D1.2 Protein Synthesis

Question 1

Define transcription.

Answer 1

The synthesis of RNA using DNA as a template

Question 2

List the roles of RNA polymerases in the process of transcription. ​​

Answer 2

Attaches to DNA
Separates DNA
Produces mRNA molecules and links RNA nucleotides to form a polynucleotide

Question 3

State the complementary base pairing utilized in transcription.

Answer 3

DNA RNA
A U
G C
C G
T A

Question 4

Distinguish between the sense and antisense strands of DNA.

Answer 4

Antisense is the DNA strand, Sense strand is the RNA synthesized strand

Question 5

Define gene expression.

Answer 5

The process by which genetic information in a gene (sequence in DNA) is used to synthesize a functional polypeptide

Question 5

Outline how stability of the information stored in DNA is maintained.

Answer 5

Due to the strong covalent bonds between the nucleotides

Question 6

Outline the major steps of gene expression.

Answer 6

Transcription : synthesis of RNA using DNA as a template
Translation : synthesis of polypeptides by ribosomes using genetic code of mRNA

Question 7

Outline the role of transcription in regulating gene expression.​

Answer 7

Limit the amount of mRNA that is produced by a gene

Question 7

State that the pattern of gene expression is how cells differentiate for specific functions.

Answer 7

Pattern of gene expression is how cells differentiate for specific functions

Question 8

Outline the roles of mRNA, ribosomes and tRNA in translation.

Answer 8

mRNA binds to small subunit of ribosome to initiate translation
tRNA transfers amino acids from cytoplasm to ribosome
Ribosomes translate genetic code of mRNA into polypeptide

Question 8

Define translation.

Answer 8

The synthesis of polypeptides through ribosomes

Question 9

Describe the structures of mRNA and tRNA.

Answer 9

mRNA contains genetic code in form of codons (sequence of three nucleotides )
tRNA have an anticodon to bind to mRNA codons

Question 9

State the location of translation in cells.​

Answer 9

At the ribosomes in the cytoplasm

Question 10

Describe the structure of the ribosomes, including the small and large subunits and the names and roles of the tRNA binding sites.

Answer 10

Ribosomes are organelles composed of a small and large subunit and has three sites for tRNA called Peptidyl site, Aminoacyl site, Exit site and one site for mRNA
A site : tRNA brings a new AA into the ribosome to be added to the elongating polypeptide chain
P site : Holds tRNA with growing polypeptide chain and peptide bond is formed between the AA of the P and A site, releases the tRNA into the E site
E site : After tRNA enters the E site, it’s released from the ribosome.

Question 11

State the complementary base pairing utilized in translation.

Answer 11

Cytosine Guanine
Adenine Uracil

Question 12

Describe the formation of hydrogen bonds between codon and anticodon.

Answer 12

They use the complementary base pairing to form h-bonds

Question 13

Define codon and anticodon.

Answer 13

Codon sequence of three nucleotides in mRNA that determine position of AA when a cell starts making a protein
Anticodon sequence of three nucleotides in tRNA that binds to corresponding codon and designates a specific AA

Question 14

Explain the reason that a sequence of three nucleotides is required to code for the 20 amino acids commonly utilized by organisms.

Answer 14

Three nucleotides can form 64 different codons which codes for 20 different AA

Question 15

Define codon, degenerate and universal as related to the genetic code.

Answer 15

Codon : sequence of three nucleotides in mRNA that determine position of AA when a cell starts making a protein
Degenerate : more than one codon may code for the same AA
Universal : all life forms use genetic code

Question 16

Outline the process of translation elongation, including codon recognition, bond formation and translocation.

Answer 16

Ribosome moves along mRNA from codon to codon through translocation
At each codon tRNA enters the ribosome and forms an AA through codon recognition
When two tRNAs are present in the ribosome, a peptide bond forms between their AA
The polypeptide chain grows till a stop codon enters the ribosome

Question 17

State the cause of sickle cell anemia, including the differences in the HbA and HbS alleles.

Answer 17

Single base substitution mutation for the alpha globin molecule of haemoglobin from an HbA allele which causes no problem to the HbS allele causing sickle cell trait.

Question 18

Define gene mutation.

Answer 18

Change to DNA sequence of an organism

Question 19

State the difference in RNA sequences in the transcription of the HbA and HbS alleles.

Answer 19

HbA has a glutamate as the 6th AA and HbS a valine as the 6th AA

Question 20

State the difference in amino acid sequences in the translation of the HbA and HbS alleles.

Answer 20

HbA has a glutamate and HbS a valine

Question 21

Outline the consequences of the HbS mutation on the structure and function of the hemoglobin protein.

Answer 21

HbS mutation alters structure and function of hemoglobin causing red blood cell sickling

Question 22

Describe the formation of the covalent bond between adjacent nucleotides during transcription.

Answer 22

The C-5 of a nucleotide is added to the C-3 end of the preceding nucleotide to form a phosphodiester (covalent) bond

Question 23

Discuss the symptoms of sickle cell disease.

Answer 23

Blocks small blood vessels

Question 24

State the direction of movement of the ribosome along the mRNA molecule.

Answer 24

During translation ribosome goes from 5’ to 3’

Question 24

State that RNA polymerases can only add the 5’ phosphate of a free nucleotide to the 3’ deoxyribose of the elongating strand.​

Answer 24

RNA polymerases can only add the 5’ phosphate of a free nucleotide to the 3’ deoxyribose of the elongating strand.

Question 25

Outline the structure and function of the promoter regions of DNA.

Answer 25

A non-coding section of DNA where RNA polymerase binds to initiate transcription of a gene.

Question 26

Describe the initiation of transcription, including the role of the promoter sequence, transcription factors and RNA polymerase.

Answer 26

At the promoter region, proteins such as transcription factors can bind in the correct orientation to allow RNA polymerase to also bind and to the promoter sequence and initiate transcription

Question 27

Compare the function of activator and repressor sequences within the promoter.

Answer 27

Activator sequences promote gene expression and repressor sequences prevent gene expression

Question 28

State that transcription factors are proteins that bind to the promoter.

Answer 28

Transcription factors are proteins that bind to the promoter

Question 29

Outline the location and timing of post-transcriptional modification of RNA.

Answer 29

post-transcriptional modification of RNA occurs in the nucleus and cytosol.

Question 29

Describe the function of the 5’ cap and poly-A tail.

Answer 29

To stabilize the mRNA a cap is added to the 5’ end and a poly-A-tail is added to the 3’ end.

Question 29

Define “coding” and “non-coding” sequences of DNA.

Answer 29

Coding DNA : gene sequences that code for mRNA and are expressed as functional polypeptides Non-coding DNA : sections of DNA that do not code for functional polypeptides

Question 30

State that some transcription factors activate transcription while others inhibit transcription.

Answer 30

Some transcription factors activate transcription while others inhibit it

Question 31

Outline five functions of noncoding DNA sequences found in genomes.

Answer 31

Telomeres : repetitive base sequences at the ends of chromosomes. When DNA gets replicated, sequences at the end are lost, telomeres prevent important genes from being lost. Regulators of gene expression : DNA sequences that regulate gene expression such as promoters (sequences that occur just before genes and act as a binding point for RNA polymerase) Enhancers : dna sequences that are binding sites for proteins that increase the rate of transcription Silencers : dna sequences that are binding sites for proteins that decrease the rate of transcription Introns : sections of DNA or RNA that do not code for a protein and interrupt gene sequence

Question 32

Compare intron and exon sequences of genes.

Answer 32

Exons code for a polypeptide chain however introns need to be removed from RNA molecule

Question 33

Outline the process of RNA splicing. ​

Answer 33

Spliceosomes attach to both ends of an intron and cut it out. Exons are then spliced together to form mature mRNA.

Question 34

Describe the process of alternative RNA splicing.

Answer 34

Combines exons in various ways, creating diverse mRNA transcripts proteins from a single gene

Question 35

Outline the benefit of alternative RNA splicing.​

Answer 35

Allows a single gene to produce multiple different mRNA transcripts

Question 36

Outline the process of translation initiation.​

Answer 36

Small ribosomal subunit binds to the mRNA at the start codon tRNA molecule with anticodon complementary to start codon binds to the mRNA Large ribosomal subunit binds to small ribosomal subunit tRNA is in P site, a second codon enters the A site A tRNA complementary to second codon enters the A site Peptide bond between two AA forms.

Question 37

Outline the two stages of modification of preproinsulin to form functional insulin.​

Answer 37

Formation of proinsulin : a single peptide is removed from preproinsulin within the RER to form proinsulin Formation of insulin : proinsulin sent to the golgi apparatus, and is packaged into a secretory vesicle, within the secretory vesicle, a protein chain is removed from proinsulin to form an alpha and beta chain. Alpha and beta chain join by disulfide bonds to form functional insulin

Question 37

List reasons when proteins typically exist for a relatively short time within a cell.

Answer 37

Because as soon as they aren’t required proteasomes recycle to them so they form required proteins.

Question 38

Outline the function of proteasomes in the recycling of amino acids.

Answer 38

Break down unneeded proteins to amino acids through hydrolysis and AAs are then recycled to synthesize proteins required by the cell