2.1.3 nucleotides and nucleic acids

Question 1

What are the three main components that make up a nucleotide?

Answer 1

-Pentose monosaccharide
-Phosphate group (-PO4^2-)
-Nitrogenous base

Question 2

What bonds link nucleotides together?

Answer 2

Phosphodiester bonds.

Question 3

What are the purine bases?

Answer 3

-Adenine
-Guanine

Question 4

What are the pyrimidine bases?

Answer 4

-Thymine
-Cytosine

Question 5

What are purines?

Answer 5

The smaller bases, contain single carbon ring structures. (A+G)

Question 6

What are pyrimidines?

Answer 6

The larger bases, contain double carbon ring structures. (T+C)

Question 7

What is the difference between DNA and RNA?

Answer 7

DNA has deoxyribose and RNA has ribose.

Question 8

How are the two strands of the double helix held together?

Answer 8

Hydrogen bonds between the bases-the two parallel strands are arranged in opposite directions.

Question 9

What is the practical for DNA extraction?

Answer 9

-Grind sample to break down cell walls.
-Mix sample with detergent to break down the cell membrane, releasing the cell contains into solution.
-Add salt to break hydrogen bonds between DNA and water molecule.
-Add protease enzyme to break down proteins.
-Add layer of ethanol.
-DNA will be seen as white strands which can be picked up by a glass rod.

Question 10

What base is Thymine replaced with in RNA?

Answer 10

Thymine is replaced with Uracil.

Question 11

What is Semi-conservative replication?

Answer 11

Semi-conservative replication is when two new molecules of DNA are produced, each one consisting of one old strand of DNA and one new strand.

Question 12

What is the role of DNA helicase?

Answer 12

The unwinding and separating of the two strands of the DNA double helix.
-It travels along the DNA backbone, catalysing reactions that break the hydrogen bonds between complementary base pairs.
-‘unzipping’

Question 13

What is the role of DNA polymerase?

Answer 13

Free nucleotides pair with the newly exposed bases on the template strand during ‘unzipping’ process.
-Catalyses the formation of phosphodiester bonds between nucleotides.

Question 14

What is a mutation and how does it occur during DNA replication?

Answer 14

When sequences of bases are not matched exactly and an incorrect sequence may occur, the errors occur randomly and spontaneously and lead to a change in the sequence of bases.

Question 15

What is the genetic code?

Answer 15

DNA must code for a sequence of amino acids.

Question 16

What is the triplet code?

Answer 16

A sequence of three bases, called a codon.
Each codon codes for an amino acid.

Question 17

What is a gene?

Answer 17

A section of DNA that contains the complete sequence of bases to code for an entire protein.

Question 18

What is meant by universal nature of the genetic code?

Answer 18

All organisms use the same code, although sequences of bases coding for each individual protein will be different.

Question 19

What are ‘stop’ codons?

Answer 19

‘Stop’ codons do not code for any amino acids and signal the end of the sequence.

Question 20

How many base triplets or codons are possible?

Answer 20

64 (4 x 4 x 4 or 4^3)

Question 21

What is a ‘start’ codon?

Answer 21

A codon that acts as the start codon when it comes at the beginning of a gene, signalling the start of the sequence that codes for a protein.

Question 22

What is meant by the genetic code being non-overlapping?

Answer 22

Each base in a sequence is read once and is only part of one triplet.

Question 23

What is transcription?

Answer 23

The base sequences of genes are copied and transported to the site of protein synthesis, a ribosome.

Question 24

What is the sense and antisense strand?

Answer 24

Sense strand- only one of the two strands of DNA contains the code for the protein to be synthesised.
Antisense strand- complementary copy of the sense strand and does not code for a protein, and acts as the template strand during transcription.

Question 25

What is the process of transcription?

Answer 25

-Section of DNA that contains the gene unwinds and unzips under control of DNA helicase (hydrogen bonds break).
-Free RNA nucleotides will base pair with complementary bases exposed on the antisense strand when DNA unzips.
-Phosphodiester bonds are formed between the RNA nucleotides by the enzyme RNA polymerase.
-Transcription stops at the end of the gene and the complete short strand of RNA is called messenger (m)RNA.
-The mRNA detaches from the DNA template and leaves the nucleus through a nuclear pore.
-The DNA double helix reforms.
-The mRNA molecule travels to a ribosome in the cell cytoplasm.

Question 26

What is translation?

Answer 26

The ribosome holds mRNA in position while it is decoded, or translated, into a sequence of amino acids.

Question 27

What is the role of ribosomal (r)RNA?

Answer 27

-important in maintaining the structural stability of the protein synthesis sequence and plays a biochemical role in catalysing translation.

Question 28

What is Transfer (t)RNA?

Answer 28

A form of RNA which is necessary for the translation of the mRNA.
-composed of a strand of RNA folded so that the anticodon is at one end of the molecule.

Question 29

What is the process of translation?

Answer 29

-The mRNA binds to the small subunit of the ribosome at its start codon (AUG).
-A tRNA with the complementary anticodon (UAC) binds to the mRNA start codon.
-Another tRNA with the anticodon UGC and carrying the corresponding amino acid, then binds to the next codon on the mRNA (ACG)- a maximum of two tRNAs can be bound at the same time.
-The first amino acid is transferred to the amino acid on the second tRNA by the formation of a peptide bond. This is catalysed by the enzyme peptidyl transferase.
-The ribosome then moves along the mRNA releasing the first tRNA, the second tRNA becomes the first.
Stages 3-5 are repeated with another amino acid added to the chain each time. As the amino acids are joined together forming the primary structure, they fold into secondary and tertiary structures.

Question 30

What is the structure of an ATP molecule?

Answer 30

-A nitrogenous base (adenine).
-A pentose sugar (ribose).
-Three phosphate groups.

Question 31

What is ATP?

Answer 31

Adenosine triphosphate supplies energy needed for synthesis, transport, and movement.
-Universal energy currency.

Question 32

How does ATP release energy?

Answer 32

Hydrolysis reaction to remove a phosphate group.
-produces adenosine diphosphate (ADP) and a phosphate ion, releasing energy.

Question 33

What is the structure of ADP?

Answer 33

-A nitrogenous base (adenine).
-A pentose sugar (ribose).
-two phosphate groups.

Question 34

Why is ATP not a good long-term energy store?

Answer 34

The instability of the phosphate bonds in ATP.

Question 35

What is phosphorylation?

Answer 35

The energy released in the breakdown of fats and carbohydrates is used to create ATP. It occurs by reattaching a phosphate group to an ADP molecule.

Question 36

Why is ATP a good immediate energy story?

Answer 36

The interconversion of ATP and ADP is happening constantly meaning cells do not need a large of store of ATP.

Question 37

What are the properties of ATP?

Answer 37

-Small- moves reality into, out of, and within cells.
-Water soluble- energy-requiring processes happen in aqueous environments.
-Contains bonds between phosphates with intermediate energy: large enough to be useful for cellular reactions but not so large that energy is wasted as heat.
-Releases energy in small quantities- quantities are suitable to most cellular needs, so that energy is not wasted as heat.
-Easily regenerated- can be recharged with energy.