CH.6 Nucleic acids and protein synthesis

Question 1

what is a nucleotide?

Answer 1

a molecule consisting of a nitrogen-containing base, a pentose sugar and a phosphate group.
phosphodiester bonds join nucleotides to form a chain called polynucleotide

Question 2

Name the base pairings in DNA

Answer 2

Adenine- Thymine
Guanine- Cytosine

Question 3

Name the base pairings in RNA

Answer 3

Adenine- Uracil
Guanine- Cytosine

Question 4

phosphodiester bond

Answer 4

a bond joining two nucleotides together; there are two ester bonds, one from the shared phosphate group to each of the sugars either side of it

Question 5

Features of DNA

Answer 5

two polynucleotide chains
each chain is a right-handed helix
double helix
antiparallel chain
sugar-phosphate backbone with bases projecting at right angles
each base is attracted to the other by hydrogen bonds. This holds the chain together
complementary base pairing
2 hydrogen bonds between A-T and 3 for G-C
adenine and guanine are purines; thymine, uracil and cytosine are pyrimidines
complete turn every 10 base pairs

Question 6

What is complementary base pairing?

Answer 6

the hydrogen bonding of A with T and of C with G in nucleic acids

Question 7

Differences in hydrogen bonding between A-T and G-C

Answer 7

A-T 2 hydrogen bonds
G-C 3 hydrogen bonds

Question 8

How many rings do purines and pyrimidines have?

Answer 8

purines two rings
pyrimidines three rings
distance between purine and pyrimidine is three rings ( always constant)

Question 9

What is semi-conservative replication?

Answer 9

the method
by which a DNA molecule is copied to form
two identical molecules, each containing one
a strand from the original molecule and one newly
synthesised strand

Question 10

Describe the semi-conservative replication of DNA and in what phase of the cell cycle does it occur in

Answer 10

S phase of cell cycle
Unwinding Process:

The two DNA strands separate through a process called ‘unzipping’ by using the enzyme Helicase.
Hydrogen bonds holding the strands together are broken.

Enzyme DNA polymerase is used for the copying process.
Attaches to single strands and adds new nucleotides one at a time.
Copying Direction Challenge:
DNA polymerase can only copy in the 5′ to 3′ direction.
Leading Strand: Copied in the same direction as unwinding.
Lagging Strand: Copied in the opposite direction, requiring backtracking.
Okazaki Fragments:

The lagging strand results in short fragments called Okazaki fragments.
Named after the biochemist who discovered them.

Question 11

DNA polymerase

Answer 11

an enzyme that copies DNA;
it runs along the separated DNA strands lining
up one complementary nucleotide at a time
ready for joining by DNA ligase
only copies in the 5’ to 3’ direction

Question 12

leading strand

Answer 12

during DNA replication, the
parent strand that runs in the 3′ to 5′ direction is
copied to produce the leading strand

Question 13

lagging strand

Answer 13

during DNA replication, the
parent strand that runs in the 5′ to 3′ direction is
copied to produce the lagging strand

Question 14

DNA ligase

Answer 14

an enzyme that catalyses the
joining together of two nucleotides with covalent
phosphodiester bonds during DNA replication

Question 15

What is a gene?

Answer 15

a length of DNA that codes for a particular polypeptide or protein

Question 16

Features of genetic code

Answer 16

triplet code
code is universal- each triplet codes for the same base in all living things
code has punctuations
code is redundant/ degenerate- some amino acids are coded by more than one triplet

Question 17

What is transcription?

Answer 17

copying the genetic information
in a molecule of DNA into a complementary
strand of mRNA; a single strand of the DNA is
used as a template (this is called the template or
transcribed strand) – the enzyme responsible is
RNA polymerase

Question 18

What is translation?

Answer 18

a stage in protein synthesis during
which a sequence of nucleotides in a molecule of
messenger RNA (mRNA) is converted (translated)
into a corresponding sequence of amino acids in
a polypeptide chain; it takes place at ribosomes

Question 19

What is a codon?

Answer 19

sequence of three bases on an mRNA
molecule that codes for a specific amino acid or
for a stop signal

Question 20

What is an anticodon?

Answer 20

the sequence of three unpaired bases
on a tRNA molecule that binds with a codon on
mRNA

Question 21

What is gene mutation?

Answer 21

a change in the base sequence
in part of a DNA molecule

Question 22

What is chromosome mutation?

Answer 22

a random and
unpredictable change in the structure or number
of chromosomes in a cell

Question 23

Types of mutation

Answer 23

• substitution – a base is replaced by a different base ( ex. Sickle cell anaemia)
• deletion – a base is lost and not replaced
• insertion – a base is added.

Question 24

What is frame-shift mutation?

Answer 24

a type of gene mutation
caused by insertion or deletion of one or more
nucleotides, resulting in incorrect reading of the
sequence of triplets in the genetic code due to a
shift in the reading frame