Lecture 11 DA

Question 1

To which carbon does the phosphate group attach to in nucleic acids? Where will the next nucleotide join to, and what group is found here?

Answer 1

5’ carbon.

Next nucleotide joins to the 3’ hydroxyl.

Question 2

What is found at the 2’ carbon in DNA vs RNA?

Answer 2

DNA - H

RNA - OH

Question 3

What bases are purines, and how many rings do they have? What about the pyrimidine bases?

Answer 3

Purines
A, G - are double ringed
Pyrimidines
C, U, T - are single ringed

Question 4

If a base has a sugar attached, what is the naming convention?

Answer 4

-sine suffix is added.

Question 5

How can genes be inactivated?

Answer 5

Methylation.

Question 6

What is the link between nucleotides?

Answer 6

Phosphodiester bond.

Question 7

What wavelength do nucleotides absorb highly at, and why?

Answer 7

At 260nm, due to their ring structure.

Question 8

How long is an AT bond? What about GC? How many pairs of H bond each?

Answer 8

AT - 11.1A long, 2 H bonds

GC - 10.8A long, 3 H bonds

Question 9

Which is stronger, AT or GC bonds?

Answer 9

GC

Question 10

How much space is between each nucleotide?

Answer 10

Bases are spaced out 3.4A apart.

Question 11

How wide is DNA?

Answer 11

10A

Question 12

What are the minor and major grooves?

Answer 12

Minor grooves are where the DNA pairs bind, between them are the major grooves.

Question 13

How long is one turn of the DNA?

Answer 13

36A.

Question 14

What direction does DNA synthesis occur?

Answer 14

5’ to 3’.

Question 15

In DNA synthesis/replication, are both strands synthesised continuously?

Answer 15

No, the 3’ to 5’ direction is synthesised in pieces at a time known as okazaki fragments and later ligated by DNA ligase.

Question 16

Name the three forms of DNA. Which is the most common, and are they left handed or right handed?

Answer 16

A form - right handed, like the B form, but shorter and thicker.
B form - right handed, most common.
Z form - left handed, very unstable.

Question 17

What is the base pair sequence of Z form DNA?

Answer 17

Alternating purines and pyrimidines.

Question 18

What is a palindrome in nucleic acids? What about mirror images?

Answer 18

Palindrome sequences repeat on the other strand.

Mirror images repeat on the same strand.

Question 19

What structures can palindromes and mirror images form? Is it spontaneous?

Answer 19

Hairpins, cruciforms, bulges and internal loops. Requires energy.

Question 20

What is the rate of annealing determined by?

Answer 20

The GC content, higher GC means it will melt more quickly.

Question 21

What is the melting temperature for DNA?

Answer 21

The point where half the DNA is melted.

Question 22

What can UV light on DNA induce (which bases specifically)? What is a consequence of this?

Answer 22

Can induce pyrimidine dimers. Makes a kink in the DNA, causing mutation.

Question 23

What is a common source of DNA mutation?

Answer 23

Methylation.

Question 24

What does mitochondrial DNA encode? Is it enough for what the mitochondria needs?

Answer 24

DNA replication, transcription, translation, but not anything the mitochondria needs, such as proteins etc. Mitochondria’s needs come from the cytosol.

Question 25

What are genes composed of (3)?

Answer 25

Start codon, reading frame, stop codon.

Question 26

What sequences in genes contribute, and dont contribute to proteins?

Answer 26

Introns dont contribute, exons do.

Question 27

What percentage of the genome do exons make up?

Answer 27

1.5%

Question 28

What are the ends of DNA called, and what is its typical sequence in humans?

Answer 28

Telomeres, and shorten over time. TTAGGG repeats can be found in human telomeres.

Question 29

What are telomeres like in cancer?

Answer 29

Well taken care of.

Question 30

What is a chormatin?

Answer 30

When DNA wraps around a histone protein.

Question 31

Name the order of DNA coiling beginning with chromatin (6)?

Answer 31

Chormatin wraps around to form a fibre.
Fibres loop around once to form a loop.
6 loops form a giant loop to form a rosette.
30 rosettes form a giant loop to form one coil.
10 coils form 1 chromatid.
2 chromatids per chromosome.

Question 32

Where do two chromatids join to form a chromosome?

Answer 32

Centromere.

Question 33

What enzyme carries out transcription? How many bases are unwound by it at any given time?

Answer 33

RNA polymerase. Unwinds 17 bases at any given time. RNA is formed from it, then rewound.

Question 34

In RNA transcription, is the coding strand the template strand?

Answer 34

No, it is the non-template strand.

Question 35

What is an easy way to convert the template strand to the RNA transcript?

Answer 35

Change all the Ts to a U.

Question 36

What is the promoter sequence?

Answer 36

Recruits the polymerase.

Question 37

What do all reading frames begin with, and what does it code for?

Answer 37

AUG, coding for methionine.

Question 38

What are the three stop codons?

Answer 38

UAA
UAG
UGA

Question 39

What is meant by the degeneracy of the genetic code? What is its purpose?

Answer 39

More than one codon per amino acid. 20 amino acids, but 64 possibilities.
Allows for redundancies, and allows different organisms to use different codons according to what resources are available.

Question 40

Are codons always specific to one amino acid? Is this universal in all organisms?

Answer 40

No, there are exceptions where codons can code for a different amino acid, not always consistent.

Question 41

What is the anticodon?

Answer 41

Codon found on the tRNA.

Question 42

What is the tRNA wobble?

Answer 42

The first and second bases on the anticodon bind well, but the third can wobble, but doesnt affect efficiency of tRNA.

Question 43

What sequence does the ribosome bind to? Where is it found (2)?

Answer 43

Shine-delgano sequence. Found upstream of the start codon, also found in 16S RNA for complimentarity.