CH7 RNA and the Genetic Code

Question 1

• mRNA (polymerase 2) (what is hnRNA)
• tRNA (Polymerase 3
• rRNA (Polymerase 1 and 3 )

Answer 1

• mRNA: Transcribed from template DNA by RNA polymerase enzymes. Takes info to ribosomes to make proteins. hnRNA is mRNA before it is spliced
• tRNA: Folded RNA strand with a 3 nucleotide anti-codon and with amino acid attacched
• rRNA: Synthesized in the nucleolus. Some function as ribozymes and help catalyze the formation of peptide bonds

Question 2

Degeneracy and wobble

Point mutations

1. Missense mutation:
2. Nonsense mutation:

Frameshift mutations

1.

Answer 2

1 AA can by specified by multple codons, the first 2 bases are usually the same.

3rd one is variale = in wobble postion and if affected it will be a silent/degenerate mutation. bc it will still code for that AA

i.e glycine is coded by GG and third can be A, C, G, or U

Point mutations

1. Missense mutation: Substitution of a codon which cause substitution of AA
2. Nonsense mutation: It changes that codon to a stop codon = stops prematurely also called truncation mutation

Frameshift mutaiton: Nucleotides are added or deleted

Question 3

Splicing: Introns and exons

Alternative Splicing

5’ Cap

3’ Tail

Answer 3

Spliceosome splices the hnRNA and removes the introns and ligates the exons together

Alternative Splicing: Allows for the making of many different proteins from the same gene

At the 5’ end a triphosphate cap is added to be recognized for the ribosome as the binding site

At the 3’ a polyadenosyl tail is added to protect from rapid degradation in the cytoplasm

Question 4

Translation:

Need energy? peptidyl transferase

1. Initiation
2. Elongation
3. Termination

Answer 4

All stages require energy

peptidyl transferase: catalyzes peptide bond formation b/w incoming amino acid to A site with the growing amino chain on the P site

1. Initiation
2. Elongation
3. Termination

Question 5

Posttranslational processing

1. Phosphorylation
2. Carboxylation
3. Glycosylation
4. Prenylation

Answer 5

1. Phosphorylation: Adding phosphate group (PO4-2) to activate or deactivate proteins
2. Carboxylation: Adding carboxylic acid, usually to serve as calcium biding sites
3. Glycosylation: Addition of oligosaccharides in the ER and Golgi apparatus to determine cellular destination
4. Prenylation

Question 6

Prokaryotic gene regulation:

what is the promotor and operator

The Lac operon (positive control)

Trp operon (negative control)

Answer 6

Promotor = Where RNA polymerase binds

Operator = the door that allows RNA polymerase to move. It can be locked by the repressor

The Lac operon: no lactose = repressor on, lactose binds and allows RNA polymerase to transcribe mRNA

Trp: Trp presents = repressor on

Question 7

• Eukaryotic Gene Regulation
• Enhancers and transcription factors
• Histone Acetylation and Deacetylases
• DNA Methylation
• Heterochromatin vs Euchromatin regions

Answer 7

• Prior to the promotor, there are enhancers in the DNA where transcription factors can bind. They enhance the activity of RNA polymerase at a single promotor site
• DNA bends and allows RNA polymerase to start transcription
• Histone Acetylation: Decreases + charge of lysine residues and weakens the interaction of the histone with DNA. Deacetylases remove acetyl groups and close the chromatin to reduce transcription
• DNA Methylation: Adds methyl groups to cytosine and adenine to silence the gene expression
• Heterochromatin: Tightly coiled DNA appears dark under microscope usually inactive genes that are highly methylated