Chapter 10 - DNA Structure

Question 1

What are the 4 requirements for genetic material?

Answer 1

Contain complex information

Replicate faithfully/accurately

Encode the phenotype

Have the capacity to vary

Question 2

What did Miescher discover?

Answer 2

Nuclein (DNA) in the nuclei of white blood cells

Question 2

What did Kossel discover?

Answer 2

Nitrogenous bases (A, C, T, and G)

Question 2

What did Levene discover (2)?

Answer 2

Nucleotides - made up of a sugar, phosphate, and base

Tetranucleotide hypothesis - thought all 4 bases were contained in each nucleotide (disproven by Chargaff)

Question 3

What did Hershey-Chase discovery (1) and what was the experiment (7)?

Answer 3

Discovered that DNA is the genetic material in bacteriophages

Experiment:
1. Wanted to determien whether phage protein or DNA was transmitted during phage reproductive cycle
2. Tagged proteins with sulfur isotope and DNA with phosphorous isotope to follow isotopes through life cycle
3. Grew E. coli in each medium and infected them with type II bacteriophage
4. Bacteria took up tagged phages, which allowed them to replicate and spread phages
5. Looked at empty protein coats and saw that there was sulfur isotope but no phosphorous isotope
6. Could also see that phosphorous isotope was in genetic material being transmitted through life ycle
7. Detemined that protein did not get transmitted to bacteria in life cycle and the DNA of the phage is passed into the bacteria

Question 3

What did Griffith discover (1) and what was his experiment (4)?

Answer 3

Discovered transformation principle - bacteria will take up DNA from the media it’s growing in

Experiment:
1. Took virulent and nonvirulent bacteria and killed some of them, grew it on a media, and injected it into a mouse
2. Found that with virulent bacteria, mouse died
3. Nonvirulent bacteria, mouse lived
4. Mixture of heat killed bacteria and nonvirulent bacteria - mouse died because heat killed bacteria took up DNA of virulent bacteria

Question 3

What did Avery, MacLeod, and McCarty discover (1) and what what their experiment (4)?

Answer 3

Discovered that the transforming substance is DNA

Experiment:
1. Took homogenates of heat killed virulent bacteria and treated samples with enzymes that destroys proteins (protease), RNA (RNase), or DNA (DNase)
2. Added sample to type IIR bacteria
3. Found that cultures treated with protease or RNase contained transformed type IIIS bacteria but the culture treated with DNase did not
4. Conclusion - Because only DNase destroyed the transforming substance, the transforming substance is DNA

Question 3

What did Rosalind Franklin and Watson/Crick discover (2)?

Answer 3

Produced high quality images of the structure of the DNA molecule through x-ray crystallography

Watson and Crick used images to determine the double helix molecule structure of DNA

Question 4

What did Fraenkel-Conrat and Singer discover?

Answer 4

RNA carries genetic information in the tobacco mosaic virus

Question 5

What is the primary structure of DNA/RNA (8)?

Answer 5

Sugar - pentose sugars
- Ribose (RNA) has OH group on 2’ carbon, making it very unstable
- Deoxyribose (DNA) has H on 2’ carbon

Nitrogenous base
- Purines: double ring (adenine and guanine)
- Pyrimidines: single ring (cytosine, thymine, and uracil)

Phosphate group - confers negative charge and acidity to DNA molecule
- Always bonded to 5’ carbon

Question 6

What is a nucleoside?

Answer 6

Sugar and base together

Question 7

What is Chargaff’s rule?

Answer 7

The amount of A should equal T and the amount of C should equal G

Question 8

How do you determine whether a strand is double or single stranded?

Answer 8

Number of A = T and C = G: double stranded

Not equal: single stranded

Question 9

How is a single strand of DNA or RNA bonded together (3)?

Answer 9

Phosphodiester linkages
- Connects 5’ phosphate group and the 3’ OH group of adjoining nucleotides
- Results in alternating structure of phosphate and sugar groups for both DNA and RNA

Question 10

How do DNA strands appear (2)?

Answer 10

Run antiparallel to each other

Strand runs 5’ to 3’, so 5’ end should always have a free phosphate and 3’ end should always have a free sugar

Question 11

How are strands connected (3)?

Answer 11

Hydrogen bonds between respective base pairings

A-T has 2 hydrogen bonds

C-G has 3 hydrogen bonds

Question 12

What does it mean for strands to be complementary?

Answer 12

Strands don’t have the same base pair sequence, but the sequences are complementary to each other because they have the opposite base pairs (A/T, C/G)

Question 13

What are the 3 forms of DNA and how are they distinguished?

Answer 13

B form - what we see under most cellular conditions; most stable configuration of DNA
- Right handed helices
- 10-12 base pairs per rotation
- Slim and elongated structure
- Major and minor grooves where different proteins will bind (important for gene expression)

A form - similar to B form
- Shorter and wider
- Bases tilt away from main axis

Z form
- Left handed helices
- Sugar-phosphate backbone zignags as it goes around axis

Question 14

What are the 3 secondary structure rearrangements that can happen in DNA/RNA?

Answer 14

Hairpins

Triple DNA (HDNA)

DNA methylation

Question 15

What are hairpins?

Answer 15

• DNA base pairs on the same strand that are inverted complements of each other
• Strand bends and complements bonds with each other to form stems and loops
• Form a lot in RNA secondary structures and play a large role in RNA function

Question 16

What is triple DNA (HDNA)?

Answer 16

• Three nucleotide strand
• Single strand of one DNA molecule binds with another double strand of DNA

Question 17

What is DNA methylation?

Answer 17

• Modification of primary structure of DNA in which a methyl group is added to certain positions of nitrogenous bases
• Decreases level of transcription - effects levels of gene expression
• Can alter 3D structure of DNA
• Prokaryotes tend to be T and G
• Eukaryotes tend to be A and C

Question 18

What are the 3 types of DNA sequence variations?

Answer 18

Unique

Moderately repetitive - tandem or interspersed

Highly repetitive

Question 19

What are unique DNA sequences?

Answer 19

Sequences present only one or a few times in the entire genome

Primarily protein coding sequences

Question 20

What are gene families?

Answer 20

Unique DNA sequences present a few times with some small changes

Have similar structure and function, but not identical

Question 21

What are moderately repeditive DNA sequences and its two sub-variations?

Answer 21

Sequences of 150-300 base pairs that are repeated thousands of times in the genome

Tandem - repetitive sequences right next to each other
- Tend to be clustered in the same part of chromosomes

Interspersed - repeats that are scattered throughout the genome
- SINES - short interspersed repeats
- LINES - long interspersed repeats

Question 22

What are highly repetitive DNA sequences?

Answer 22

Sequences of 10-20 base pairs long that are repeated millions of time tandem and interspersed throughout the genome

Common in centromeres and telomeres of chromosomes

Rarely transcribed, so we don’t know their function

Question 23

What is cytoplasmic DNA?

Answer 23

DNA not contained in the nucleus

DNA within mitochondria and chloroplasts

Question 24

What are the 5 characteristics of cytoplasmic DNA?

Answer 24

Ring of double-stranded DNA
- Outer strand is H strand
- Inner strand is L strand

Evidence for endosymbiotic theory

Mostly uniparentally inherited - through mother

Replicative segregation - replicate and randomly segregate into daughter cells

Highly organized and some very important genes for cellular function are encoded (ex: production of ATP)

Question 25

What is the central dogma and its pathway?

Answer 25

How genetic information flows through a cell from DNA to protein

Pathway:
- How DNA is replicated
- How information is transcribed from DNA to RNA
- How information is translated from RNA to protein