Gene Expression

Question 1

A copy of the entire genome is how many base pairs

Answer 1

3 million

Question 2

Exons contain __

Introns contain __

Answer 2

Exons contain RNA information that produce RNA and proteins.

Introns stay in the nucleus and contain information to regulate the expression of the gene.

Question 3

Protein synthesis =

Answer 3

gene expression

Question 4

The template strand is called the

Answer 4

Anti-sense

RNA is complementary to this strand.

Question 5

The coding strand is called the

Answer 5

Sense strand

RNA is almost identical to this strand, with the exception of uracil instead of thymine.

Question 6

What occurs during the initiation phase of transcription

Answer 6

Histones are acetylated, which makes them unwind so that the DNA is accessible for GTFs. GTFs will bind to the promotor sequence of a gene (TATA) that is upstream from the transcription start site. GTF then signal RNA pol II to come bind to the promotor sequence.

Question 7

What occurs during the elongation phase of transcription

Answer 7

RNA pol II reads DNA from 3-5, but adds 5-3. adds complementary base pairs to the 3’ end of the growing RNA.

Question 8

How does elongation end (termination) of transcription?

Answer 8

Elongation ends with RNA pol II reaches the terminal sequence of the gene.

Question 9

How is mRNA modified before leaving the nucleus

Answer 9

1. GTP is added to the 5’ end (5’ cap) This prevents degradation and permits initiation of translation.
2. adenine nucleotides are added to the 3’ end. Protects from degradation.
3. Splicing occurs by splicosomes (Small nuclear RNA and small nuclear ribonucleic protein- AKA snRNA and snRNPs)

Question 10

What proteins make up the spliceosome

Answer 10

small nuclear RNA (snRNA) and small nuclear ribonucleic protein (snRNPs)

Question 11

How many amino acids- how many start, stop, and regular?

Answer 11

64 total
3 start
1 stop
61 other

Question 12

Codons are ___, ___, and ___

Answer 12

Universal (with the acceptation of a few single cell organisms)

unambiguous (1 codon translates to only 1 specific AA)

Degenerate/redundant (UUU and UUC both translate to the same AA)

Question 13

How is translation initiated?

Answer 13

The small ribosomal subunit binds to the 5’ GTP cap of the mRNA strand and scans the mRNA until it reaches the start codon, which is AUG. Initiation factors then recruit tRNA to the site of translation. Once tRNA binds to the P spot, the large ribosomal subunit joins.

Question 14

Sites in the large ribosomal subunit

Answer 14

E- exit
P- Peptidyl site. tRNA in this site contains a growing polypeptide chain.
A- Aminoacyl site. tRNA in this site contain a new amino acid that needs to be joined to the growing chain.

The first tRNA that codes for start begins in the P side. Another tRNA will join in the A site. The start AA will be transferred on top of the AA in the A site and they will both slide over. So now the first tRNA is in the E site, ready to exit, and the tRNA with 2 amino acids is in the P site. Now the A site is empty for another tRNA to come in.

Question 15

tRNA in the P site breaks its bond with its amino acid, releasing energy. This allows a peptide bond to be formed between the amino acids just released and the amino acid attached to the tRNA in the A site. This is catalyzed by which enzyme?

Answer 15

Catalyzed by rRNA (ribozyme)

rRNA can be an emzyme, but it is NOT a protein.

Question 16

Termination of translation

Answer 16

Elongation ends with a stop codon is reached. A releasing factor binds to the stop codon in the A side and the polypeptide is released and then ribosomal subunit disassembles.

mRNA is available to be translated again if needed

Question 17

Codons must be read in which direction?

Anticodons must be described in which direction?

Answer 17

Codons are read by the ribosome in the 5’-3’ direction.

Anticodons must be described in the 5’-3’ direction as well.

Question 18

During translation, what changes are typically made?

Answer 18

Methionine is usually acetylated. 80-90% of proteins have the first amino acid acetylated. Significance is unclear

Question 19

After translation, how can polypeptides be modified?

Answer 19

1. Carbohydrates could be added. Glycosylation.
2. Lipids may be added Increase hydrophobicity.
3. Phosphate groups may be added- plays critical role in cellular regulation.
4. Methyl groups may be added to increase hydrophobicity or if bound to histones, will inhibit transcription
5. Acetyl groups. plays a role in regulating gene expression.
6. Peptide bonds may be cleaved. Could be because the protein needs to be degraded if it was misfiled or unneeded. Or it could be cleaved to activate it (zymogens are cleaved to become active enzymes).

Question 20

What happens if histones are methylated

Answer 20

They are tightly packed and cannot be transcribed.

Question 21

What occurs if a polypeptide is destined for the ER, golgi, lysosome, cell membrane, or exterior of the cell?

Answer 21

After translation, it will head to the ER for foldings and modification. It will then be transported to the golgi, where it will undergo more processing. From the golgi, proteins are transported in vesicles to lysosomes, the cell membrane, exterior of the cell, back to the ER, or stay in the golgi.

Question 22

What occurs if a polypeptide is destined for the nucleus, mitochondria, or peroxisomes?

Answer 22

After translation, a targeting signal on these polypeptides will indicate where they go. If they do not have a targeting signal, they will remain in the cytoplasm (default destination).