Molecular biology

Question 1

what are the steps of attachment of aa to tRNA

Answer 1

Recognition of tRNA
2. Activation of the amino acid
3. Charging of tRNA (RAC)

Question 2

which enzyme attaches aa to tRNA

Answer 2

amino acyl-tRNA synthetase

Question 3

describe the structure of tRNA

Answer 3

tRNA is described as clover-shaped with
anticodon at one end which interacts with
the mRNA and the acceptor end which
interacts with its particular aa

Question 4

what is the name and position of the two sequences conserved in the promoter

Answer 4

The first is about 10 nt before the transcription start
site (-10) called the pribnow box with the consensus
sequence TATAAT.
* The second site is about 35 nt before that transcription
start site (-35) with the consensus sequence TTGACA.

Question 5

what is a promoter

Answer 5

The site on the DNA where the RNA
polymerase binds and initiate RNA synthesis is
called a promoter

Question 6

types of transcription terminators

Answer 6

Inverted repeats
❖GC rich region followed by AT rich
region
❖In E.coli a protein called Rho.

Question 7

what is the purpose of tRNA

Answer 7

RNA is responsible for binding the
correct aa and bringing it to the growing
polypeptide chain during protein
synthesis.

Question 8

what are the 4 steps of protein synthesis?

Answer 8

Initiation
2. Elongation
3. Termination/release
4. Peptide folding

Question 9

what are the components of the initiation complexInitiation
2. Elongation
3. Termination/release
4. Peptide folding

Answer 9

30S ribosome subunit
mRNA
N formylmethionine tRNA
Initiation factors
* The 50S ribosome subunit is added to the initiation
complex.
* Preceding the initiation complex is the ShineDelgarno sequence on the mRNA where it binds to
the ribosome

Question 10

funtion of shine delgarno sequence

Answer 10

initiates protein synthesis by aligning the ribosome with the start codon

Question 11

what are molecular chaperones

Answer 11

The native protein is folded into its active
form by proteins called molecular
chaperones

Question 12

explain one method of post translation regulation of enzymes

Answer 12

A major mechanism of controlling enzyme
activity is by feedback inhibition.
* This occurs when the product of the enzymatic
activity inhibits the enzyme. (fi [wi] pie)
* This occurs because of the allosteric property of
the enzyme.

Question 13

what is an allosteric enzyme

Answer 13

An allosteric enzyme has 2 important binding
site:
– Active site where the substrate binds
– Allosteric site where the inhibitor (effector)
binds.
* When the inhibitor binds it causes
conformational changes in the active site and
prevents the substrate from binding

Question 14

explain transcriptional control

Answer 14

For transcription to take place RNA polymerase
must bind to the promoter of the DNA and
synthesize mRNA.
* Transcriptional control usually involves a
protein that binds to the DNA and increases or
decreases transcription
Enzymes involved in the synthesis of a specific
product are not synthesized if the product is
present.
* Enzymes involved in the synthesis of arginine
are only synthesized if arginine is absent.
* If arginine is present it will suppress the
enzymes.

Question 15

Lactose induces the production of which enzyme?

Answer 15

Beta galactosidase

Question 16

Arginine is the co-repressor for which enzymes?

Question 17

what method does bacteria use to regulate metabolism iin response to environmental changes

Answer 17

signal transduction

Question 18

what does the two component system for signal transduction consist of and name their functions?

Answer 18

Sensor protein in the cell membrane which
is usually a sensory kinase (enzyme which
phosphorylates)
☻Response regulator in the cytoplasm.
* The sensory kinase detect a signal in the
environment and phosphorylates itself at a
specific histidine residue

Question 19

example of two component systems

Answer 19

Nitrogen fixation in Rhizobium
Ω Sporulation in Bacillus

Question 20

what is the purpose of restriction enzymes and how are they used in DNA recombitant technology

Answer 20

Restriction enzymes (restriction
endonucleases) recognize specific
sequences in DNA and cleaves the DNA
at these specific sequences.
This makes it possible for molecular
biologists to isolate, modify and move
genes from one organism or place in an
organism to another.

Question 21

name the restriction enzymes of the folowing
bacillus subtilis
Escherichia coli

Answer 21

BsuR1
EcoR1

Question 22

Name one process in which DNA can be separated

Answer 22

agarose gel electrophoresis
DNA is digested with restriction enzyme and the resulting fragments are separated based on their sizes and charges in gel electrphoresis

Question 23

what are the steps in DNA cloning

Answer 23

Isolation of the desired DNA (gene).
* The DNA and the vector (plasmid) are digested
with the same restriction enzyme
* Joining of the DNA into the cloning vector using
DNA ligase (enzyme) to form a recombinant
DNA. (DNA ligase as there is also RNA ligase)
* Introduction of this recombinant DNA into
the desired host (transgenic organism)

Question 24

Name and describe the two methods of DNA sequencing

Answer 24

The Maxim Gilbert method uses chemicals that
break the DNA at the four nucleotides.
* The Sanger method actually makes copies of the
DNA to be sequenced but uses a special
molecule (dideoxynucleotide) which causes
termination of the sequences if it is incorporated
into the DNA

Question 25

Draw the structure of dideoxyribonucleoside trisphosphate

Question 26

what is nucleic acid hybridization and which property of DNA allos it to work

Answer 26

Nucleic acid hybridization: makes it
possible to find a specific sequence of
DNA or RNA in a large population of
nucleic acids.
* When DNA is denatured it becomes single
stranded (ssDNA) and it will form a hybrid
with another complementary ssDNA (probe).
* This property of DNA is taken advantage of in
DNA hybridization