2. Biological functions Part 2

Question 1

List the 3 types of RNA:

Answer 1

• Messenger RNA (mRNA)
• Ribosomal RNA (rRNA)
• Transfer RNA (tRNA)

Question 2

What is messenger RNA (mRNA)?

Answer 2

Molecules that contain the instructions of how to make a peptide chain, and are created by transcription in the nucleus before exiting via a nuclear pore.

Question 3

What does ribosomal RNA (rRNA) and protein form and what is their function?

Answer 3

Form ribosomes which assemble to translate mRNA into protein.

Question 4

What is transfer RNA (tRNA) and what is its function?

Answer 4

Are free-floating molecules in the cytoplasm, in which different tRNA molceules carry a different type of amino acid to ribosomes, where the bottom loop of tRNA contains the anticodon that matches the corresponding mRNA sequence.
-This process is known as translation and forms proteins

Question 5

Describe the 3 stages of transcription

Answer 5

1. Initiation
   - RNA polymerase binds to the DNA at the beginning of a gene at a region called the promoter
2. Elongation
   - RNA polymerase unwraps a small area (around 15 bases of DNA) and starts to add new nucleotides to the DNA template strand according to base pairing rules
3. Termination
   - RNA polymerase continues along the template strand, with new RNA detaching as it is made and DNA re-joining behind it until it reaches a terminal signal

Question 6

What is pre-mRNA and how is it processed?

Answer 6

Newly-made RNA which needs to be processed before leaving the nucleus.
-A methyl cap is added to the 5’ end of the RNA
-A poly-A tail (100-200 adenines) is added to the 3’ end of the RNA
(These additions prevent the RNA from being digested in the cytosol before it can be used)

Question 7

What are exons?

Answer 7

Parts used to make protein

Question 8

What are introns?

Answer 8

Parts which are not needed, which are cut out of the mRNA transcript (not all of the gene is needed in the instructions to make a gene)

Question 9

What is the difference between exons and introns?

Answer 9

EXons EXit the nucleus, whereas INtrons stay IN the nucleus to be recycled.

Question 10

How are variations made to RNA? Give an example:

Answer 10

Instead of just splicing the introns out, some exons can be spliced out as well, which leads to different proteins. (Eg. One protein could contain all exons, and one protein could contain only exons 1,2,4,5,6)

Question 11

What is a codon and how many amino acids and codons are there?

Answer 11

A three-base code in mRNA which codes for a particular amino acid.
-There are 20 different amino acids, and 64 codons

Question 12

Describe the 2 types of codons:

Answer 12

• Start codon AUG: (on mRNA) encodes methionine

- Stop codons UAA, UAG, and UGA: Don’t code for amino acids (no tRNA)

Question 13

Describe the process of translation:

Answer 13

1. Initiation
   - Ribosome binds to the 5’ end of the mRNA and moves to the start codon (AUG).
   - A tRNA enters the ribosome with an anticodon complementary to the mRNA codon and carrying an amino acid.
2. Elongation
   - Every 3 bases the ribosome moves along a new tRNA enters with its amino acid
   - The amino acids are joined together by the ribosome via a peptide bond and the ‘empty’ tRNA exits the other side
3. Termination
   - This continues until a stop codon is reached, where the ribosome will release the mRNA and peptide chain

Question 14

What is transcription?

Answer 14

The process where a gene’s DNA sequence is transcribed (copied) to make RNA.

Question 15

What is RNA polymerase?

Answer 15

The main transcription enzyme.

Question 16

What are genes?

Answer 16

Sections of DNA that contain the instructions to make a single peptide chain

Question 17

What are the small differences between the genes of individuals called?

Answer 17

Alleles

Question 18

What is a genome?

Answer 18

The full DNA sequence of an organism

Question 19

How does DNA replicate itself in a semi-conservative manner?

Answer 19

Each new strand of DNA has one copy of the original and one copy of the new strand, which allows for very accurate replication (high fidelity, few mistakes)

Question 20

What is denaturation?

Answer 20

When the chemical bonds maintaining the 3D shape of the protein break, causing the protein to no longer be able to function as normal.

Question 21

What are nucleic acids?

Answer 21

Are made of nucleotides, where each nucleotide consists of 3 subunits/groups.

Question 22

List the 3 nucleotide groups/subunits:

Answer 22

• Five carbon sugar (Deoxyribose in DNA)
• Negatively charged phosphate group
• Nitrogen base (A, T, G, C)

Question 23

How are nucleotides joined together and where are new nucleic acids added?

Answer 23

Are joined together by a condensation reaction where each nucleotide joins via a phosphodiester bond.
-New nucleic acids are always added to the 3’ end of DNA or RNA strand

Question 24

What are charged tRNA molecules?

Answer 24

tRNA molecules that enter the ribosome with their amino acid

Question 25

What are uncharged tRNA molecules?

Answer 25

‘Empty’ tRNA molecules leaving the ribosome

Question 26

What is gene regulation?

Answer 26

The process of turning gene expression on or off

Question 27

What is the function of regulatory genes and structural genes?

Answer 27

• Regulatory genes are those involved in controlling the expression of one or more genes
• Structural genes are any genes other than regulatory genes

Question 28

Describe the process of proteins being transported out of the cells after translation:

Answer 28

• The proteins made by ribosomes on the rough endoplasmic reticulum are folded and packaged into transport vesicles that are taken into the Golgi apparatus.
• Here, the protein may be modified, before it is once more packed into secretory vesicles for secretion.
• The vesicle containing the secretory proteins fuses with the plasma membrane via exocytosis, releasing the proteins from the cell.