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AQA - A level Biology > Topic 2 - Nucleic Acids > Flashcards

Topic 2 - Nucleic Acids Flashcards

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1
Q

What structures are made from DNA and where in the cell is DNA found?

A

Chromosomes in the nucleus

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2
Q

How many pairs of chromosomes does a human have in each cell?

A

23 pairs

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3
Q

What type of protein is also contained in chromosones?

A

Histones

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4
Q

What is the basic structure of DNA?

A

Made from two polynucleotide chains arranged in a ladder like structure.
This is known as a double helix.

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5
Q

What are the monomers of DNA and RNA called?

A

Nucelotides

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6
Q

What reaction joins the components of a nucleotide together?

A

Condensation reaction

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7
Q

Name the nitrogenous bases in DNA.

A

Thymine
Adenine
Guanine
Cytosine

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8
Q

What base is replaced in RNA? What replaces this base?

A

Thymine
Uracil

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9
Q

What molecules make up a nucelotide?

A

Pentose sugar
Phosphate group
Nitrogenous bases

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10
Q

How are the two polypeptide chains held together?

A

Hydrogen bonds

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11
Q

What are the two base pairs?

A

A-T
C-G

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12
Q

How many hydrogen bonds form between A-T?

A

2

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13
Q

How many hydrogen bonds form between C-G?

A

3

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14
Q

Describe the process of DNA replication.

A

The enzyme helicase unwinds the DNA double helix by breaking the hydrogen bonds between the base pairs on the two antiparallel polynucleotide DNA strands to form two single polynucleotide DNA strands.
Each of these single polynucleotide DNA strands acts as a template for the formation of a new strand made from free nucleotides that are attracted to the exposed DNA bases by base pairing.
The new nucleotides are then joined together by DNA polymerase which catalyses condensation reactions to form a new strand.
The original strand and the new strand joined together through hydrogen bonding between base pairs to form the new DNA molecule

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15
Q

Why is DNA replication ‘semi-conservative’?

A

This method of replicating DNA is known as semi-conservative replication because half of the original DNA molecule is kept in each of the two new DNA molecules.

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16
Q

How do hydrogen bonds form between water molecules?

A

The oxygen is slightly negative and the hydrogen has a slight positive charge.

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17
Q

How does a high specific heat capacity relate to waters function?

A

Water does not change temperature easily, so acts as a buffer against sudden changes in temperature.

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18
Q

Why is a high specific heat capacity important for living organisms?

A

Buffers organisms against a sudden change in their environment . This makes aquatic environments more stable.

19
Q

Why is a high specific heat capacity important for cellular metabolism?

A

Acts as a buffer so helps enzymes to not be affected by sudden changes in environment.
Maintains an optimum temperature.

20
Q

Why is the latent heat of vaporisation important for water?

A

It requires a very large energy input to change water’s state.

21
Q

Why is water’s surface tension important?

A

Allows some organisms to walk on water.

22
Q

Why is water a good solvent?

A

Because it can get in between and push apart the ions in a compund.

23
Q

Why is water important in metabolism?

A

Water is used to break down complex molecules such as proteins into amino acids by hydrolysis reactions.

24
Q

Name some uses of water.

A

Solvent
Condensation and hydrolysis reactions
Photosynthesis in chloroplasts
Transport medium

25
Q

How is water pulled up through the xylem vessel?

A

There are cohesive forces.

26
Q

What is ATP and what is it made from?

A

Adenine triphosphate
Made from 3 phosphate groups, a ribose sugar and an adenine base.

27
Q

What is the word equation showing the conversion of ATP to ADP?

A

ATP + H20 —–> ADP + Pi

28
Q

What is the word equation for the synthesis of ATP from ADP and Pi?

A

ADP + Pi ——-> ATP + H2O

29
Q

Name the two organelles where ATP is synthesised?

A

Mitochondria and chloroplasts.

30
Q

Name and explain 5 uses of ATP.

A
  1. Activation of molecules - the inorganic phosphate released during hydrolysis of ATP can phosphorylate other compounds in order to make them more reactive. This lowers the activation energy.
  2. Metabolic processes - building and breaking down of macromolecules (starch and polypeptides).
  3. Active transport - used to change the shape of the carrier protein in the plasma membranes. This allows the movement of molecules against their concentration gradient.
  4. Secretion - for the formation of lysosomes.
31
Q

What are the benefits of using ATP as an energy source over glucose?

A

If glucose was used directly, excess energy would be lost as heat.
Why would you use a whole glucose molecule for a reaction when you could use 1 ATP molecule.

32
Q

How does ATP store energy?

A

During cellular respiration glucose is respired to release ‘free energy’.
This ‘free energy’ is used to form a chemical bond joining ADP and Pi to form ATP.

33
Q

Name some examples of inorganic ions.

A

Sodium ions
Potassium ions
Iron ions
Phosphate ions
Calcium ions
Hydrogen ions

34
Q

Where are inorganic ions found?

A

Found in cell cytoplasm and body fluids (e.g blood and urine)

35
Q

What are hydrogen ions used for?

A

Maintains pH. for enzyme controlled reactions in metabolism.

36
Q

What are iron ions used for?

A

Allows oxygen to bind to haemoglobin in red blood cells.

37
Q

What are sodium ions used for?

A

Required for the transport of amino acids and glucose across cell-surface membranes via co-transport.

38
Q

What are phosphate ions used for?

A

Forms phosphate groups.
Bonds between phosphate groups in ATP stores energy.
In DNA and RNA the phosphate groups allow individual nucleotides to join up.

39
Q

What do calcium ions do?

A

In synapses, calcium ions regulate the transmission of impulses from neurone to neurone.

40
Q

What do magnesium ions do?

A

Required for chlorophyll

41
Q

Describe the Meselson-Stahl experiment.

A
  1. Bacteria were grown in a medium containing heavy isotope N-15 for many generations.
  2. Some bacteria were moved to a medium containing light isotope N-14. Samples were extracted after 1 and 2 cycles of DNA replication.
  3. Centrifugation forms a pellet. Heavier DNA (bases made from N-15) settled closer to bottom of tube.
42
Q

How did Meselson and Stahl disprove conservative replication?

A

DNA isolated after one generation (one round of DNA replication) also produced a single band when centrifuged.
However, this band was higher, intermediate in density between the heavy DNA and the light
DNA.
The intermediate band told Meselson and Stahl that the DNA molecules made in the first round of replication was a hybrid of light and heavy DNA.
This result fit with the dispersive and semi-conservative models, but not with the conservative model.
The conservative model would have predicted two distinct bands in this generation (a band for the heavy original molecule and a band for the light, newly made molecule).

43
Q

How did Meselson and Stahl disprove dispersive replication?

A

When second-generation DNA was centrifuged, it produced two bands. One was in the same position as the intermediate band from the first generation, while the second was higher (appeared to be labeled only with N-14.
This result told Meselson and Stahl that the DNA was being replicated semi-conservatively.
The pattern of two distinct bands—one at the position of a hybrid molecule and one at the position of a light molecule—is just what we’d expect for semi-conservative replication.
In contrast, in dispersive replication, all the molecules should have bits of old and new DNA, making it impossible to get a “purely light” molecule.

AQA - A level Biology (5 decks)

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