Protein Synthesis Quest

review notes, labs (translation webquest)

central dogma of biology

DNA to RNA to protein

gene

section of DNA that codes for one specific protein

amino acid

monomer of protein

polypeptide

chain of bonded amino acids

DNA vs. RNA

DNA is double stranded, deoxyribose, thymine

RNA is single stranded, ribose, uracil

why is RNA used in protein synthesis

DNA is too large to fit through nuclear pores, so RNA carries genetic code out to ribosomes

3 types of RNA

messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA)

messenger RNA

• strand of RNA formed complementary to one strand of DNA

• carries genetic info from DNA in the nucleus to the ribosome in the cytoplasm

• found in nucleus and cytoplasm

ribosomal RNA

• associates with protein to form ribosomes

• found in cytoplasm

transfer RNA

• transports amino acids to ribosome

• found in cytoplasm

ribosome

made up of protein and rRNA, reads mRNA to make proteins

purpose of transcription

first step in making proteins, DNA to mRNA

location of transcription

nucleus

initiation (transcription)

• RNA Polymerase II attaches to promoter (TATA box in eukaryotes) of the gene

• transcription factors mediate binding of RNA polymerase and initiation of transcription

• forms the transcription initiation complex (transcription factors and RNA Polymerase)

elongation (transcription)

• RNA Polymerase II unwinds DNA and separates DNA strands

• base pairing occurs between incoming RNA nucleotides and DNA nucleotides of the gene (template strand)

in what direction does RNA polymerase work

5’ to 3’

termination (transcription)

• RNA Polymerase II continues until it gets to a termination sequence

termination sequence

special sequence that signals the end of a gene, creating a hairpin loop

purpose of mRNA processing (aka splicing)

edit mRNA to have the correct protein sequence before leaving the nucleus; pre-mRNA to mature mRNA (only in eukaryotes)

location of splicing

nucleus

pre-mRNA

original sequence of RNA created from transcription

mature mRNA

result of splicing, end product that goes to the ribosome

intron

non-coding section

exon

coded section for protein

5’ cap

single G nucleotide; helps mRNA bind to the ribosome

Poly-A Tail

50-250 adenine nucleotides; keeps mRNA stable and protects against exonuclease enzymes

what happens during splicing

introns removed, 5’ cap and Poly-A tail added to the ends of the sequence

alternative splicing

rearranges exons in different ways to produce different proteins from the same gene

purpose of translation

to decode RNA and produce specific proteins; RNA to protein

location of translation

cytoplasm

monomer of a protein

amino acid

polypeptide

chain of amino acids

type of bond connecting amino acids

peptide bond

how are peptide bonds formed?

dehydration synthesis

how many different amino acids?

20 (10 from body, 10 from food)

protein folding (sequence)

1. primary structure (amino acid chain)

2. secondary structure (helix)

3. tertiary structure

4. quarternary structure (2 or more polypeptides)

subunits of a ribosome

large subunit and small subunit

what is ribosome made out of

protein and rRNA

groove sites of large subunit

E, P, A

A site

“arrival”; initial binding site for tRNA molecules

P site

“polypeptide”; contains growing polypeptide chain as amino acids link and form peptide bonds; initial binding site for the FIRST tRNA molecule

E site

“exit”, site where tRNA exits once it’s delivered its amino acid

initiation (translation)

• two ribosomal units come together at 5’ end of mRNA

• ribosome reads mRNA in 5’ to 3’ direction until it reaches the start codon

• first tRNA binds to P site

codon

group of 3 nucleotides on mRNA that codes for one amino acid

how many different codons

64 (only 61 code for amino acids)

start codon

AUG, codes for methionine

anticodon

3 nucleotides complementary to a specific codon carrying amino acid specified by codon

what do anticodons code for

nothing

codon recognition

next tRNA anticodon hydrogen bonds to the mRNA codon in the A site

bond formation

amino acid in the P site forms a peptide bond with the amino acid in the A site

translocation

ribosome shifts and the tRNA from the P site enters the E site to leave

termination

• elongation repeats until stop codon reached

• release factors attach to mRNA strand in A site and releases polypeptide strand

• all components detach from one another and reused

stop codon

UGA, UAA, UAG; do not code for amino acids

protein synthesis in eukaryotes vs. prokaryotes

in eukaryotes, transcription occurs in the nucleus and translation occurs in the cytoplasm; in prokaryotes, there is no mRNA processing and transcription and translation occur simultaneously in the cytoplasm