Cell Bio Exam 3

Question 1

Explain what “crossing over” is in relation to the gene and the chromosome. How is the frequency of a “crossing over” event determined?

Answer 1

The positions of the genes along the chromosome (loci) can be mapped in order along the length of chromosomes based on the crossing over rate. The longer the distance between two loci, the HIGHER the crossing over rate.

Question 2

The building blocks of a nucleotide are?

Answer 2

A pentose sugar, a phosphate group, and a nitrogenous base.

Question 3

Where does the information encoded in a DNA nucleotide reside in?

Answer 3

The DNA Base Sequence.

Question 4

What are different versions of a gene called?

Answer 4

Alleles

Question 5

A single gene can encode a number of related proteins as a result of a process called…

Answer 5

Alternative splicing

Question 6

Single-stranded DNA molecules are capable of re-associating with correct base pairing when temperature decreases gradually. What is this property referred to as?

Answer 6

DNA renaturation

Question 7

What enzyme is responsible for synthesizing mRNAs in the eukaryotic organisms?

Answer 7

RNA polymerase II

Question 8

What is NOT a normal property of eukaryotic mRNAs?

Answer 8

They reside in the nucleus.

Question 9

The macromolecular complex that associates with each intron and splices it is called…

Answer 9

Spliceosome

Question 10

There is only one factor that possesses enzymatic activity in the preinitiation complex for RNA polymerase II. The factor is?

Answer 10

TFIIH

Question 11

A mature mRNA DOES NOT contain…

Answer 11

Introns

Question 12

A tRNA has an anticodon with the sequence 5-AUG-3. What would be the sequence of the complementary codon to the normal base pair rule?

Answer 12

3’-UAC-5’

Question 13

Based on the interchangeability of the nucleotide in the third position. Francis Crick proposed that the same tRNA may be able to recognize more than one codon. What was his proposal called?

Answer 13

The Wobble Hypothesis

Question 14

What enzyme is responsible for the activation of amino acids?

Answer 14

Aminoacyl-tRNA synthetase

Question 15

Which of the following is not required for protein synthesis?

Answer 15

Gerneral Transcription Factors

Question 16

The amino acid bound to the A site tRNA linked to carboxyl carbon of the amino acids are bound to the P site tRNA through?

Answer 16

Peptidyl bonds

Question 17

What is the significance of the variability of the third nucleotide in a codon?

Answer 17

The same tRNA can recognize more than one codon.

Question 18

Where does the tRNA bind to during the initiation of protein synthesis?

Answer 18

During initiation of protein synthesis, initiation tRNA binds to “P site” of the ribosome.

Question 19

The specific site on the bacterial chromosome at which replication begins is called the?

Answer 19

Origin

Question 20

Replication moves outward from the origin in “___” directions and is said to be “_______”.

Answer 20

1) both

2) Bidirectional

Question 21

What DNA molecule could serve as an effective template for DNA synthesis?

Answer 21

a partially double-stranded DNA

Question 22

All DNA polymerases lay down nucleotides in a “______” direction and move along the template in a “_______” direction.

Answer 22

1) 5-3

2) 3-5

Question 23

The DNA strand growing toward the replication fork grows “________” in a 5-3 direction as the replication fork advances and is called the “_________”.

Answer 23

1) continuously

2) leading strand

Question 24

During replication, DNA is constructed in small segments call “_______” that are rapidly linked to longer pieces of DNA synthesized earlier.

Answer 24

Okazaki fragments

Question 25

Strand initiation during replication is carried out by an enzyme that makes a short RNA molecule that is used as a primer; the enzyme is a distinct type of RNA polymerase called?

Answer 25

Primase

Question 26

Which of the following may be a further advantage of using RNA primers during initiation of a stand in a replication?

Answer 26

Using primers may decrease mistakes; such errors as mismatched...

Question 27

What proteins bind selectively to single-stranded DNA and are responsible for keeping it extended and preventing it from being rewound?

Answer 27

Single-standed DNA binding (SSB) proteins

Question 28

What is the function of the 5`----3` exonuclease activity of DNA polymerase?

Answer 28

It removes the RNA primer laid down by the primase at the 5` end of the Okazaki fragment.

Question 29

What is the advantage of transcription-coupled repair?

Answer 29

It ensures that the genes of the greatest importance to the cell receive the highest priority on the repair list.

Question 30

What must the mismatch repair system be able to distinguish in order to tell which nucleotide of a mismatched pair to replace?

Answer 30

It must be able to distinguish the newly made strand from the parental strand.

Question 31

Describe what a promoter is and what function it possesses.

Answer 31

A promoter is a region of DNA located upstream of the transcription start site. It has 2 functions: 1) It determines which DNA strand will serve as the template and where transcription will begin 2) It initiates transcription.

Question 32

List the contents of Mendel's Law.

Answer 32

Law of Segregation: states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization Law of Independent Assortment: states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.

Question 33

Please describe what the functions for the 5` cap and 3` poly A tails.

Answer 33

5' Methylguanosine cap functions: - prevents 5' end of mRNA from being digested by enzymes - plays an important role in initiating translation - aids in transporting mRNA out of the nucleus 3' Poly A tail functions: - Protects the mRNA from premature degradation by enzymes

Question 34

List the mutations that can occur in codons.

Answer 34

- A single nucleotide mutation 1) Synonymous: DNA mutation does not change the amino acid sequence 2) Non-synonymous: DNA mutation causes an amino acid substitution 3) Nonsense: DNA mutation creates a premature termination codon - Insertion or deletion mutation: 1) one or more nucleotide(s) 2) A frameshift DNA mutation alters the normal frame of the mRNA

Question 35

List enzymes required for DNA replication and their functions.

Answer 35

DNA Helicase: Unwinds the DNA double helix DNA Primase: synthesizes RNA primer DNA Polymerase: Synthesizes new DNA strand DNA Ligase: joins fragmented DNA together DNA Topoisomerase: Changes the supercoiled state of the DNA duplex

Question 36

According to Watson-Crick Proposal, DNA possesses specific properties. Please list at least 6 properties that were proposed in that proposal. (There are 11 in total to pick from)

Answer 36

1. DNA is made of two chains of nucleotides 2. The two chains spiral around each other to form a pair of right-handed helices 3. The two chains are ANTIPARALLEL (they run in opposite directions) 4. The sugar-phosphate backbone is found on the outside of the molecule and the bases are inside the helix 5. The double helix is 2 nm wide 6. The DNA chains are held together by hydrogen bonds between each base 7. Pyrimidines are always paired with purines 8. Only A-T and C-G pairs fit within the double helix 9. DNA molecule has a major groove (wider) and a minor groove (more narrow) 10. The double helix makes a complete turn every 10 residues (3.4 nm) 11. The two chains are COMPLEMENTARY to each other

Question 37

Describe the key steps and the key events of each step in the translation procedure of eukaryotic cells.

Answer 37

Translation happens in three steps: 1) Initiation - 43S Complex (small subunit) binds to 5' end of mRNA complex and scans for the AUG start codon - The 60S (large subunit) joins in after 43S complex reaches the appropriate AUG codon 2) Elongation - Aminoacyl-tRNAs are selected - Peptide bonds are formed - Translocation (the procedure where the ribosome moves of one codon in the 5' to 3' direction on the mRNA) happens - The deacetylated tRNA is released 3) Termination - happens when one of three stop codons appear - needs release factor eRF1 to recognize the stop codons - accompanied by the disassociation of the mRNA from the ribosome and the disassembly of ribosome