Chapter 9: DNA & its role in heredity

Question 1

DNA is semiconservative. What does this mean?

Answer 1

Each double helix in the new generation retains one original copy strand and one new copy wrapped around each other.

Question 2

Long after Mendel’s work, many scientists contributed to DNA as _(1)

Answer 2

(1) being the carrier of genetic info

Question 3

What did Erwin Chargaff do?

Answer 3

Deciphered relative amounts of different nucleotides

Question 4

What did Rosalind Franklin do?

Answer 4

Showed that DNA is some sort of helix

Question 5

What did James Watson and Francis Crick do?

Answer 5

Put Chargaff and Franklins findings all together to determine overall structure of DNA

Question 6

What is Chargaff’s Rule?

Answer 6

In DNA there are equal amounts of adenine and thymine, and equal amounts os guanine and cytosine.The number of pyramidines and purines is the same

Question 7

How many rings does a pyramidine and purine have? Which bases are pyramidine/purines?

Answer 7

Pyramidines have one ring
- Thymine, cytosine, uracil

Purines have 2 rings
- Adenine, guanine

Question 8

What are the three things that DNA is made of?

Answer 8

A base, sugar, and phosphate group

Question 9

The amount of A + T and G + C in an organism is used to classify _____(1)

Answer 9

(1) bacteria

Question 10

The 3D structure of DNA was determined by the method of ___(1). by ___(2)

Answer 10

(1) X-ray crystallography
(2) Rosalind Franklin

Question 11

What are the three key features of DNA STRUCTURE, as defined by Watson and Crick?

Answer 11

1. DNA is a double stranded helix of uniform diameter
2. DNA runs antiparllel
3. The outer edges of the nitrogenous bases are exposed in the major and minor groove.

Question 12

The major and minor grooves serve as ___(1). The bases can form ____(2) in addition to the hydrogen bonds they form with complementary bases in the other strand.

Answer 12

(1) binding sites for proteins, the major groove has more space so proteins tend to bind there more
(2) non-covalent interactions with proteins

Question 13

How do we identify major and minor grooves?

Answer 13

Major and minor grooves alternate.

Draw triangles in the spaces and whichever triangle is bigger will be the major groove

Question 14

Binding of proteins to _______(1) is very important for DNA-protein interactions, such as those involved in ___(2)

Answer 14

(1) specific base pair sequences

(2) DNA replication and gene expression

Question 15

What are 4 biological features of DNA?

Answer 15

1. It stores all of an organism’s genetic info
2. It is susceptible to mutation
3. It must be precisely replicated in the cell division cycle
4. It is expressed as the phenotype

Question 16

What 3 things did Arthur Kornberg discover are needed to make DNA?

Answer 16

• dATP, dCTP, dTTP, dGTP
• DNA polymerase(enzyme)
• DNA to act as a template

Question 17

In DNA replication, one strand is copied ___(1), while the other strand must be copied ____(2).

Answer 17

(1)continuously (leading strand)
(2) backwards in short loops (lagging strand)

Question 18

Which enzyme unwinds DNA?

Answer 18

helicase

Question 19

At each origin of replication, DNA synthesis proceeds __(1). This means that replication offers move in ___(2).

Answer 19

(1) bidirectionally
(2) opposite directions

Question 20

Which direction are free nucleotides added to a growing DNA strand?

Answer 20

Free nucleotides are added to the 3’ end

DNA grows in the 5 –> 3 direction

Question 21

Which two scientists showed that DNA is semi-conservative?

Answer 21

Matthew Meselsin and Franklin Stahl

Question 22

As DNA unzips ___(1) replication bubble and ___(2) replication forks are formed. Each replication fork moves __(3) from the origin of replication(ori)

Answer 22

(1) one
(2) two
(2) away

Question 23

Due to the antiparallel arrangement of template strands, new daughter strands are extended in ___(1) at each fork

Answer 23

opposite directions

Question 24

The strand that grows in the same direction as the replication fork and is extended continuously is called the ___(1). The strand that grows away from the replication form is extended discontinuously in smaller fragments, called ____(2), is know as the ___(3).

Answer 24

(1) leading strand
(2) Okazaki fragments
(3) lagging strand

Question 25

DNA polymerases can make mistakes in replication but most errors are repaired. How does this work? What about mistakes that are not corrected?

Answer 25

As DNA polymerase adds nucleotides, it has a proofreading function and if bases are paired incorrectly, the nucleotide is removed.

Mistakes that are not corrected are mutations

Question 26

What are some practical applications of DNA replicaiton

Answer 26

PCR
- DNA fingerprinting
- Genetic diagnosis
- Food safety
- Biology research

DNA sequencing
- Genetic diagnosis
- Biology research

Question 27

What happens to the ends of eukaryotic chromosomes during DNA replication? Why does this happen? How do cells fix this problem.

Answer 27

This is called the “End Replication Problem”

Telomeres on the 4 ends of chromosomes shorten over time as a normal consequence of aging.

How does this problem arise: The leading strand is extended all the way to the end of the chromosome. However the lagging strand is unable to keep up and after the RNA primer is removed in the 3’ end, there is an overhand.

Some cells fix the end replication problem using telomerase. Some cells that keep dividing have telomerase, which extends telomere, and keeps the telomere of the chromosomes from shortening. Some examples of cells that have telomerase are bone marrow, gamete cells,a dn cancer cells.

Telomerase does not solve the end replication problem in ALL cells

Question 28

Replication forks always move ___(1) from the origin of replication

Answer 28

(1) away

Question 29

telomerase is an enzyme made of __(1).

Answer 29

(1) protein and RNA

Question 30

The ___(1) portion of telomerase eventually acts as a ___(2) for DNA polymerase to fill in the missing part of the original lagging strand.

Answer 30

(1) RNA
(2) Template

Question 31

How does DNA replication work?

Answer 31

1. Begins at a sequence of nucleotides called the origin of replication.
2. Helices unwinds the double stranded DNA helix
3. Single strand binding proteins react with eh single stranded regions of the DNA and stabilize it
4. DNA polymerase III adds nucleotides to the 3’ end of a pre existing chain of nucleotides ad it can not initiate a nucleotide chain. Therefore, an RNA polymerase, called a primase, constructs an RNA primer, which is a sequence of 10 nucleotides complementary tot he parent DNA. Primase is needed for the leading and lagging strand.
5. DNA Polymerase II can then add DNA to synthesize the new complementary strand of DNA.

For the lagging strand:
- synthesized discontinuously as a series of short Okazaki fragments
- When the DNA polymerase III reaches the RNA primer on the lagging strand, it is replaced by DNA polyermease I, which remove the RNA and replaces it with DNA
- DNA ligase then attaches and forms phsophodiester bonds. It joins all the fragments
- The DNA is further wound, primers are added, and the process repeats.

Question 32

There is no coding strand in ____(1). Everything is a template strand.

Answer 32

(1) DNA replication

Question 33

How does DNA polymerase II know when to stop replicating?

Answer 33

it ends at the end of the linear chromosome or when it reaches the ori in a circular DNA

Question 34

Is everything the same between prokaryotes and eukaryotes in DNA replication?

Answer 34

Yes