Nucleotides and Nucleic Acids

Question 1

What are nucleotides, and what do they form?

Answer 1

Nucleotides are the monomers that form nucleic acids such as DNA and RNA.

Question 2

How are nitrogenous bases categorized?

Answer 2

Nitrogenous bases are categorized based on their structure and the number of rings: Purines have two rings (adenine and guanine), while Pyrimidines have one ring (cytosine, thymine in DNA, and uracil in RNA).

Question 3

What sugars are found in DNA and RNA?

Answer 3

DNA contains deoxyribose, and RNA contains ribose.

Question 4

What is the complementary base pairing in DNA and RNA?

Answer 4

In DNA, adenine pairs with thymine and guanine pairs with cytosine. In RNA, adenine pairs with uracil instead of thymine.

Question 5

What type of bond forms between nucleotides, and what is the resulting structure called?

Answer 5

A phosphodiester bond forms between nucleotides, creating a polynucleotide chain.

Question 6

What is the function of deoxyribonucleic acid (DNA)?

Answer 6

DNA codes for the sequence of amino acids in the primary structure of proteins, determining their final 3D structure.

Question 7

What is the structure of DNA?

Answer 7

DNA forms a double helix made of two antiparallel strands, held together by hydrogen bonds between complementary bases.

Question 8

What contributes to the stability of the DNA structure?

Answer 8

DNA’s stability comes from the phosphodiester bonds between adjacent nucleotides, creating a sugar-phosphate backbone.

Question 9

Why is the double-stranded structure of DNA advantageous for replication?

Answer 9

It allows both strands to act as templates during DNA replication.

Question 10

How does DNA replication occur, and what makes it semi-conservative?

Answer 10

During DNA replication, one strand is conserved, and a new strand is formed from new nucleotides. This is called semi-conservative replication.

Question 11

What are gene mutations, and when do they occur?

Answer 11

Gene mutations are random, spontaneous changes in the DNA base sequence, which can occur during DNA replication.

Question 12

What are the 3’ prime end and 5’ prime end in a DNA strand?

Answer 12

The 3’ end and 5’ end refer to which carbon in the deoxyribose sugar is exposed at the end of the DNA strand. The 3’ end exposes carbon 3, and the 5’ end exposes carbon 5.

Question 13

Which enzyme catalyzes DNA replication, and where does it bind?

Answer 13

DNA polymerase catalyzes DNA replication, and it binds at the 3’ end of the DNA strand.

Question 14

What is the first step of DNA replication, and which enzyme is involved?

Answer 14

The first step is the breaking of hydrogen bonds between the complementary bases, facilitated by the enzyme DNA helicase.

Question 15

What happens after the DNA strands separate during replication?

Answer 15

Free-floating DNA nucleotides align with their complementary bases on each template strand.

Question 16

How are new DNA strands formed?

Answer 16

Hydrogen bonds form between complementary bases of the new and old strands, and DNA polymerase forms phosphodiester bonds between adjacent nucleotides.

Question 17

What is continuous replication?

Answer 17

Continuous replication occurs on the leading strand, where DNA polymerase can add nucleotides smoothly as the replication fork opens, synthesizing the new strand in a 5’ to 3’ direction continuously.

Question 18

What is discontinuous replication?

Answer 18

Discontinuous replication occurs on the lagging strand, where DNA polymerase synthesizes DNA in small fragments (Okazaki fragments) due to the 5’ to 3’ direction of replication.

Question 19

Why does the lagging strand experience discontinuous replication?

Answer 19

The lagging strand is oriented in the 3’ to 5’ direction, opposite to DNA polymerase’s 5’ to 3’ activity. This requires replication in short fragments as the fork opens.

Question 20

What are Okazaki fragments and how are Okazaki fragments joined together??

Answer 20

Okazaki fragments are short segments of DNA synthesized discontinuously on the lagging strand during replication.
DNA ligase joins the Okazaki fragments by forming phosphodiester bonds between them, creating a continuous DNA strand.

Question 21

What is the difference between the leading and lagging strands?

Answer 21

The leading strand is replicated continuously in the 5’ to 3’ direction, while the lagging strand is replicated discontinuously in the 3’ to 5’ direction through Okazaki fragments.

Question 22

what are the steps of transcription

Answer 22

1) helicase acts on a region of DNA to break the hydrogen bonds between the bases
2) RNA polymerase moves along one of the two DNA strands
3) RNA polymerase matches up complimentary RNA nucleotides
4) C matches G and G matches C, U matches A and A matches T
5) as the RNA nucleotides join the pre-mRNA is formed
6) The DNA behind the RNA polymerase rejoins into a double helix
7) when the RNA polymerase reaches a stop codon, the chain is terminated and the pre-mRNA detaches

Question 23

what is pre-mRNA?

Answer 23

contains non-coding DNA (introns)
exons- the coding parts of DNA
splicosomes- a group of enzymes that carry out splicing to remove the introns from the pre-mRNA turning it into mRNA

Question 24

What does it mean that the genetic code is degenerate?

Answer 24

The genetic code is degenerate because multiple codons can code for the same amino acid, allowing for redundancy in the code.

Question 25

what are the steps of translation

Answer 25

1) mRNA attaches to the ribosome at the ‘start’ codon
2) tRNA attaches to the mRNA with a complimentary anticodon
3) this tRNA brings an amino acid
4) the ribosomes move along the mRNA bringing in 2 tRNA molecules at any one time
5) an enzyme and ATP are used to join the amino acids with a peptide bond
6) the first tRNA is released and can collect another amino acid
7) the process is repeated until a ‘stop’ codon is reached
8) this forms a primary sector protein

Question 26

where does transcription and translation take place

Answer 26

transcription- nucleus
translation- ribosomes (cytoplasm or RER)

Question 27

what is ATP

Answer 27

adenosine triphosphate
it is a store of potential chemical energy

Question 28

how does ATP release energy?

Answer 28

• energy is released when bonds are broken
• a small amount of energy is required to break the bond
• more is then released from breaking it
• ATP is re-synthesised in a condensation reaction using the enzyme ATP synthase

when the bond is broken ADP (adenosine diphosphate) is formed

Question 29

what are the advantages of ATP

Answer 29

• releases energy in small, usable quantities
• easily regenerated
• ATP is a small molecule so it can move through membranes
• contains bonds between the phosphates with intermediate energy
• It’s soluble and unstable so therefore it is not good for storage so energy is stored in carbs and fats which are used as long term storage and are not soluble as they are used for other things in the body (e.g. fats are also used as insulation so therefore cannot be soluble)

Question 30

why is ATP called the universal energy currency?

Answer 30

ATP is the chemical store in every living cell

Question 31

what are the 3 types of mutation?

Answer 31

substitution- least harmful as it still might code for the same amino acid because codons are degenerate
insertion and deletion- causes a frame shift as it has a knock on effect on the rest of the codon. therefore they are more likely to affect the sequence of amino acids (primary structure of the protein)