Nucleic acids

Question 1

Draw the structure of a nucleotide

Answer 1

Use google or textbook

Question 2

What are purine bases?

Answer 2

• 2 rings to their structure
• Adenine, guanine

Question 3

What are pyrimidine bases?

Answer 3

• Single ring
• Cytosine, thymine

Question 4

What is the bond between the pentose sugar and phosphoric acid called?

Answer 4

Ester bond

Question 5

Where do phosphodiester bonds form?

Answer 5

Between the sugar and phosphate, creating the sugar phosphate backbone

Question 6

What is the purpose of phosphodiester bonds?

Answer 6

It forms the sugar phosphate backbone of DNA

Question 7

Describe the structure of DNA

Answer 7

• Double helix
• Two polynucleotide chains joined together by organic bases which have a complementary structure to each other.
• The bond that holds bases together= H bonds
• Nucleotides are produced by phosphodiester bonds which is a type of condensation reaction
• Complementary base pairing
• Strands run antiparallel

Question 8

Describe the structure of RNA

Answer 8

• Contains ribose (contains oxygen)
• Single strand
• Contains uracil instead of thymine
• Shorter chain than DNA

Question 9

Name some adaptations of the DNA molecule to its function.

Answer 9

1. It is a stable molecule held together by covalent bonds= not easily broken down, forms the SPBB
2. Able to copy itself accurately= due to complementary base pairing
3. The DNA molecule can fold itself up = Great deal of information can be stored in a small volume
4. Carries information coded in the order of the bases which can be easily copied
5. H bonds are easily broken = Allows replication and protein synthesis
6. H bonds are protected by being on the inside of the molecule = the two SPBB’s give protection to the base sequence from any interference

Question 10

Name some adaptations of RNA to its function.

Answer 10

1. It is single stranded= mRNA can carry a copy of DNA code with the bases exposed
2. It is smaller= can travel out of the nucleus and move around the cell
3. It forms base pairs with the correct tRNA molecule to control the sequence of amino acids in a pp chain

Question 11

Describe semi-conservative replication! (7)

The Highest Fountain Takes It To Africa

Answer 11

1. The DNA double helix is untwisted a bit at a time, catalysed by gyrase enzymes
2. Hydrogen bonds between the nucleotide bases are broken, catalysed by DNA helicase which results in two single strands of DNA with exposed nucleotide bases, kept apart by binding proteins.
3. Free phosphorylated nucleotides are bonded to the exposed bases following complementary base pairing rules. H bonds form, bringing the 2 strand together.
4. The enzyme DNA polymerase joins nucleotides continuously in the 5’-3’ direction, creating the leading strand.
5. In the 3-5 direction, polymerase joins nucleotides in short sections which are later joined by DNA ligase. This is called the lagging strand.
6. The leading strand is synthesised continuously whereas the lagging strand is in fragments (okazarcky fragments)
7. A new strand of DNA has then been formed against each of the old strands so that two identical DNA molecules have been produced.

Question 12

Explain the steps of transcription

Answer 12

1. A gene unwinds and unzips, H bonds break between complementary bases
2. The sense strand runs in the 5-3 direction and contains the code for protein synthesis. The strand in 5-3 is the antisense and it acts as a template.
3. RNA polymerase catalyses the formation of temporary H bonds between RNA nucleotides and the unpaired DNA bases which are complementary to each other.
4. RNA nucleotides are then joined together by phosphodiester bonds using the coding strand. This creates mRNA
5. The mRNA peels off of the coding strand and passes out of the nucleus through the pores in the NE and attaches to a ribosome.

Question 13

Explain the steps of translation

Answer 13

1. Ribosome moves along mRNA until start codon is reached. Then binds to smaller RNA subunit and is held in place until AA sequence is translated.
2. tRNA carries the amino acids to the ribosome
3. tRNA is folded so the anticodon is at one end. The anticodon is the triplet code that will recognise a specific codon in an mRNA molecule.
4. Once the anticodon binds to a complementary codon on the mRNA, the corresponding amino acid joins with the previous amino acid.
5. Continues until stop codon is reached.
6. This forms peptide bonds and creates the primary structure of the protein.

Question 14

What are the 3 features of the genetic code?

Answer 14

• It is near universal, almost all organisms have the same triplet of DNA bases to code for the same amino acids
• Degenerate, there is more than one base triplet that codes for the same amino acid, this reduces chance of damaging mutations
• No overlapping, read from a fixed point in groups of 3 bases (discreet 3’s)

Question 15

How can mutations be caused?

Answer 15

• Spontaneous errors in DNA replication or meiotic recombination
• Radiation, viruses, mutagenic chemicals
• Hypermutation

Question 16

What is dispersive replication?

Answer 16

Part but not all of each strand of the old DNA molecule becomes part of the new ones with bits scattered in amongst the old

Question 17

What is Conservative replication?

Answer 17

A completely new DNA molecule is made with two new strands and the original one stays intact

Question 18

What is Semi-conservative replication?

Answer 18

One new strand of DNA forms against each of the original strands so that each new DNA molecule is made up of one new and one original strand.

Question 19

What does washing up liquid do

Answer 19

Breaks down lipids in phospholipid bilayer of plasma membrane and nuclear envelope so DNA can ‘escape’

Question 20

Why is the solution containing crushed strawberry, salt and washing up liquid placed in a 60C bath?

Answer 20

It speeds up the reaction of washing up liquid and salt

Question 21

What does the salt in the solution do?

Answer 21

Salt is charged as well as DNA, salt breaks the bond between histones so DNA is unravelled.

Question 22

What does ethanol do?

Answer 22

DNA is not soluble in ethanol so it will not dissolve, it is used to separate DNA from the mixture.

Question 23

What does protease do?

Answer 23

• Breaks down histone proteins into amino acids so DNA is released
• Purifies DNA

Question 24

Draw a diagram of ATP

Answer 24

Use google

Question 25

What are the components of ATP?

Answer 25

Ribose, 1-3 phosphates, nitrogenous base

Question 26

What are the properties of ATP?

Answer 26

- Small, useable amount of energy - Easily hydrolysed - Easily transported - Re-phosphorylated= ADP+ another phosphate, ATP (adding phosphates)

Question 27

Name the pentose sugars in DNA and RNA

Answer 27

DNA= deoxyribose RNA= ribose

Question 28

Why is DNA replication described as semi conservative?

Answer 28

- Strands from OG DNA act as templates - New DNA mol contains one old one new strand (base pairing enables genetic material to be conserved accurately)

Question 29

What does DNA helicase do?

Answer 29

Breaks H bonds between base pairs to form 2 single strands

Question 30

How is a new strand formed during SC replication?

Answer 30

1. Free nucleotides from nuclear sap attach to exposed bases by comp base pairing. 2. DNA polymerase joins nucleotides on new strand in a 5-3 direction via condensation reactions (phosphod bonds) 3. H bonds reform

Question 31

What does transcription produce and where does it occur?

Answer 31

- Produces mRNA - occurs in nucleus

Question 32

What happens after a strand of mRNA is transcribed?

Answer 32

- RNA polymerase detaches at terminator region - H bonds reform and DNA rewinds - mRNA moves out of nucleus via NP and attaches to a ribosome

Question 33

What does translation produce and where does it occur?

Answer 33

- produces proteins - occurs in cytoplasm on ribosomes