UNIT 2: PROTEIN SYNTHESIS (1)

Two processes of protein synthesis, in order

Transcription, then translation

Where does transcription happen?

Nucleus

Where does translation happen?

Cytoplasm, at a ribosome

Transcription makes ___ from a DNA template.

RNA

Enzyme that builds RNA during transcription

RNA polymerase

DNA region that signals where transcription STARTS

Promoter

DNA region that signals where transcription ENDS

Terminator

Type of RNA that carries the instructions (the 'message')

mRNA (messenger RNA)

Type of RNA that carries amino acids to the ribosome

tRNA (transfer RNA) — Why: Hook: tRNA = Taxi.

Type of RNA that makes up the ribosome

rRNA (ribosomal RNA)

In transcription, DNA base A pairs with RNA base ___.

U (uracil)

In transcription, DNA base T pairs with RNA base ___.

A

DNA template ACGTT → mRNA?

UGCAA

DNA template ATTGCA → mRNA?

UAACGU

Non-coding sections removed from pre-mRNA

Introns — Why: Hook: INtrons = INterruptions.

Coding sections spliced together in mRNA

Exons — Why: Hook: EXons are EXpressed.

Small nuclear proteins that remove introns and splice exons

snRNPs ('snurps')

3-base sequence on DNA

Base triplet

3-base sequence on mRNA

Codon

3-base sequence on tRNA

Anticodon

The tRNA anticodon is complementary to the ___.

mRNA codon

The anticodon has the same letters as the DNA base triplet, except ___.

U replaces T — Why: Because both are complements of the codon.

Start codon, and the amino acid it codes for

AUG; methionine (Met)

Anticodon that pairs with the start codon AUG

UAC

The 3 stop codons

UAA, UAG, UGA — Why: Hook: 'U Are Away, U Are Gone, U Go Away.'

What binds at a stop codon instead of an amino acid?

A release factor

A tRNA with anticodon AGC pairs with which mRNA codon?

UCG

Ribosome site where a NEW tRNA with an amino acid arrives

A site

Ribosome site holding the tRNA with the growing polypeptide

P site — Why: The first tRNA (Met) starts here.

Ribosome site where the empty tRNA EXITS

E site

Base triplet TAC: what is the mRNA codon?

AUG — Why: T→A, A→U, C→G.

Base triplet TAC: what is the tRNA anticodon?

UAC — Why: Complement of codon AUG.

Base triplet TAC: start codon, stop codon, or neither?

Start codon — Why: It becomes AUG.

Base triplet TAC: which amino acid?

Methionine (Met) — Why: NOT Tyr. UAC as a CODON would be Tyr, but here UAC is the anticodon.

Why is 'anticodon UAG' wrong for base triplet TAC?

The codon is AUG, so its complement (anticodon) is UAC, not UAG

DNA template TACGGGCGCTTTATT → mRNA?

AUGCCCGCGAAAUAA

mRNA AUG/CCC/GCG/AAA/UAA → amino acid sequence?

Met-Pro-Ala-Lys (then stop)

In mRNA GGCAUGCAA…, where does translation start?

At AUG (the first 3 bases are skipped)

Can more than one codon code for the same amino acid?

Yes — Why: Example: CCC, CCA, CCG, CCU all = proline.

Point mutation that still codes for the SAME amino acid

Silent mutation

Point mutation that changes ONE amino acid

Missense mutation

Point mutation that creates an early STOP codon

Nonsense mutation

Mutation from inserting or deleting bases that shifts the reading frame

Frameshift mutation — Why: Changes every codon after the mutation.

Why is a frameshift usually worse than a point mutation?

It changes every codon after the mutation instead of just one

Sickle cell disease is caused by what type of mutation?

Missense (point) mutation — Why: Valine replaces glutamic acid at position 6 of hemoglobin.

Multiple ribosomes reading one mRNA at the same time

Polyribosome