W8

Question 1

What is a nucleotide?

Answer 1

A monomer of DNA that consists of a sugar, a base and a phosphate group

Question 2

What is the sugar in DNA technically?

Answer 2

2’ deoxyribose because the chemical group projecting downwards from the 2’ carbon is H-

Question 3

Why is the phosphate group that is attached to the 5’ carbon have a negative charge?

Answer 3

Becuase of free hydroxyl groups attached to the phosphorus atom are ionized by the loss of a proton.

Question 4

True or false DNA is a mild acid

Answer 4

True

Question 5

Where us the base attached on the sugar?

Answer 5

1’ carbon

Question 6

What is the name of he bond which connects one nucleotide to the next, and what type of bond is it?

Answer 6

Phosphodiester bond, which is a covalent bond (connects C-O-P-O-C)

Question 7

What characteristic does the phosphodiester bonds give the DNA?

Answer 7

Polarity

Question 8

What indicates whether the end is 5’ or 3’?

Answer 8

5’ has a free phosphate head and 3’ has a hydroxyl

Question 9

How many base pairs are there per turn?

Answer 9

10

Question 10

What is the diameter of a DNA molecule?

Answer 10

2nm

Question 11

What are the major and minor grooves?

Answer 11

The outside contours of the twisted strands

Question 12

What is the purpose of major and minor grooves?

Answer 12

Allow proteins that interact with DNA to make contact with bases via the grooves

Question 13

What does anti-parallel mean?

Answer 13

The DNA strands run in opposite direction 1.5’-3’ 2.3’-5’

Question 14

What are the two structures that a base could be?

Answer 14

Purine or a pyrimidine.

Question 15

Why are bases paired as a purine and pyrimidine?

Answer 15

To preserve the distance between the backbones. two purines= too bulged and 2 pyrimidines= too narrow

Question 16

What is the reason for the specificity with base pairing?

Answer 16

A+T= 2 hydrogen bonds formed
G+C=3 hydrogen bonds formed.
A hydrogen bond is formed when an electronegative O or N fro one base shared a hydrogen atom with another electronegative atom in the base

Question 17

What is base stacking?

Answer 17

It is a stabalizing force that occurs because the non-polar, flat surfaces of the bases tend to group together away from water molecules, hence tightly stacking together

Question 18

What is it in the structure of DNA which suggests that genetic information is encoded in the base sequence?

Answer 18

The lack of sequence in the bases

Question 19

What is the base-pairing rule?

Answer 19

%A+%T=%C+%G

%R=%Y

Question 20

How is DNA packaged in prokaryotic cells?

Answer 20

The circular DNA forms supercoils in which the circular molecules coils upon itself

Question 21

What causes supercoiling?

Answer 21

Enzymes called toposomerases which cleave ,partially unwind, and reattach a DNA strand, puuring strain on the DNA. Supercoils relieve the strain

Question 22

How is DNA packaged in eukaryotes?

Answer 22

Packaged with proteins known as histones and others to form a chromatin

Question 23

Why are histones found in all eukayotes?

Answer 23

Because they are evolutionary conserved, therefor they have a similar sequence from one organism to the next

Question 24

What is RNA?

Answer 24

A polymer of nucleotdes linked by phosphodiester bonds similar to those in DNA

Question 25

What are the main differences between DNA and RNA?

Answer 25

• Sugar in RNA is ribose and carries a hydroxyl group on 2’ carbon
• U replaces T
• 5’ end of DNA is typically mono-phosphate the 5’ end of RNA is usually triphosphate
• RNA is usually shorter
• RNA is single stranded

Question 26

What is a quick summary of transcription?

Answer 26

A region of the DNA duplex unwinds, one strand is used as a template for the sythess of RNA transcript that is complimentary to the DNA strand.
The transcript is produced by polymerization of ribonucleoside triphosphates

Question 27

What is the enzyme that carries out the polymerisation of RNA and which direction does it work?

Answer 27

RNA polymerase. It acts by adding successive nucleotides to the 3’ end of the growing transcript

Question 28

What direction are nucleic acids synthesized?

Answer 28

They are synthesized by the addition of nucleotides to the 3’ end. They grow in a 5’-3’ direction, the 3; direction

Question 29

What is the promoter region?

Answer 29

Regions that contain typically a few hundred base pairs where RNA polymerase and associated proteins can bind to the DNA duplex

Question 30

What is the common promoter region in eukaryotes

Answer 30

5’-TATAAA-3’ TATA box

Question 31

What are housekeeping genes?

Answer 31

Genes which products are needed at all times in cells.

Question 32

What is a sigma factor?

Answer 32

A protein that mediates the recognition of the promoter in bacteria . Facilitates the binding of NA polymerase

Question 33

What are transcription factors?

Answer 33

A set of proteins that bind to the promoter of a gene whose combined action is necessary for transcription

Question 34

What are transcriptional activator proteins?

Answer 34

A protein that binds to a sequence in DNA to enable transcription to begin. Help control when and in which cells transcription of a gene will occur

Question 35

What is a mediator complex?

Answer 35

A complex of proteins that interacts with the Pol II complex and allows transcription to begin. Recruited after transcriptional activator proteins have bound to enhancer DNA sequences

Question 36

What is the RNA polymerase complex responsible for transcription of protein-coding genes in eukaryotes?

Answer 36

Pol II