eLFH - Gene transcription and translation

Question 1

Transcription definition

Answer 1

Process by which sequences of deoxyribonucleic acid templates produce specific messenger ribonucleic acid (mRNA) sequences

Question 2

Translation definition

Answer 2

Process by which mRNA determines the final amino acid sequence via transfer ribonucleic acid (tRNA) within a ribosome

Question 3

Process of transcription

Answer 3

Occurs in nucleus

Hydrogen bonds between DNA strands pulled apart as DNA is ‘unzipped’ by RNA polymerase enzyme

This creates a sense strand and anti-sense strand

Complementary RNA nucleotides are added to anti-sense strand to create mRNA via complementary nucleotide base pairing

mRNA processed to produce mature mRNA

Question 4

Nucleotide categories

Answer 4

Purines

Pyrimidines

Question 5

Purine nucleotides

Answer 5

Adenine (A)
Guanine (G)

Question 6

Pyrimidine nucleotides

Answer 6

Cytosine (C)
Thymine (T) / Uracil (U)

Question 7

Pairings between nucleotides

Answer 7

A <-> T / U

C <-> G

Question 8

Transcription factors

Answer 8

Proteins that bind to specific DNA sequences

Either activators or repressors of RNA polymerase activity to regulate gene transcription to form mRNA

Question 9

Translation process

Answer 9

mRNA crosses nucleus membrane into cytoplasm

mRNA reaches ribosome to be decoded

tRNA brings correct amino acid sequence to mRNA on ribosome via complementary base pairing

tRNA binds to P stie, then next tRNA binds to A site

P site amino acid binds to A site amino acid, ribosome shifts down by one codon and first tRNA is released

Process repeats until ribosome reaches stop codon where ribosome dissociates into subunits and releases mRNA and polypeptide chain

Question 10

Components of 70s ribosome

Answer 10

Smaller 30s ribosome subunit

Larger 50s ribosome subunit

Question 11

Binding sites on 70s ribosome

Answer 11

2 sites to which tRNA carrying amino acids can bind

P site (peptidyl site)

A site (acceptor site)

Question 12

Codon definition

Answer 12

Sequence of 3 nucleotide bases which codes for a specific amino acid

Question 13

Start codon and corresponding amino acid

Answer 13

AUG (if it is the first AUG codon of an mRNA)

Codes for Methionine

Question 14

Stop codon examples

Answer 14

UAA

UAG

UGA

Question 15

Direction of mRNA sequence translation from ribosome

Answer 15

5’ end to 3’ end

Question 16

Anti-codon definition

Answer 16

Corresponding bases on tRNA which are complementary to the codon sequence on mRNA

Question 17

Binding of amino acid to tRNA

Answer 17

Covalent bond at 3’ end

Question 18

Enzymes responsible for loading tRNA with its amino acid

Answer 18

Aminoacyl tRNA synthetases

Question 19

Number of codons

Answer 19

64

Question 20

Number of amino acids

Answer 20

20

Most amino acids have more than one corresponding codon

Question 21

Processing of polypeptide chains formed by translation

Answer 21

Polypeptide leaves ribosome

Goes to Golgi apparatus where it is processed and refined

Resultant protein is packaged and forms secretory granules

Proteins secreted from cell via exocytosis

Question 22

Structure of polypeptides

Answer 22

Primary structure

Secondary structure

Tertiary structure

Quaternary structure (not all proteins have quaternary structure)

Question 23

Primary structure of polypeptides

Answer 23

Sequence of amino acids formed is the primary structure

Amino acids linked via peptide bonds in a condensation reaction

Question 24

Secondary structure of polypeptides

Answer 24

Polypeptide chain acquires geometric shape due to specific patterns of hydrogen bonds that form

Create either Alpha helices or Beta pleated sheets

Question 25

Tertiary structure of polypeptides

Answer 25

Alpha helices or Beat pleated sheets fold to form 3D structures

Caused by various bonding arrangements

Question 26

Quaternary structure of polypeptides

Answer 26

Occurs when more than one polypeptide join together

Not all proteins have quaternary structures

They form Fibrous or Globular proteins

Question 27

Example of Globular protein with quaternary structure

Answer 27

Haemoglobin

Question 28

Structure of Haemoglobin molecule

Answer 28

2 alpha polypeptide chains
2 beta polypeptide chains
Inorganic haem group per polypeptide chain containing Fe2+ ion

Question 29

Abnormality in Sickle Cell Disease

Answer 29

Genetic mutation
Results in abnormal beta chains in Hb which protrude and hooks into neighbouring beta chain

Makes sickle cell Hb molecules lock together and precipitate out of solution

Crystal shapes are formed which leads to sickle shape of RBC

Question 30

Types of genetic mutations

Answer 30

Insertion mutation - nucleotide base is inserted
Deletion mutation - nucleotide base is deleted
Substitution mutation - nucleotide base is replaced with another

Insertion and deletion mutations change all subsequent codons in the sequence until stop codon

Question 31

Type of genetic mutation in sickle cell disease with codon change and amino acid change

Answer 31

Substitution mutation of one codon

GAG (glutamic acid) becomes GTG (valine)

Question 32

Generic action of Oestrogen and Thyroid hormones

Answer 32

Hormones that affect DNA transcription via intracellular nuclear or cytoplasm receptors
Act as transcription factors

Slower to act than those hormones that affect cell membrane receptors