Foundation 1 Questions 13-26

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Question 13

Which of the following describes the secondary structure of proteins?

  1. Multiple polypeptide chains forming a protein complex
  2. An addition of an inorganic group onto the protein complex
  3. A 3D structure formed by non-covalent interactions and hydrophobic clustering
  4. Polypeptide chains with beta pleated sheets and alpha-helices that are stabilised by hydrogen bonds
  5. Linear sequence of amino acids in a polypeptide chain

The correct answer is option d. Polypeptide chains with beta pleated sheets and alpha-helices that are stabilised by hydrogen bonds

Correct Answer Explanation – Correct this is secondary structure
a. Incorrect this is quaternary structure
b. Incorrect this is post translational modification
c. Incorrect this is tertiary structure
e. Incorrect this is primary structure

Question 14

Which of the following is incorrect regarding post-transcriptional modification of mRNA?

  1. snRNPs remove exon sequences
  2. 5’ cap is added to distinguish mRNA from other RNA
  3. snRNPs remove intron sequences
  4. Polyadenylation prevents degradation 
  5. Proteins needed for translation are recruited to the 5’ cap

The correct answer is option a. snRNPs remove exon sequences

Correct Answer Explanation – Correct this is false as during splicing snRNPs remove intron sequences
b. Incorrect, this is true
c. Incorrect, this is true
d. Incorrect, this is true
e. Incorrect, this is true

Question 15

During the post-transcriptional processing of RNA what molecule is added to the 5’ end to prevent degradation by exonucleases?

  1. Poly – A tail
  2. 5-trimethylguanosine cap
  3. 6-methylcytosine cap
  4. 7-methylguanosine cap
  5. 6-trimethylguanosine cap

The correct answer is option d. 7-methylguanosine cap

Correct Answer Explanation – The 5’ cap is made of 7-methylguanosine
a. Incorrect this is added to 3’ end
b. Incorrect
c. Incorrect
e. Incorrect

Question 16

Which of the following denotes a stop codon on the mRNA?

  1. AUG
  2. UAG
  3. UCA
  4. UUU
  5. TAC

The correct answer is option b. UAG

Correct Answer Explanation – Correct, UAG, UGA and UAA are stop codons
a. Incorrect AUG (methionine) is the start codon
c. Incorrect
d. Incorrect
e. mRNA does not have thymine

Question 17

Which two nitrogenous bases form 2 hydrogen bonds between opposing DNA strands?

  1. A + C
  2. A + T
  3. C + G
  4. A + C
  5. A + U

The correct answer is option b. A + T

b. is correct as A and T are coplimentary bases which has 2 H-bonds
a. Incorrect, these do not pair together 
c. Incorrect, linked by 3 H bonds
d. Incorrect, these do not pair together 
e. Incorrect is found in RNA not DNA (although does have 2 H bonds)

Question 18

A silent mutation is unlikely to affect the end protein because…

  1. Multiple codons can code for the same aa
  2. The silent mutation does not cause frameshift
  3. The dominant allele can compensate for the silent mutation
  4. The post translational modifications create a protein with similar properties
  5. The silent mutation substitutes an aa with similar properties

The correct answer is option a. Multiple codons can code for the same aa

Correct Answer Explanation – Correct as silent mutations often occur in the last base of the codon and since multiple codons code for the same aa, the same aa is often added
b. Incorrect, although this is true it is not the ‘best answer’
c. Incorrect
d. Incorrect
e. Incorrect the silent mutation normally keeps the same aa

Question 19

Which of the following is Correct regarding translation?

  1. DNA polymerase binds the RNA chain together 
  2.  No tRNAs recognise the stop codon 
  3. Ribosomes move along mRNA in the 3’ to 5’ direction
  4. No ambiguity means there may be multiple codons for one amino acid 
  5. The anticodon loop in tRNA contains a ribosome binding site 

The correct answer is option b.  No tRNAs recognise the stop codon 

Correct Answer Explanation – Correct it is the release factor that recognises stop codon so that the completed polypeptide is released
a. Incorrect, RNA polymerase binds the RNA chain together
c. Incorrect, ribosomes move along mRNA 5’ to 3’
d. Incorrect, no Ambiguity means no single codon codes for more than one amino acid. There is some redundancy which means there may be multiple codons for one amino acid.
e. Incorrect, the ribosome binding site is in the 5’ UTR of mRNA

Question 20

Which of the following is not true of nucleic acids?

  1. DNA consists of two antiparallel strands
  2. The bases Adenine and Guanosine both contain nitrogenous rings
  3. Introns in mRNA have some functions in the genome
  4. All exons will appear in the coding strand of RNA
  5. Amino acids are transferred on to tRNA by the enzyme peptidyl transferase

The correct answer is option e. Amino acids are transferred on to tRNA by the enzyme peptidyl transferase

Correct Answer Explanation – Correct this is untrue, amino acids are transferred on to tRNA by amino-acyl-tRNA-synthetase. Peptidyl transferase creates peptide bonds between amino acids to form the final polypeptide.
a. Incorrect this is true, as one strand has direction 5’ to 3’ and the other 3’ to 5’
b. Incorrect this is true.
c. Incorrect this is true, although not translated into the final protein, introns are involved in regulating the mRNA 
d. Incorrect as amino acid strands can be modified to remove some exons 

Question 21

Which organelle translates membrane and secretory proteins?

  1. Golgi apparatus
  2. Cytosol
  3. Nucleus
  4. Smooth ER
  5. Rough ER

The correct answer is option e. Rough ER

Correct Answer Explanation – Correct, membrane and secretory proteins are translated at ribosomes that are moved to the Rough ER so they are in close proximity to the Golgi for modification and packaging
a. Incorrect this sorts and modifies proteins
b. This is where ribosomes are found
c. Incorrect this contains genetic material and is the site of transcription
d. Incorrect this is the site of lipid synthesis

Question 22

What enzyme is responsible for adding RNA primers to help the synthesis of the lagging strand during DNA replication?

  1. RNA primase
  2. RNA polymerase
  3. DNA primase
  4. DNA helicase
  5. RNA helicase

The correct answer is option c. DNA primase

Correct Answer Explanation – Correct
a. Incorrect is DNA primase
b. Incorrect this is involved in adding complementary base pairs during transcription 
d. Incorrect this unwinds the DNA during DNA replication
d. Incorrect these are used in RNA metabolism

Question 23

Methotrexate is an antimetabolite which inhibits an enzyme essential for DNA replication. With which phase of the cell cycle does methotrexate interfere? 

  1. G0 phase
  2. G1 phase
  3. S phase
  4. M phase
  5. C phase

The correct answer is option c. S phase

Correct Answer Explanation – DNA replication occurs in the S Phase so that is where methotreate is most likely to affect
a. Incorrect as G0 phase is the part of the cell cycle where growth ceases 
b. Incorrect as the G1 phase does not have DNA replication
d. Incorrect as the M phase does not have DNA replication 
e. Incorrect as the C phase does not have DNA replication

Question 24

Which of the following is the correct description of an anchoring junction in epithelial cells?

  1. Adherens junctions attach to intermediate filaments laterally between cells
  2. Desmosomes attach to actin filaments inferiorly between the cell and the basal lamina
  3. Focal adhesions attach to actin filaments inferiorly between the cell and the basal lamina
  4. Hemidesmosomes attach to intermediate filaments laterally between cells
  5. Focal adhesions attach intermediate filaments between the cells and basal lamina

The correct answer is option c. Focal adhesions attach to actin filaments inferiorly between the cell and the basal lamina

Correct Answer Explanation – Think of the four types of anchoring junctions in two categories – which filaments they attach to and where they attach. The ones with an a in them attach to actin, i.e. adherens, focal adhesions.
a. Adherens junctions use actin filaments not intermediate filaments
b. Desmosomes attach laterally between cells using intermediate filaments
d. Hemidesmosomes attach between cells and basal lamina using intermediate filaments
e. Focal adhesions use actin, not intermediate filaments

Question 25

A 1-year-old boy has a severe skin condition where the epidermis and dermis separate with minor trauma. Which of the following cell junctions is most likely to be defective?

  1. Hemi-desmosomes
  2. Gap junctions
  3. Desmosomes
  4. Tight/Occluding junctions
  5. Adherens Junctions

The correct answer is option a. Hemi-desmosomes

Correct Answer Explanation – Correct these attach the cell to the underlying basal lamina which is part of the basement membrane that acts as an interface between the dermis and epidermis
b. Incorrect these form channels for diffusion between cells and are more to do with cell-cell communication
c. Incorrect these attach cell to cell not cell to basal lamina
d. Incorrect these prevent passage of molecules between cells and give polarity
e. Incorrect these attach cell to cell not cell to basal lamina

Question 26

Which of the following processes uses the hydrolysis of ATP?

  1. Movement of oestrogen into a cell
  2. Movement of water through aquaporins
  3. Co-transport of sodium and glucose into a cell
  4. Pumping sodium out of a cell and potassium in
  5. Opening of VGSC

The correct answer is option d. Pumping sodium out of a cell and potassium in

Correct Answer Explanation – Incorrect steroid hormones can passively diffuse into a cell down their concentration gradient
a. Incorrect this is an example of facilitated diffusion which doesn’t use ATP
b. Incorrect this is an example of secondary active transport which uses the energy generated by moving one molecule down its concentration gradient to move another molecule against its concentration gradient
c. Correct this is done by the Na+ gradient which does not use ATP to pump these molecules against their concentration gradients
e. Incorrect, this is due to the change in voltages