Chapter 10

Question 1

Even before nucleic acids were identified as the genetic material, it was understood that:

Answer 1

1.Genetic material must contain complex information.

2.Genetic material must replicate faithfully.

3.Genetic material must
encode the phenotype.

4.Genetic material must
have the capacity to vary

Question 2

The Hershey-Chase Experiment

Answer 2

Used T2 bacteriophage (virus that infects bacteria) to observe phage replication.

Question 3

Watson and Crick’s discovery

Answer 3

Watson and Crick applied laws of structural chemistry to Franklin’s images to identify 3D structure of DNA.
Watson realized A could bind with T and G with C!
Accounted for Chargaff’s base ratios!

Question 4

Tobacco mosaic virus

Answer 4

Single molecule of RNA surrounded by a helically arranged cylinder of protein molecules.

Singer and Fraenkel-Conrat created hybrid viruses by mixing RNA and protein from different strains of TMV and produced new viral particles!

Question 5

Three levels of DNA structure

Answer 5

Primary structure

Secondary structure – stable three-dimensional configuration (helical structure worked out by Watson/Crick)

Tertiary structures – the complex packing arrangements of double-stranded DNA In chromosomes

Question 6

Primary structure –

Answer 6

nucleotide structure and how the nucleotides are joined together

consists of a string of nucleotides joined together by phosphodiester linkages

DNA is fairly simple – a chain (polymer) of many repeating nucleotide units.
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Question 7

Nucleotides consist of three main parts:

Answer 7

Sugar
Phosphate group
Nitrogen-containing base

Question 8

Sugars

Answer 8

The sugars in DNA and RNA are slightly different in structure.

Ribosome and Deoxyribose

Question 9

Nitrogen Bases

Answer 9

Purine: Bigger, Adenine (A) and Guanine (G)

Pyrimidine: Smaller Cytosine (C), Thymine(T) (DNA), Uracil (U) (RNA)

Question 10

Phosphate group

Answer 10

Found in every nucleotide

Frequently carry a negative charge,
making DNA acidic.

Always bound to the 5’– carbon atom
of the sugar.

Question 11

Polynucleotide Strands

Answer 11

Nucleotides connected by covalent bonds.

5’-phosphate group to the 3’-hydroxyl group

phosphodiester linkages – strong covalent bonds.

A series of these nucleotides = polynucleotide strand.

Question 12

Double helix

Answer 12

Two polynucleotide strands

Sugar-phosphate linkages are on the outside

Bases are stacked in the interior of the molecule

The two strands are antiparallel - run in opposite directions
5’ end of one strand is opposite 3’ end of the other

Question 13

Hydrogen bond imposes a limitation on bases that can pair.

Answer 13

3 H bonds between C -G
2 H bonds between A - T

This gives the the characteristic of complementary DNA strands – a critical feature for efficient DNA replication

Stacking pattern helps to stabilize the DNA molecule.

Question 14

C-G pairing is_______than A–T pairing

Answer 14

stronger

Question 15

DNA methylation:

Answer 15

Methyl groups (CH3)added to nucleotide bases
Related to gene expression in eukaryotes
Affects the three-dimensional structure of DNA

Question 16

H-DNA:

Answer 16

three-stranded (triplex); formed when DNA unwinds and one strand pairs with double-stranded DNA from another part of the molecule

Long sequences of only purines or only pyrimidines

H-DNA breaks more readily than double-stranded DNA

Question 17

RNA molecules may contain numerous hairpins, allowing them to

Answer 17

fold up into complex structures.

Question 18

DNA normally consists of two polynucleotide strands that are

Answer 18

antiparallel and complementary.

Question 19

B-DNA

Answer 19

Three-dimensional structure identified by Watson and Crick refers to B-DNA

Plenty of water
No unusual base sequences
Most stable configuration
Predominant

Question 20

A-DNA

Answer 20

Exists if less water is present

Right-handed helix

Shorter and wider

Base pairs are tilted away from the main axis

Detected in some DNA-protein complexes and in spores of some bacteria.

Question 21

Z-DNA

Answer 21

• Radically different in structure
  Left-handed helix

Sugar-phosphate backbone zigzags back and forth

Can result if the molecule contains particular base sequences (i.e. stretches of alternating C and G nucleotides).

May play a role in gene expression

Question 22

Hairpin structure

Answer 22

In single strands of nucleotides, when sequences of nucleotides on the same strand are inverted complements, a hairpin structure will be formed.

Question 23

If complementary sequences are contiguous (close together/touching), the hairpin has a _____ but no _____

Answer 23

stem,loop