AP Bio - transcription

amino acids are linked by

peptide bonds

the process by which DNA directs the synthesis of proteins

gene expression

two stages of gene expression

transcription and translation

the synthesis of RNA using information from DNA

transcription

transcription allows for:

the “message” of DNA to be transcribed

transcription occurs

in the nucleus

the synthesis of a polypeptide using information from RNA

• occurs at the ribosome

• a nucleotide sequence becomes an amino acid sequence

translation

this type of RNA:

• is synthesized during transcription using a DNA template

• carries information from the DNA to the ribosomes in the cytoplasm

mRNA

this type of RNA:

• important in the process of translation

• each can carry a specific amino acid

• can attach to mRNA via their anticodon

  • a complimentary codon to mRNA

  • allow information to be translated into a peptide sequence

tRNA

this type of RNA:

• helps form ribosomes

• helps link amino acids together

rRNA

groups of 3 nucleotides are called

triplets/ codons

mRNA molecules formed ____________ and ______________ to the DNA nucleotides

antiparallel, complimentary

more than one codon for each amino acid is called

redundancy

the codons on the mRNA must be read in the correct groupings during translation to synthesize the correct proteins

reading frame

taking DNA and making an RNA messenger

transcription

three steps of transcription

initiation, elongation, and termination

transcription begins when:

RNA polymerase molecules attach to a promoter region of DNA

• do not need a primer to attach

• promoter regions are upstream of the desired gene to transcribe

• promoter region is called the TATA box

• transcription factors help RNA polymerase bind

initiation in eukaryotes

RNA polymerase can bind directly to the promoter

initiation in prokaryotes

promoter is always ___________ of the gene of interest to be transcribed

upstream

____ _______________ opens the DNA and reads the triplet code of the template strand

• moves in the 3’ to 5’ direction

• mRNA transcript elongates 5’ to 3’

RNA polymerase

RNA polymerase moves in which direction

downstream

1. pairing of complimentary RNA nucleotides

2. the growing mRNA strand peels away from the DNA template strand

3. DNA double helix then reforms

process of elongation

a single _____ can be transcribed simultaneously by several _____ _______________ molecules

• helps increase mRNA production

gene, RNA polymerase molecules

proceeds through a termination sequence

• causes a termination signal → RNA polymerase detaches

  • mRNA transcript is released and proceeds to translation

    • mRNA does NOT need modifications

termination in prokaryotes

RNA polymerase transcribes a sequence of DNA called the polyadenylation sequence

• codes for a polyadenylation signal

  • releases pre-mRNA from the DNA

    • must undergo modifications before translation

termination in eukaryotes

three modifications to pre-mRNA before translation

1. 5’ cap

2. poly-A tail

3. RNA splicing

the 5’ end of the pre-mRNA receives a modified guanine nucleotide “cap”

5’ cap

the 3’ end of the pre-mRNA receives 50-250 adenine nucleotides

poly-A tail

• help the mature mRNA leave the nucleus

• help protect the mRNA from degradation

• help ribosomes attach to the 5’ end of the mRNA when it reaches the cytoplasm

function of the 5’ cap and poly-A tail

sections of pre-mRNA, called introns, are removed and the exons are joined together

RNA splicing

intervening sequences, code for amino acids

introns

expressed sections, code for amino acids

exons

why does splicing occur?

a single gene can code for more than one kind of polypeptide

mRNA that has undergone all modifications

mature mRNA

mature mRNA can:

proceed to cytoplasm for translation at the ribosomes

“big picture” of translation

transcription writes down information from the DNA and allows it to leave the nucleus to be translated into a protein

in eukaryotes: newly transcribed RNA molecules that have not yet been processed to mature RNA

primary transcripts

primary transcript of protein-coding genes

• processed to form mRNA

pre-mRNA

changes that a primary RNA transcript undergoes to become a mature RNA molecule

• 5’ cap

• 3’ poly A tail

• intron splicing

RNA processing

where does splicing occur?

• while transcription is still happening

nucleus

small nuclear ribonucleoproteins: any of a class of small RNAs associated with proteins and found in the nucleus of eukaryotic cells, where they form the spliceosome and catalyze splicing

snRNPs

binds to DNA and synthesizes complementary mRNA from it

RNA polymerase

strand read by RNAP

template strand

strand NOT READ by RNAP— is complementary to template strand and matches RNA sequence (besides T → U)

coding strand

general term for the enzyme within a multipart holoenzyme that is responsible for catalysis

core enzyme

a bacterial protein that associates with core RNA pol to allow recognition of promoters

sigma

regions of DNA that allow transcription to start

• bacteria can produce many genes from one

• eukaryotes typically have 1 per gene

promoter

a general term for any multipart enzyme consisting of a catalytic enzyme and other proteins required for function

holoenzyme

targets and silences specific mRNA sequences, ultimately leading to mRNA degradation or translational repression

RISC protein complex