Molecular Genetics

Question 1

whats a nucleotide made of (3)

Answer 1

nitrogenous base
Pentose sugar
phosphate group

Question 2

What links nucleotide

Answer 2

Phosphodiester bond

Question 3

What makes up the sugar phosphate backbone

Answer 3

Alternating sugars and phosphate grps

Question 4

What does sugar phosphate backbone do

Answer 4

provides structural support to molecule

Question 5

What is joined to the base pairing to stabilize it

Answer 5

Hydrogen bonds

Question 6

Process of DNA replication

Answer 6

1. Both strands of a DNA molecule 
separate 
2. Both strands act as templates for the  synthesis of two new daughter 
strands. 
3. Formation of Phosphodiester bonds catalysed by DNA polymerase.
4. The sequence of DNA on the newly 
synthesised strands is determined by 
complementary base pairing.
5. Hydrogen bonds form between the 
bases of one old and one new strand 
to form a complete DNA molecule.
6. Each daughter cell inherits a DNA 
molecule that is a hybrid, consisting 
of one old and one new strand

Question 7

Where transcription happen

Answer 7

nucleus

Question 8

Where translation happen

Answer 8

cytoplasm

Question 9

Transcription (5)

Answer 9

1. The enzyme RNA polymerase attaches 
to DNA and starts to unwind and 
separate the DNA double helix.
2. One DNA strand acts as template.
3. RNA nucleotides base-pair one by one 
with DNA bases on the template DNA 
strand via complementary base 
pairing. 

4. RNA polymerase connects RNA 
nucleotides into a polynucleotide chain
by catalyzing the formation of 
phosphodiester bonds (between RNA 
nucleotides).
5. As RNA polymerase moves along the 
DNA, it unwinds and exposes more of 
the template DNA strand for base pairing with RNA nucleotides

Question 10

start codon

Answer 10

AUG

Question 11

Stop codons

Answer 11

UAA UAG UGA

Question 12

Does stop and start codons code for amino acid

Answer 12

STatrt codon codes for amino acid

stop codon doesnt

Question 13

Define translation

Answer 13

Conversion from the nucleic acid language to the

protein language

Question 14

What do codons do

Answer 14

sequence of codons Determine type and sequence of amino acids in polypeptide chain

Question 15

What is the role of TrNA (1) and what must they do in order to achieve this main role (2)

Answer 15

match amino acids to the correct codons to form a
polypeptide

– attach to specific amino acid
– recognise the matching correct codon(s) in the mRNA

Question 16

What do the two ends of TRna do (2)

Answer 16

1) One end of 
tRNA molecule is 
attached to a 
specific amino acid
2) Another end of 
tRNA molecule has 
3 exposed RNA 
nucleotides 
forming an 
anticodon

Question 17

How does TRNA attach itself to SPECIFIC Amino Acids

Answer 17

The anticodons are
complementary to the codons on
mRNA

Question 18

What is a Ribosomal RNA made up of (2)

Answer 18

 The smaller unit binds mRNA.

 The larger unit has 2 tRNA sites.

Question 19

What does ribosomal RNA do

Answer 19

• Ribosomes coordinate the binding of 
tRNA to mRNA.
• Ribosomes also catalyse formation of 
peptide bonds between amino acids 
to form polypeptide.

Question 20

Translation (5)

Answer 20

• The anticodon on each tRNA complementary base-pairs with a codon on the
mRNA.
• mRNA and tRNA are held together by the ribosome.
• As translation proceeds, in the ribosome there is always
– one tRNA carrying a growing polypeptide chain
– another incoming tRNA carrying the next amino acid to be added
• The ribosome links the growing peptide chain to the new amino acid from the
incoming tRNA (peptide bond formed).
• When ribosome reaches the stop codon, translation stops.

Question 21

What does DNA cloning do

Answer 21

it produces

many identical copies of the target DNA for use

Question 22

Why are bacteria used as host cells to clone DNA/ genes?

(2)

Answer 22

• Bacteria have very short doubling time or high
rates of reproduction (via binary fission)
• Growing recombinant bacteria results in very
high numbers of bacteria with the target gene in
a very short period of time.

Question 23

how is recombinant plasmid form

Answer 23

Bacterial plasmids are joined to target DNA

Question 24

WHats a bacterial plasmid

Answer 24

small, double stranded DNA molecules

Question 25

Why do scientists join target DNA to bacterial plasmid instead of bacterial chromosome (4)

Answer 25

plasmid … • can easily incorporate foreign DNA • is readily taken up by bacteria • often contain genes coding for antibiotic resistance o Easy to identify bacteria that had taken up the recombinant plasmid from those that didn’t • can self-replicate and so is present in one or more copies in one bacterium → greater yield of target DNA

Question 26

How does recombinant plasmids increase the yield of target DNA for use

Answer 26

• Recombinant plasmid self-replicate to produce multiple copies in each bacterium. • When the bacterium divides, recombinant plasmid is also replicated and passed on to its descendants. • Rapid reproduction of bacteria AND self-replication of recombinant plasmid together produces large number of copies of the target DNA

Question 27

What must restriction sites be

Answer 27

Palindromic

Question 28

how are Restriction enzymes precise in digesting DNA

Answer 28

Restriction enzyme cut BOTH strands of the DNA double helix at specific points in the restriction site which is palindromic

Question 29

How do restriction enzymes cut/ cleave the DNA?

Answer 29

``` Restriction enzymes cleave the sugar -phosphate backbone of DNA by catalysing the breaking of the phosphodiester bonds. ```

Question 30

What happens when plasmid and gene are cut using same restriction enzyme

Answer 30

``` This will produce the same sticky ends that are complementary. the exposed nucleotides on sticky ends can undergo complementary base-pairing and hydrogen bonding. to form recombinant plasmid ```

Question 31

What is the use of DNA Ligase

Answer 31

DNA ligase is used to repair the sugar-phosphate backbone (catalysing the formation of phosphodiester bond) to form an unbroken recombinant plasmid with an intact sugar phosphate backbone.

Question 32

Is Complementary base pairing catalysed by dna ligase

Answer 32

no

Question 33

2 rules to choosing restriction enzyme to use for dna cloning

Answer 33

Rule #1: Both plasmid and target DNA must be cut with the same restriction enzyme to produce complementary sticky ends. HENCE, both must have the restriction site sequence of the chosen enzyme in their DNA sequence Exception: When using restriction enzymes that produce blunt ends Rule #2: The restriction site sequence of the chosen restriction enzyme must not be found within the target DNA’s sequence. (Restriction sites should be flanking left AND right of the target DNA.)

Question 34

transformation

Answer 34

Transformation is to make host bacteria (usually E. coli) take up the recombinant plasmid. This step is often not efficient. • Bacteria that took up the plasmid is termed transformed bacteria • To identify transformed bacteria, plasmids MUST have a selectable marker. This marker is usually an antibiotic resistance gene. • Bacteria that is successfully transformed will take up plasmid with antibiotic resistance gene.

Question 35

Selection

Answer 35

bacteria is grown on nutrient medium containing the antibiotic. This step is known as Selection. • Transformed bacteria will survive and divide to form colonies but non-transformed bacteria will be killed by the antibiotic.

Question 36

Whats MCS

Answer 36

Multiple Cloning Site (MCS) contains a few unique restriction sites only found here on the plasmid. Point of insertion for target DNA.

Question 37

``` Q: How to decide if a particular restriction enzyme “X” can be used to clone target gene “Y” into plasmid “Z”? ✓ Does enzyme “X” cut at the MCS of plasmid “Z”? Ans: ✓ Does enzyme “X” cut at sites flanking both ends of target gene? ✓ Does enzyme “X” cut within target gene? ✓ Does enzyme “X” produce sticky ends?+ ```

Answer 37

``` Q: How to decide if a particular restriction enzyme “X” can be used to clone target gene “Y” into plasmid “Z”? ✓ Does enzyme “X” cut at the MCS of plasmid “Z”? Ans: Must be YES ✓ Does enzyme “X” cut at sites flanking both ends of target gene? Ans: Must be YES ✓ Does enzyme “X” cut within target gene? Ans: Must be NO ✓ Does enzyme “X” produce sticky ends? Ans: Preferably yes ```

Question 38

How does a DNA complementary abse pairing help it fulfil its function

Answer 38

A DNA molecule is double stranded / made up by two polynucleotide chains that are held by complementary base pairing between A and T nucleotides as well as G and C nucleotides. How does it relate to function? Complementary base pairing allows DNA to replicate itself accurately for transfer of genetic information from generation to generation.

Question 39

What gene and chromosome and Relationship between gene and chromosome

Answer 39

A gene is a sequence of DNA nucleotides that codes for a specific polypeptide by specifying the order in which amino acids must be joined together. AND A chromosome is a long double-stranded DNA molecule that is highly coiled and folded. – 1m Each chromosome contains many genes. – 1m

Question 40

What is complementary base pairing for

Answer 40

· Complementary base pairing (adenine pairs with thymine; guanine pairs with cytosine) allows the accurate copying / conservation of the base sequence of DNA during DNA replication. – 1m How? · As DNA replication is semi-conservative, both strands of a DNA molecule act as template for complementary base pairing to form new strands. · The new strands formed are complementary to their template strands but also identical to the other template. 2 pts – 1m (Hence, the resultant two DNA molecules are identical to each other / have the same base sequence.)

Question 41

Describe how human insulin formed (7m)

Answer 41

1. The human insulin gene is obtained from the chromosome by cutting it with a restriction enzyme that produces sticky ends; 2. The plasmid vector is cut with the same restriction enzyme, producing complementary sticky ends; 3. The plasmids are mixed with the DNA fragments and complementary base-pairing between the sticky ends of the insulin gene and the plasmid DNA occurs; 4. DNA ligase is added to the mixture to join / splice the cut ends of the DNA to form a continuous / unbroken recombinant plasmid; 5. The recombinant plasmids are mixed with E.coli bacteria and plasmids enter the bacteria; 6. Transformed bacteria containing the recombinant plasmid is selected on growth medium containing antibiotics; 7. Only transformed bacteria will survive to transcribe and translate the insulin gene on the recombinant plasmid into human insulin protein.

Question 42

natural function of restriction enzyme

Answer 42

Its natural function is to hydrolyze/ digest/ cut viral DNA + to protect bacteria from invading viruses