RNA AND THE GENETIC CODE

Central Dogma

DNA -> RNA -> Protein

Dengenerate code

allows multiple codons to encode for the same amino acid

Initiation

AUG (methionine)

Termination

UAA, UGA, UAG

What do redundancy and wobble allow mutations?

to occur without affecting the protein

Wobble

third base in a codon

Point mutations can cause

- silent mutations

- nonsense mutation

- missense mutations

- frameshift mutations

Silent mutations

with no effect on protein synthesis

Nonsense mutation (truncation)

mutations, which produce a premature stop codon

Missense mutation

mutations, which produce a codon that codes for a different amino acid

Frameshift mutation

which result from nucleotide addition or deletion and change the reading frame of subsequent codons

RNA is structurally similar to DNA except:

-Substitution of a ribose sugar for deoxyribose

-Substitution of uracil for thymine

-Single-stranded instead of double-stranded

What are the 3 major types of RNA in transcription?

-messenger RNA (mRNA)

-transfer RNA (tRNA)

-ribosomal RNA (rRNA)

What does messenger RNA (mRNA) carry?

message from the DNA in the nucleus

What process involves the transcription of the gene?

creation of messenger RNA (mRNA)

Where does mRNA travel after being transcribed?

into the cytoplasm

What happens to mRNA in the cytoplasm?

it is translated

Transfer RNA (tRNA)

brings amino acids; recognizes the codon on the mRNA using its anticodon

Ribosomal RNA (rRNA)

makes up much of the ribosome; enzymatically active

What enzymes unwind the DNA double helix during transcription?

Helicase and topoisomerase

Where does RNA polymerase II bind during transcription?

To the TATA box within the promoter region of the gene

What type of RNA is synthesized from the DNA template (antisense) strand during transcription?

hnRNA (heterogeneous nuclear RNA)

What is added to the 5' end during posttranscriptional modifications?

7-methylguanylate triphosphate cap

What is added to the 3' end during posttranscriptional modifications?

Polyadenosyl (poly-A) tail

What is the role of the spliceosome in posttranscriptional modifications?

It removes introns and ligates exons together.

What is alternative splicing?

It combines different exons to acquire different gene products.

Where does translation occur?

ribosome

What are the 3 stages of translation?

initiation, elongation, termination

What is the role of chaperones in posttranslation modifications?

Folding of proteins

What is the formation of quaternary structure in proteins?

The assembly of multiple polypeptide chains into a functional protein complex

What is the purpose of cleavage in posttranslation modifications?

Cleavage of proteins or signal sequences

What is phosphorylation?

A covalent addition of a phosphate group to a biomolecule

What is carboxylation?

A covalent addition of a carboxyl group to a biomolecule

What is glycosylation?

A covalent addition of sugar molecules to a biomolecule

What is prenylation?

A covalent addition of lipid groups to a biomolecule

Control of Gene Expression in Prokaryotes

Operons (Jacob-Monod model)

Operons (Jacob-Monod model)

are inducible or repressible clusters of genes transcribed as a single mRNA

Control of Gene Expression in Eukaryotes

transcription factors search for promoter and enhancer regions in the DNA

Promoters

are within 25 base pairs of the transcription start site

Enhancers

are more than 25 base pairs away from the transcription start site

Nonsense mutation (truncation)