RNA nucleotides

• adds RNA nucleotides to the 3’ end; direction of synthesis is 5’>3’

termination of transcription

• RNA polymerase stops adding ribonucleotides and RNA chain is released

• because the new RNA is held to DNA template with hydrogen bonds between bases, if these H-bonds are disrupted the RNA polymerase enzyme terminates transcription since it has no 3’ OH on the growing RNA to add on to

RNA processing steps

1) adds 5’ cap to the end

2) adds poly A tail to the 3’ end

3) RNA splicing- new messenger RNA has exons and introns, the introns are removed and the exons are sliced back together

mRNA

specifies sequence of amino acids in a protein

rRNA

component of ribosome

tRNA

links nucleic acid info in the mRNA to amino acid

genetic code definition

the relationship between nucleotide sequence and amino acid sequence

how RNA triplets are read by ribosomes

• includes specific start codon

  • usually starts with methionine/AUG

• includes 3 stop codons

  • make proteins disassociate

• is non-overlapping and continuous

tRNAS and what they do

• help read mRNA code and insert the right amino acid

• the 3’ end of tRNA is attached to specific amino acid

• the anticodon loop base pairs with codon of mRNA

• the base pair is antiparallel

initiation in eukaryotes

• the initiation complex of 5’ cap of mRNA

• small ribosome and initiation factors scan mRNA for start codon on mRNA

• once that occurs the ribosomal subunit is recruited and binds so translation can begin

elongation in eukaryotes- peptide bond formation

• once the ribosome is assembled, a new tRNA enters the A site

• during elongation amino acids on the tRNA in the Psite transfer to tRNA on the A site

• reaction is catalyzed bu an rRNA molecules in large ribosomal subunit

ribosome movement

the ribosome moves down the codon, which puts the tRNA carrying the polypeptide into the P site and now uncharged tRNA into the E site where it is released. A new tRNA complementary to the next codon binds to the A site

elongation

the polypeptide transfers to the amino acid on the tRNA in the A site. the polypeptide is elongated by repeating steps 3 and 4

termination

when a stop codon is encountered, a release factor enters the A site. the polypeptide is released from the tRNA in the P site, and the ribosome disassociates

codon region definition

region between and including start and stop codon template

template definition

the template for transcription RNA polymerase uses is the DNA chromosome

the template for translation is the mRNA that the ribosome reads to make a protein