Genetics Chapter 9

Main structural features of B DNA?

- 10 base-pairs per turn - Bases are aligned perpendicualr to the central axis of the molecule

tRNA molecules are good examples of RNA molecules that have extensive regions that are double-stranded and extensive regions that are single stranded. What are the main structural features of the tRNA molecule?

- A site for attaching an amino acid (the acceptor site) - An anticodon

What are the three parts of a nucleotide?

- At least one phosphate group - A pentose sugar - A nitrogenous base

Under some conditions, B DNA can be converted to Z DNA. Which conditions promote the formation of Z DNA from B DNA?

- Base methylation under low ionic conditions - Alternating purines and pyrimidines in high ionic condtions

How can nucleotides found in DNA be discriminated from those found in RNA? - DNA nucleotides never contain uracil - DNA nucleotides lack a 3' hydroxyl group - DNA nucleotides contain ribose - DNA nucleotides contain deoxyribose - DNA nucleotides are never pyrimidines - DNA nucleotides may contain thymine

- DNA nucleotides never contain uracil - DNA nucleotides contain deoxyribose - DNA nucleotides may contain thymine

RNA molecules can contain both single-stranded and double-stranded regions. In an RNA molecule with both single and double stranded regions, what is the orientation of the bases in the single and double stranded parts of the molecule?

- Double stranded region; bases project towards center of helix - Single stranded region; bases project outwards

What are the main structural features of an RNA double-helix?

- Helix has a right-handed twist - Strands of RNA are antiparallel - Turns of the helix consist of 11-12 base pairs

RNA molecules are, on average, much shorter than chromosomal DNA. Approximately, what is the size range of most RNA molecules?

A few hundred to several thousand nucleotides long

What is a nucleotide?

A nucleoside with an attached phosphate group

Under certain in vitro conditions, triplex DNA can form. What is triplex DNA?

A triple-helical DNA structure

DNA sequences with a high proportion of base-pairs between __ and __ are most stable.

G; C

Who discovered the structure of the DNA double helix?

James Watson & Francis Crick

What does it mean for two strands of DNA to be complementary?

The bases of one strand can base-pair with the bases of the other strand

B DNA can be converted to the Z DNA conformation under certain conditions. In what cellular process is Z DNA believed to have a role?

Transcription

T/F: Crick and Watson had to assume that the nucleotides in DNA were all linked together in chains, and using the same kind of bond.

True

What does a phosphodiester bond link together?

Two sugars on adjacent nucleotides in DNA or RNA

Two types of sturctures DNA can form

Z DNA and B DNA

Chargaff's rule states that, "in a piece of double-stranded DNA, the amount of ____ equals the amount of thymine and the amount of cytosine equals the amount of ____.

adenine; guanine

When two strands of DNA in a double helix run in opposite directions, one 5' to 3' and the other 3' to 5', what is this called?

antiparallel

In a nucleotide, the 1' carbon of the sugar is attached to the ____, the 5' carbon is attached to the ______, and the 3' carbon is attached to a ______.

base; phosphate group; hydroxyl

When comparing purines with pyrimidines, the best way to tell the difference between them is to look at the ring structures of the nitrogenous _____.

bases

Some proteins can interact with the major groove in the surface of a DNA double helix. These proteins recognize specific sequences of ____ in the groove, and interact with the groove via the formation of ______ bonds; thus the protein interacts very specifically with a particular region of DNA.

bases; hydrogen

Imagine you looked along the central axis of a right-handed DNA double-helix so that the spirals twisted away from you. In what direction would the spirals twist as you looked along the axis of the molecule.

clockwise

A nucleoside composed of the base cytosine attached to ribose is called

cytidine

A nucleoside that is composed of the base adenine attached to a deoxyribose is called

deoxyadenosine

In a DNA double helix, the bases point towards the ___ of the helix.

inside

Due to the twisting of the two strands of DNA around each other in a DNA double helix, grooves form on the surface of the molecule. What are the names of these grooves?

major and minor grooves

To help them understand the data that Rosalind Franklin obtained by X-ray diffraction studies, Crick and Watson used molecular ____ to develop representations of the DNA double-helix.

models

A sugar, such as ribose or deoxyribose, attached to a base but not to a phosphate group is called a ______.

nucleoside

DNA is negatively charged because of the negative charge found on the ____ groups in the DNA backbone

phosphate

Triplex DNA can form under certain conditions and although it remains unclear, it is possible that triplex DNA plays a role in _____.

recombination

The nucleotides use to make RNA and DNA are made from three main parts. One of those parts is a sugar molecule; in RNA the sugar molecule is called

ribose

The conventional direction of the spiral in the DNA double helix is ____ handed.

right

The structure of DNA that Crick and Watson proposed has _____ (number) strands of DNA that are wrapped around each other to form a double helix. The DNA bases of each strand of DNA point towards the central axis of the molecule and are held together by ____ bonds.

two; hydrogen

What was the main technological advancement that contributed to Crick and Watson working work out the structure of the DNA double-helix?

x-ray diffraction

Which descriptions from the list are the four fundamental levels of complexity seen in DNA? - Nucleotides are the building blocks of nucleic acids - The double helix associates with the plasma membrane to form looped structures - Two strands of DNA can associate to form a double helix - The double helix can bend and wrap to form complex structures - Lipids and carbohydrates associate with the double helix to form tertiary structures - Nucleotides are linked together to form nucleic acids

- Nucleotides are the building blocks of nucleic acids - Two strands of DNA can associate to form a double helix - The double helix can bend and wrap to form complex structures - Nucleotides are linked together to form nucleic acids

Which two main structural features result in complementary sequences of DNA forming a double helix? - The length of the phosphodiester bonds between nucleotides - The bases stack on top of one another - Hydrogen bonding between the bases - The use of deoxyribose versus ribose in DNA nucleotides - The absence of uracil in DNA nucleotides

- The bases stack on top of one another - Hydrogen bonding between the bases

Main structural features of DNA found in the Z conformation

- There are 12 base-pairs perturn - The helix is left-handed - The bases are tilted relative to the central axis of the molecule - The sugar-phosphate backbone zig-zags slightly

The X-ray diffraction data collected by Rosalind Franklin predicted that the DNA double helix contains __ base-pairs per complete turn of the helix.

10

When was the structure of the DNA double-helix discovered?

1953

When adenine base pairs with thymine, ___ hydrogen bonds form, and when cytosine base pairs with guanine, ___ hydrogen bonds form.

2;3

If one strand of DNA has the sequence 5'ATGCTACATA3', what would be the sequence of the bases on the complementary strand of DNA?

3'TACGATGTAT5'

A single turn of the DNA double-helix has a length of ____ nm.

3.4

Most abundant conformation seen in living cells?

B DNA

Molecular genetics studies the structure of

DNA

The two types of nucleic acid are known as ___ and ____.

DNA; RNA

What kind of sugar is found in DNA?

Deoxyribose

What are the features of the structure that forms when short regions of RNA form base-pairs?

Double-stranded and helical

dCTP

Nucleotide found in DNA with three phosphate groups

Guanosine triphosphate

Nucleotide used to make RNA that contains three phosphate groups

UMP

Nucleotide with ribose sugar and a single phosphate group

ADP

Nucleotide with ribose sugar with two phosphate groups

In a DNA double helix, where is the sugar phosphate-backbone located?

On the outside of the helix

The AT/GC base-pairing rule requires that the purines (A and G) always base-pair with the pyrimidines (T and C). Why is this?

Pairing a purine with a pyrimidine ensures a consistent diameter of the helix.

The data upon which Crick and Watson based their model of the DNA double-helix were from x-ray diffraction patterns from wet DNA fibers. These data were collected by the scientist

Rosalind Franklin

What is the fundamental repeating structural unit of DNA and RNA?

The nucleotide