Protein Synthesis and Control

Question 1

Define anti-codon

Answer 1

A sequence of three adjacent nucleotides on a molecule of transfer RNA (tRNA) that is complimentary to a particular codon on a messenger RNA molecule

Question 2

Define codon

Answer 2

A sequence of three adjacent nucleotides in messenger RNA (mRNA) that codes for one amino acid.

Question 3

Define deletion mutation

Answer 3

A nucleotide is lost from the normal DNA sequence. This results in all the nucleotide after this point being read in the incorrect order This is known as a Frame shift.

Question 4

Define DNA helicase

Answer 4

An enzymes that acts on a specific region of the DNA molecule to break the hydrogen bonds between the bases causing the two strands to separate and expose the nucleotide bases.

Question 5

Define DNA replication

Answer 5

The process when the double helix of a DNA molecule unwinds and each strand acts as a template on which a new strand is constructed.

Question 6

Describe messenger RNA

Answer 6

The RNA that transfers the DNA code from the nucleus through the nuclear pore to the cytoplasm. The code it contains is used by ribosomes to determine the order in which the amino acids should be bound to form a protein.

Question 7

Define mis-sense mutation

Answer 7

The base change results in in a different amino acid being coded for. The polypeptide produced will differ in a single amino acid. The consequence will depend on where the amino acid was.

Question 8

Define mutation

Answer 8

A change in the sequence of bases in DNA

Question 9

Define non-sense mutation

Answer 9

A base change that has resulted in the formation of a stop codon. The production of the polypeptide will be stopped prematurely leading to a non functional protein.

Question 10

Define nucleotides

Answer 10

Complex chemicals made up of an organic base, a sugar and a phosphate. They are the basic units of DNA and RNA.

Question 11

Define RNA polymerase

Answer 11

Enzyme that joins together nucleotides to form messenger RNA during transcription.

Question 12

Define silent mutation

Answer 12

A substituted base that still codes for the same amino acid. There is no effect on the order of amino acids so no alteration of the polypeptide formed.

Question 13

Define transcription

Answer 13

Formation of messenger RNA molecules from the DNA that makes up a particular gene. This is the first stage of protein synthesis

Question 14

Describe transfer RNA

Answer 14

A small singe stranded chain of RNA folded into a clover leaf shape with one end of the chain extending beyond the other. Each molecule carries a single amino acid whose codon binds to its Anticodon.

Question 15

Describe translation

Answer 15

When mRNA is used as a template by ribosomes to which complementary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide chain.

Question 16

Define double helix

Answer 16

DNA nucleotides join together between the phosphate group and the sugar creating a sugar phosphate backbone. 2 DNA polynucleotides join by hydrogen bonding between the bases by complementary base pairing. 2 strands wind to form the double helix.

Question 17

Give the process of transcription

Answer 17

• DNA helicase breaks hydrogen bonds
• One strand used as a template for mRNA
• RNA polymerase adds complementary base pairs
• mRNA moves out of the nuclear pore and to the ribosome

Question 18

Give the process of translation

Answer 18

• tRNA carry amino acids to the ribosome
• tRNA with a complementary anticodon attaches itself to the mRNA
• The second tRNA attaches itself to the next codon in the same way
• the 2 amino acids join via peptide bonds
• the 1st tRNA leaves and so on until a stop codon is reached

Question 19

How do you control protein synthesis

Answer 19

By altering the rate of transcription of genes

Question 20

Define operon

Answer 20

A section of DNA controlling structural genes, control elements and a regulatory gene

Question 21

Define regulatory gene

Answer 21

A protein which binds to DNA and switches genes on or off by increasing or decreasing the rate of transcription

Question 22

What determines whether the transcription factor can bind to the DNA or not

Answer 22

The shape of a transcription factor

Question 23

What is the lac operon

Answer 23

an inducible protein

Question 24

What are the two substances e coli can respire

Answer 24

glucose

lactose

Question 25

Give 2 reasons the e coli doesn't always make the necessary enzymes for lactose respiration

Answer 25

 Making proteins that are not essential at that time will tie up resources such as amino acids  Uses a lot of energy unnecessarily

Question 26

What are the 2 lactose specific enzymes

Answer 26

Lactose Permease | Beta-Galactosidase

Question 27

What is the function of beta-galactosidase

Answer 27

Catalyses the hydrolysis of lactose into glucose and Galactose

Question 28

What is the function of lactose permease

Answer 28

Increases the cell’s permeability to lactose so it can take in more lactose from the surrounding environment

Question 29

What are the 5 regions on the lac operon

Answer 29

``` i p o z y ```

Question 30

What is the i region

Answer 30

Regulatory Gene which codes for a repressor protein

Question 31

What is the p region

Answer 31

p = Promoter region which | binds RNA Polymerase

Question 32

What is the o region

Answer 32

Operator region which | binds the repressor protein

Question 33

What is the z region

Answer 33

z = Structural gene for | Beta-Galactosidase

Question 34

What is the y region

Answer 34

y = Structural gene for lactose permease

Question 35

Describe what happens in a glucose rich environment/Lactose low environment

Answer 35

1. The regulatory gene undergoes transcription and translation and a repressor protein is synthesised 2. The repressor protein has 2 binding sites, one of which binds to lactose the other to the operator region. 3. In the absence of lactose the repressor protein binds to the operator region and blocks part of the promoter region of the lac operon. 4. This prevents RNA Polymerase binding to the promoter region 5. This therefore prevents transcription of the structural genes Z for BetaGalactosidase and Y for Lactose Permease.

Question 36

Describe what happens in a glucose low environment/Lactose rich environment

Answer 36

1. The regulatory gene undergoes transcription and translation and a repressor protein is synthesised 2. The repressor protein has 2 binding sites, one of which binds to lactose the other to the operator region. 3. In the presence of lactose the repressor protein binds to the lactose, which alters the shape of the repressor protein. 4. The repressor protein can now no longer bind to the operator region. 5. This leaves the promoter region free to bind RNA Polymerase 6. This therefore allows the transcription of the structural genes Z for BetaGalactosidase and Y for Lactose Permease. 7. Beta-Galactosidase catalyses the hydrolysis of lactose to glucose and galactose. 8. Lactose permease increases the cell’s permeability to lactose so it can take in more lactose from the surrounding environment

Question 37

What controls the development of body plan

Answer 37

Homeoetic genes

Question 38

Define homeobox genes

Answer 38

a type of gene which contains within its genetic code a | sequence of 180 bases, which is referred to as a Homeobox

Question 39

What are homeobox genes organised in

Answer 39

Hox clusters

Question 40

What does vitamin A activate

Answer 40

Homeotic genes in vertebrates

Question 41

Why should pregnant women avoid too much vitamin A

Answer 41

It can interfere with normal gene expression (particularly in fetus heads)

Question 42

Define apoptosis

Answer 42

Programmed cell death

Question 43

Give 2 molecules controlling apoptosis

Answer 43

Hormones Cytokines Growth factors Nitric Oxide

Question 44

Describe the process of apoptosis

Answer 44

1. Enzymes digest the cytoskeleton 2. Cytoplasm becomes dense as organelles become more tightly packed together 3. Blebs form (bulging) 4. Chromatin (DNA & proteins) condense and the nuclear envelope breaks 5. DNA fragments 6. The cell breaks apart forming apoptotic bodies (vesicle like structures) 7. These bodies package the harmful hydrolytic enzymes preventing damage to other cells 8. Phagocytosis of the cellular debris, some of which can be recycled.

Question 45

Define necrosis

Answer 45

premature cell death

Question 46

Give 2 causes of necrosis

Answer 46

o Infection o Trauma o Toxins

Question 47

What is the hayflicks limit

Answer 47

This refers to the believed number of mitotic divisions a cell can undergo before it is highlighted be destroyed and its components recycled. 50 divisions

Question 48

What disease is an example of when the hayflicks limit is not stuck to

Answer 48

Cancer (uncontrolled cell division)

Question 49

Define mutation

Answer 49

changes to the sequence of DNA nucleotides in a gene

Question 50

What cells do mutations occur in to affect the offspring

Answer 50

gametes

Question 51

What are the 3 levels that mutations can occur at

Answer 51

DNA Gene Chromosome

Question 52

Define genetic code

Answer 52

sequence of Nitrogenous bases (DNA) held in the gene

Question 53

How does cyclic AMP work

Answer 53

Activates proteins by altering their three-dimensional | structure