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OCR Biology > ✨Module 2: Nucleic acids > Flashcards

✨Module 2: Nucleic acids Flashcards

(50 cards)

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1
Q

Basic unit of the polymer nucleic acids?

A

Nucleotides.

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2
Q

Nucleotides are composed of a …

A

Pentose sugar, phosphate group and nitrogenous base.

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3
Q

Sugar component in DNA nucleotides?
Sugar component in RNA nucleotides?

A

Deoxyribose
Ribose.

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4
Q

DNA is a …
RNA is a …

A

Double stranded molecule.
Single stranded polymer of nucleotide monomers/single helix.

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5
Q

How do nucleotides link together?

A

Condensation reaction to form a polynucleotide. The phosphate group at the 5’ (carbon 5) end of one nucleotide and the OH group on the 3’ end of another nucleotide form phosphodiester bonds (type of covalent bond). This releases a water molecule.

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6
Q

Pyramidines have …
Purine have …

A

1 nitrogen containing ring.
2 nitrogen containing rings.

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7
Q

3 examples of pyramidines?
2 examples of purines?

A

CUT
AG

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8
Q

Describe the structure of DNA.

A

-> 2 strands of polynucleotides that are antiparallel.

-> These 2 strands coil into the double helix, and there are hydrogen bonds between complementary base pairs.

-> This double strand makes DNA stable.

-> Each strand has a phosphate group at one end (5’) and a hydroxyl group at the other (3’).

-> The pairing of bases allows DNA to be copied and transcribed.

-> Polymer so has a lots of information.

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9
Q

Adenine and thymine form …
Cytosine and guanine form …

A

2 hydrogen bonds.
3 hydrogen bonds.

This means that a small pyramidine base always binds to a larger purine base.

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10
Q

DNA replication.

A

-> DNA helicase breaks the hydrogen bonds between comp. base pairs to form 2 single DNA strands.

-> Each strand acts as a template and DNA polymerase brings free nucleotides (have 3 phosphate groups and 2 break off to release energy for this reaction) and catalyse the formation of phosphodiester bonds between adjacent nucleotides in a condensation reaction.

-> DNA ligase then binds to the DNA molecule and catalyses the formation of phosphodiester bonds between adjacent nucleotides in the gaps that DNA polymerase has missed (Okazaki fragments).

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11
Q

Why is DNA replication called semi-conservative?

A

Each new DNA molecule contains one original and new strand.

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12
Q

Codons are non-overlapping which means …

A

Successive triplets are read in order and each nucleotide is part of 1 codon. Each base is only read once.

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13
Q

What is the genetic code?

A

Three bases that is equivalent to one codon. One codon codes for one amino acid. Instructions that tell a cell how to make a specific protein.

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14
Q

Why is the genetic code universal?

A

All known organisms use the same 4 nucleotide bases. Organisms differ according to the arrangement of nucleotide bases.

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15
Q

What is a gene?

A

Section of DNA that contains the complete sequence of bases (codons) that code for an entire protein.

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16
Q

Why is ATP called the universal energy currency?

A

It is present in all cells, it is present in all organisms, it releases energy in small quantities.

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17
Q

ATP is made up of …

A

Nucleotides bonded together. Contains the base adenine, pentose sugar ribose and 3 inorganic phosphate groups.

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18
Q

How does ATP release energy? Give the equation for this.

A

The removal of phosphate group by HYDROLYSIS releases LOTS of energy required by cells for chemical reactions.
ATP + H2O = ADP + Pi + energy

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19
Q

How is ATP produced? Give the equation for this.

A

Energy SUPPLIED from respiration is used to:
ADP + Pi + energy = ATP + H2O.
This is a phosphorylation/condensation reaction.

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20
Q

What are some properties of ATP that help its function?

A

Small so can be moved easily.
Water soluble due to charged phosphate groups attract water and the hydroxyl groups on ribose can form hydrogen bonds with water molecules.
Contains unstable bonds between phosphates so lots of energy is released when broken.

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21
Q

Why is ATP a good IMMEDIATE energy store but not long term energy store?

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A

Not good for long term due to the instability of the phosphate bonds.

22
Q

What does ATP hydrolase do?

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A

Catalyses the breakdown of ATP into ADP and inorganic phosphate group (Pi) through hydrolysis.
This releases LOTS of energy needed by cells due to breakdown of phosphate group.

23
Q

What can happen to this Pi molecule?

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A

It can be added to other molecules to increase their reactivity.

24
Q

What does ATP synthase do?

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A

Phosphorylation (adding a phosphate increases the molecule’s reactivity). ATP is regenerated by combining ADP and Pi.

25
What are the 3 types of RNA involved in protein synthesis? (Remember all of this has U instead of T)
tRNA, mRNA, rRNA (inside ribosome).
26
What is mRNA?
Single polynucleotide chain made in the nucleus during transcription. Group of 3 adjacent bases in mRNA are called codons.
27
What is the link between DNA and mRNA?
mRNA has the complementary base sequence to DNA.
28
What is rRNA?
Forms 2 subunits in the ribosome. The ribosome moves along the mRNA strand during protein synthesis. rRNA in the ribosome catalyses the formation of peptide bonds between amino acids.
29
What is tRNA?
1 polynucleotide strand that is folded into a clover shape. Hydrogen bonds between specific base pairs hold the molecule in this shape.
30
Amino acids is bound to tRNA by ...
Ester bonds.
31
What is the anti-codon (on one end of tRNA)? What is on the other end of tRNA?
Region of complementary base pairs to bind to potential codons. Where the amino acid is.
32
Ribosomes are made up of ...
Proteins and rRNA. It is only involved in translation to convert mRNA to polypeptide chains.
33
If there are 4 bases, how many possible amino acids could be coded for?
4x4x4 = 64 as 3 bases code for 1 amino acid and each base there are 4 possibilities.
34
Why are codons degenerate?
Multiple codons can code for the same amino acid in protein synthesis. There are 20 amino acids but 64 possible codons.
35
What happens in cellular respiration?
Glucose is broken down into ATP, allowing us to use the energy stored in ATP for metabolic processes.
36
Explain what happens in transcription in protein synthesis.
-> DNA helicase breaks the hydrogen bonds between the two DNA strands, exposing the bases on each strand. One of the strands, the antisense strand, act as a template. -> RNA polymerase binds in a region just before the start codon of the gene and transcribes DNA to mRNA. It reads the nucleotides on the unwound template strand from 3' to 5'. The growing mRNA strand forms in 5’ to 3’. RNA polymerase lines up free RNA nucleotides along the template/antisense strand. Complementary base pairing where T is replaced by U. RNA polymerase stops transcribing mRNA once it reaches the stop codon. -> RNA polymerase catalyses the formation of phosphodiester bonds between RNA nucleotides. -> Hydrogen bonds between uncoiled strands of DNA reform after RNA polymerase has read it. It coils back to double helix. -> mRNA leaves nucleus and moves out of nuclear pore to the ribosome in cytoplasm.
37
Where does transcription happen?
In the nucleus.
38
Why is DNA transcribed to mRNA?
DNA is too large to leave the nucleopores to the ribosome.
39
Explain what happens in translation in protein synthesis.
-> mRNA attaches to ribosome and tRNA carries amino acids to the ribosome. tRNA with the complementary anticodon to the start of mRNA, attaches to mRNA by complementary base pairing and so do the other tRNA. -> rRNA catalyses the formation of peptide bonds between amino acids. First tRNA moves away, leaving the amino acid behind in the correct sequence. This keeps happening until there is a stop codon on mRNA. This forms the primary structure of the protein coded for by the mRNA. -> Polypeptide chain (protein) moves away from ribosome.
40
Where does translation happen?
In the ribosome in cytoplasm.
41
Why might a mutation in non-coding DNA affect the phenotype?
Before transcription, RNA polymerase has to bind to region of non-coding DNA in front of a gene. If there's a mutation here, it could affect RNA polymerases ability to bind to it.
42
PAG: Purification/extraction of DNA by precipitation.
1. Grind the sample in a pestle and mortar to break down the cell wall. Add detergent, salt. 2. Cool mixture by putting in ice bath for 5 mins. 3. Blend mixture for 5 secs to degrade the cell walls/membranes further, so DNA is released. 4. Filter the mixture and ensure no contamination of foam in filtrate. 5. Add 2-3 drops of protease to the filtrate in a boiling tube and mix. 6. Pour ice cold ethanol down the side to form a layer.
43
What is the purpose of detergent?
It degrades the membrane/phospholipids, releasing the DNA and cell contents.
44
What is the purpose of salt?
Salt breaks the hydrogen bonds between the negatively charged phosphate group in the DNA and the water molecules.
45
Why should the temperature throughout this experiment stay low?
It reduces the activity of enzymes so reduces the breakdown of DNA.
46
Why add the protease enzyme?
Protease denatures the histones associated with DNA. This allows it to hydrolyse the peptide bonds.
47
Why do we add ethanol to the top of the sample?
Alcohol causes the DNA to precipitate out of the solution.
48
DNA replication concerning Okazaki fragments.
DNA polymerase moves through the leading strand from 3’ to 5’. But as helicase unwinds, the dna polymerase moves from 3’ to 5’ end from the lagging strand in the opposite direction. As helicase unwinds, dna polymerase keeps moving back towards the intersection and causes Okazaki fragments on the lagging strand. The DNA ligase forms the nicks between the Okazaki fragment.
49
Explain how a change in DNA bases could result in a non-functional enzyme.
Change in sequence of amino acids, alters tertiary structure/active site of enzyme, substrate can't bind.
50
Explain how structure of DNA is related to its function.
=> Sugar phosphate backbone gives strength/stability. => Coiling gives compact shape. => Large molecule stores lots of information. => Chains can split for replication. => Double helix protects weak hydrogen bonding.

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