Nucleotides and Nucleic acids

Question 1

What are nucleic acids?

Answer 1

DNA and RNA

Question 2

What are the monomers of nucleic acids?

Answer 2

Nucleotides

Question 3

What is the structure of a nucleotide?

Answer 3

A phosphate group connected to the 5th carbon of a pentose sugar, connected via the 1st carbon to a nitrogenous base.

Question 4

What different pentose sugars can nucleotides have?

Answer 4

Ribose or deoxyribose.

Question 5

What different nitrogenous (organic) bases can nucleotides have?

Answer 5

Adenine, thymine, cytosine, guanine or uracil.

Question 6

Which nitrogenous bases are purines and which are pyrimidines?

Answer 6

Adenine and Guanine are purines.

Cytosine, Uracil and Thymine are pyrimidines.

Question 7

What is the difference between purines and pyrimidines?

Answer 7

Purines have 2 rings while pyrimidines have only 1.

Pyrimidines bind to purines.

Question 8

Which bases form bonds and how do they bond?

Answer 8

G and C join with 3 hydrogen bonds.

A,T and U join with 2 hydrogen bonds.

Question 9

What kind of reaction joins nucleotides and what bonds are formed?

Answer 9

Condensation reactions attach nucleotides forming phosphodiester bonds between the sugar (3rd carbon) and phosphate of each nucleotide. (forms the sugar-phosphate backbone of the nucleic acid)

Question 10

What is an example of a phosphorylated nucleotide?

Answer 10

ATP and ADP are phosphorylated nucleotides.

ATP is just an adenine nucleotide with 2 extra phosphate groups.

Question 11

Describe the structure of DNA.

Answer 11

2 complementary DNA strands run anti-parallel and are held together by weak hydrogen bonds. These anti-parallel strands twist forming a double helix.

Question 12

What does anti-parallel mean?

Answer 12

The complementary DNA strands run in opposite directions. One is 5’ to 3’ and the other is 3’ to 5’.

Question 13

What is the 5’ (five prime) end of a single DNA stand?

Answer 13

The end which is on the 5th carbon side of the pentose sugars that form the sugar-phosphate backbone.

Question 14

What is the first step in DNA replication?

Answer 14

DNA helicase unwinds and unzips the DNA strands, breaking the weak H-bonds.

Question 15

What is the second step in DNA replication?

Answer 15

DNA polymerase adds free, complementary nucleotides to the strands. Creating the leading and lagging strand.

Question 16

What is the difference between the leading and lagging strand in DNA replication?

Answer 16

The leading strand is continuously copied by DNA polymerase while the lagging strand must be formed in okazaki fragments.

Question 17

Why is there a leading and lagging strand in DNA replication?

Answer 17

DNA polymerase can only add nucleotides to the 3’ end (in the 5’ to 3’ direction).

Question 18

Why is DNA replication called “semi-conservative”?

Answer 18

Each new DNA double helix contains one old strand from the original DNA molecule.

Question 19

What is the nature of the genetic code?

Answer 19

Universal=(codons have the same meaning in all living organisms)
Triplet=(one codon is comprised of 3 nucleotides)
Degenerate=(more than one codon can code for each amino acid)
Non-overlapping=(each nucleotide is only part of one codon)

Question 20

What is the difference in the genetic code between RNA and DNA?

Answer 20

RNA uses uracil instead of thymine.

Question 21

What is a mutation in the genetic code?

Answer 21

A rare, random change in the genetic material, that can be inherited if the mutation affects gametes.

Question 22

What is an example of a harmful mutation?

Answer 22

Sickle cell anaemia (amino acid valine translated instead of glutamate)

Question 23

Why must transcription happen in protein synthesis?

Answer 23

DNA cannot leave the nucleus as it is too large to fit through the nuclear pore. (designed to protect the DNA)

Question 24

How is DNA transcribed in protein synthesis?

Answer 24

Gene is exposed by unwinding and unzipping the double helix with DNA helicase.
RNA polymerase forms a complementary mRNA strand.

Question 25

What is mRNA and what is its purpose?

Answer 25

messenger RNA, takes genetic information from the nucleus to the ribosome.

Question 26

What happens in gene translation?

Answer 26

tRNA brings complementary anticodons and amino acids, which form weak H-bonds with the mRNA in the ribosome.
Peptide bonds form between adjacent amino acids, forming a polypeptide chain of amino acids which detaches from the mRNA as it is formed.

Question 27

What is tRNA?

Answer 27

Transfer RNA, a single codon (anticodon) with the corresponding amino acid attatched.

Question 28

How is the polypeptide chain formed into a protein after translation?

Answer 28

The chain is taken to the golgi apparatus, where it is modified, folded and packed forming a protein.

Question 29

What is rRNA?

Answer 29

Ribosomal RNA, forms part of the ribosome.