Nucleic Acids

Question 1

Summary 1

Answer 1

• The DNA molecule exists to be a store of information. It encodes the
  blueprint for making all living organisms.
• The complete DNA sequence in an organism is called its genome.
• Some parts of DNA contain genes, which are sections of DNA that contain
  information required to make other molecules. Humans have around 20,000
  genes.
• RNA is transcribed from DNA and used a template for the synthesis of
  proteins.
• Proteins carry out thousands of functions inside a living organism –
  everything to do with the structure, activity and regulation of cells, tissues
  and organs.

Question 2

SUMMARY – 2 – BUILDING BLOCKS

Answer 2

The term “nucleic acids” includes the molecules deoxyribonucleic acid
(DNA) and ribonucleic acid (RNA).
 Nucleic acids are built from monomers called nucleotides.
 The 3 components of a nucleotide are:
 Sugar (monosaccharide)
 Nitrogenous base
 Phosphate group
 Note: a nucleoside has base and sugar but NO phosphate.

Question 3

SUMMARY - 3

Answer 3

Pyrimidines have a single ring structure (mnemonic: long name → smaller structure).
Purines have a double ring structure (mnemonic: short name → bigger structure).

Question 4

SUMMARY - 4

Answer 4

 Individual DNA (and RNA) strands are ALWAYS synthesised in a 5′ to
3′ direction.
 In all double stranded nucleic acids the stands are antiparallel (i.e. they
run in opposite directions).
 A always pairs with T; G always pairs with C

Question 5

Differences between DNA and RNA

Answer 5

DNA
The permanent store of
genetic information
contained in the
nucleus of the cell.
Deoxyribose.
Uses the bases A, C, G,
T.
Forms a double helix
from 2 complementary
strands
RNA
Transferring genetic
information from the
nucleus to the
cytoplasm. Also protein
synthesis.
Ribose.
Uses the bases A, C, G,
U.
Usually present as a
single-stranded
molecule

Question 6

DNA and RNA are polymers made of monomers called

Answer 6

Nucleotides

Question 7

Pyramidines

Answer 7

Cytosine Thymine

Question 8

Purines and pyrimidines are

Answer 8

heterocyclic hydrocarbons

Question 9

Nucleotides can have one,
two or three phosphate groups

Answer 9

mono/di/triphosphate

Question 10

Sugar + base =

Answer 10

Nucleoside

Question 11

Sugar + base + phosphate group

Answer 11

Nucleotide

Question 12

If the base is Adenine Adenosine triphosphate ATP
If the base is Guanine Guanosine triphosphate GTP

Answer 12

PURINE

Question 13

If the base is Cytosine Cytidine triphosphate CTP
If the base is Thymine Thymidine triphosphate TTP
If the base is Uracil Uridine triphosphate

Answer 13

PYRAMIDINE

Question 14

Secondary messengers

Answer 14

 cAMP (cyclic adenosine monophosphate) – secondary messengers
 cGMP (cyclic guanosine monophosphate) – secondary messengers
 The general term for nucleoside triphosphates with deoxyribose
sugar: dNTP

Question 15

Oligonucleotides

Answer 15

Short (~20 nucleotides long)
Examples:
* RNA molecules that function as
“primers” to begin the duplication of
DNA;
* RNA molecules that regulate the
expression of genes;
* Synthetic DNA molecules used for
amplifying and analysing other,
longer nucleotide sequences (PCR
primers).

Question 16

Polynucleotides

Answer 16

Long (these are called nucleic acids)
Examples:
* Include DNA and some RNA.
* Are the longest polymers in the living
world. (Some DNA molecules in plants
and animals contain hundreds of millions
of nucleotides)

Question 17

Double Stranded Helix

Answer 17

with a sugar–phosphate
backbone on the outside and base pairs lined up on the inside

Question 18

Held together by CBP

Answer 18

In DNA:
Thymine pairs with adenine (T-A)
(T and A are complementary bases)
Cytosine pairs with guanine (C-G)
(C and G are complementary bases)
Formation of hydrogen bonds between a purine and a pyrimidine.
2 hydrogen bonds between T and A.
3 hydrogen bonds between C and G.

Question 19

Chargaff’s Rules

Answer 19

Rule 1
There is a 1:1 ratio of purine bases to pyrimidine bases in double-
stranded DNA.
Amount of A = amount of T.
Amount of G = amount of C.
Rule 2
The relative amounts of A-T and C-G vary between different
species.
e.g. E. coli has a GC content of 51%; humans, 41%; yeast, 38%.

Question 20

Other than hydrogen bonds, what kind
of forces hold the two strands
together?

Answer 20

2- Hydrophobic interactions
3- Van der Waals interactions
These interactions are called the ‘base stacking interactions’

Question 21

Reversible Reaction

Answer 21

However, heat will ‘denaturate’ DNA.
But this is a reversible
reaction.
Cooling down will
‘renaturate’ DNA.