Biochemistry Chapter 6: DNA and Biotechnology

Question 1

What do nucleosides contain?

Answer 1

5-C sugar bound to a nitrogenous base

Question 2

What is a nucleotide?

Answer 2

A nucleoside with 1 to three phosphate groups added.

Question 3

Difference in nucleotides between DNA and RNA?

Answer 3

Deoxyribose vs. Ribose

Question 4

What are the 5 types of nucleotides?

Answer 4

Adenine
Cytosine
Guanine 
Thymine
Uracil

Question 5

How is DNA organized?

Answer 5

• read 5’ to 3’
• antiparallel strands
• purines pair with pyrimidines (A-T(U)) (G-C)

Question 6

How many bonds between A and T, G and C?

Answer 6

A - T = 2 bonds

G - T = 3 bonds

Question 7

What does it mean that purines and pyrimidines are aromatic heterocycles?

Answer 7

cyclic, planar and conjugated

contain 4n + 2 pi electrons where n is any integer. At least two different elements in the ring

Question 8

What is Chargaff’s rule?

Answer 8

purines and pyrimidines are equal in number in a DNA molecule and that because of base-pairing, the amount of A = T and G = C

Question 9

What type of helix is most DNA?

Answer 9

B-DNA - forming a right hand helix. When high G-C content or high salt concentration, may see zigzag Z-DNA

Question 10

What can cause denaturation of DNA?

Answer 10

Heat alkaline pH, chemicals

Question 11

How many chromosomes are there?

Answer 11

46 - 44 autosomes and 2 sex chromosomes

Question 12

What is DNA stored in?

Answer 12

Histone proteins (H2A, H2B, H3 and H4) – histones make nucleosomes, make up chromatin

Question 13

Heterochromatin

Answer 13

dense, transcriptionally silent, appears dark

Question 14

Euchromatin

Answer 14

less dense and transcriptionally active

Question 15

Telomeres

Answer 15

contain high GC content to prevent unraveling - shortened during replication - prevent against molecular aging

Question 16

Centromeres

Answer 16

Located in the middle of chromosomes and hold sister chromatids together until they are separated during anaphase in mitosis.

Question 17

What is the replisome?

Answer 17

a set of specialized proteins that assist the DNA polymerases

Question 18

How are single strands kept from reannealling?

Answer 18

single-stranded DNA-binding proteins

Question 19

What creates nicks in the DNA to help alleviate supercoiling tension?

Answer 19

DNA topoisomerase II (DNA gyrase)

Question 20

What puts down a small RNA primer?

Answer 20

primase

Question 21

What does DNA polymerase III (pro) or alpha and delta (euk) do?

Answer 21

synthesizes a new strand of DNA - read 3’ to 5’ and write 5’ to 3’

Question 22

What removes DNA primers?

Answer 22

DNA polymerase I (prok) or RNase H (euk)

Question 23

What does ligase do?

Answer 23

fuses DNA strands together

Question 24

What do oncogenes develop from?

Answer 24

mutations of protooncogenes and promote cell cycling. May lead to cancer.

Question 25

What are tumor suppressor genes?

Answer 25

code for proteins that reduce cell cycling or promote repair

Question 26

What is a mismatch repair?

Answer 26

Occurs during the G2 phase using the genes MSH2 and MLH1

Question 27

What is a nucleotide excision repair?

Answer 27

fixes helix-deforming lesions of DNA, via a cut and patch process that requires and excision exonuclease.

Question 28

What is a base excision repair?

Answer 28

fixes nondeforming lesions of the DNA helix by removing the base, leaving a apurinic/apyrimidinic site. An AP endonuclease removes the damaged sequence, which can be filled in with the correct bases.

Question 29

What is recombiant DNA?

Answer 29

DNA composed of nucleotides from 2 different sources.

Question 30

What is cloning?

Answer 30

introduces a fragment of DNA into a vector plasmid. A restriction enzyme cuts the plasmid and DNA, leaving sticky ends. Once the fragment binds, it can be introduced into a bacteria cell.

Question 31

Vectors contain:

Answer 31

an origin of replication, fragment of interest, and at least 1 gene for antibiotic resistance

Question 32

What are cDNA libraries?

Answer 32

contain smaller fragments of DNA and only include the exons of genes expressed by the sample tissue. They can be used to make recombinant proteins or for gene therapy.

Question 33

What is PCR?

Answer 33

an automated process by which millions of copies of a DNA sequence can be created from a very small sample by hybridization.

Question 34

How can DNA molecules be separated?

Answer 34

agarose gel electrophoresis

Question 35

Southern blotting

Answer 35

Can be used to detect the presence and quantity of various DNA strands in a sample. After electrophoresis, the sample is transferred to a membrane that can be probed.

Question 36

How do you do DNA sequencing?

Answer 36

uses dideoxyribonucleotides to terminate the DNA strand because they lack the 3' OH group.

Question 37

What is gene therapy?

Answer 37

method of curing genetic deficiencies by introducing a functional gene with a viral vector

Question 38

Chimera

Answer 38

contain cells from two different lineages

Question 39

What is a knockout?

Answer 39

deleting a gene of interest