TL - DNA, RNA and Protein Synthesis

Question 1

What does DNA stand for?

Answer 1

National Dyslexic Association

just kidding, it’s Deoxyribonucleic Acid

Question 2

What are nucleotides and what are they composed of?

Answer 2

Nucleotides are DNA monomers. They are made of the following:

1) Phosphate group
2) A pentose sugar (Deoxyribose in DNA)
3) A nitrogenous base

Question 3

Name the 4 nitrogenous bases

Answer 3

Adenine
Cytosine
Guanine
Thymine

Question 4

What reaction forms DNA?

Answer 4

The sugar-phosphate backbone is formed by condensation polymerisation

Question 5

Describe the condensation polymerisation of Deoxyribose and a phosphate group

Answer 5

1) The lone pair of electrons on an oxygen atom on the deoxyribose sugar makes a dative covalent bond with the phosphorus atom in a phosphate group
2) A molecule of water is lost and a phosphate-ester link is formed (an ester bond)
3) It’s the other OH groups in the phosphate-ester that enable the nucleotides to bond together in the same mechanism

Question 6

Describe the condensation reaction between the sugar-backbone of a nucleotide to a nitrogenous base

Answer 6

An NH group of a nitrogenous base reacts with the OH group on the 1st Carbon of the deoxyribose molecule, which eliminates an OH group from the sugar and H from the NH group to form water and a glycosidic bond

Question 7

How many types of amino acids are there present in human DNA and why not more?

Answer 7

20

Each amino acid is coded for by a triplet code, but some are coded for by more than one triplet code (degeneracy)

Question 8

Describe the structure of DNA

Answer 8

DNA forms a super-coiled double helix, consisting of 2 strands of DNA joined together by hydrogen bonds between complementary base pairs.

Question 9

State which base pairs with which other base

Answer 9

Adenine - Thymine

Guanine - Cytosine

Question 10

State the number of hydrogen bonds formed between each complementary base pair

Answer 10

Adenine - Thymine : 2 hydrogen bonds

Guanine - Cytosine : 3 hydrogen bonds

Question 11

Describe the process of DNA replication

Answer 11

1) The hydrogen bonds between base pairs are broken by an enzyme and the 2 DNA strands split into 2 single strands
2) Bases of free-floating nucleotides in the cytoplasm complementary base pair to the bases of the nucleotides in the DNA strand
3) The enzyme DNA polymerase joins the new nucleotide together to form a polynucleotide chain
4) This happens on each original strand of DNA, creating 2 molecules of DNA, identical to the original one

Question 12

Describe the importance of the sections of DNA unique to an individual

Answer 12

They can be examined using genetic fingerprinting, which is used to identify people based on sample of DNA, which can be collection from a wide variety of fluid or tissue samples

Question 13

Give 4 ethical considerations about the use of the DNA database

Answer 13

1) There are over a million UK citizens who have never been found guilty of any crime, but who have information about their DNA stored in the database
2) Some people believe this information should be destroyed because it is adding innocent people to a list of criminals
3) Civil rights campaigners argue that people should be able to ask to have their profiles removed - there are concerns about who can access the information and what it could be used for
4) Others believe that the database should include the DNA of everyone who lives in Britain because the information is so useful to the police and has helped solve many crimes

Question 14

What does RNA stand for?

Answer 14

Ribonucleic Acid

Question 15

What is a similarity between DNA and RNA?

Answer 15

They are both polymers of nucleotides, with a series of bases attached to a sugar-phosphate backbone

Question 16

What are some differences between DNA and RNA?

Answer 16

• RNA contain ribose whereas DNA contains Deoxyribose

- RNA has the base Uracil instead of Thymine

Question 17

Name the 3 types of RNA

Answer 17

• mRNA (messenger RNA)
• tRNA (transfer RNA)
• rRNA (Ribosomal RNA)

Question 18

Describe the structure and function of mRNA

Answer 18

• It is a single polynucleotide strand
• It’s an exact reverse copy of a section of DNA (U for T)
• The 3 bases in mRNA that pair up with a base triplet on the DNA strand are called a codon

Question 19

Describe the structure and function of tRNA

Answer 19

• its a single polynucloetide strand that’s folded into a clover shape
• Every tRNA has a binding site at on end, where a specific amino acid attaches
• Each tRNA molecule also has a specific sequence of 3 base, called an anticodon

Question 20

Describe the structure and function of rRNA

Answer 20

It is made up of polynucleotide strands that are attached to proteins to make ribosomes. It is the largest type of RNA

Question 21

Describe transcription

Answer 21

mRNA is made using a DNA template

1) The DNA double helix unwinds to reveal a single stranded portion
2) The DNA bases attract free RNA nucleotides with complementary bases
3) The RNA nucleotides are joined to each other by the enzyme RNA polymerase. This forms a strand of mRNA
4) The DNA coils up agains, unaltered

Question 22

What happens between transcription and translation?

Answer 22

The newly formed mRNA strand moves out of the nucleus, via nuclear pores, and into the cytoplasm

Question 23

Describe translation

Answer 23

Amino acids are joined together to make a polypeptide chain

1) A ribosome attaches to the mRNA and starts to move along it looking for a start codon (AUG)
2) Once it’s found the start codon, the ribosome temporarily pauses, until the tRNA with the correct anticodon bases pairs with the AUG codon inside the ribosome. The tRNA has an amino acid attached to it
3) The ribosome then moves 3 bases forward, and waits for the complementary tRNA to the next codon, which brings the next amino acid into the ribosome, which are joined together by a peptide bond
4) The ribosome moves forwards again. The first tRNA now leaves the ribosome and breaks away from its amino acid. A new tRNA brings the 3rd amino acid of the chain
5) The process continues in this way until a stop codon is reached, which doesn’t code for an amino acid but releases the polypeptide chain at that point