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biological molecules esq Flashcards

1
Q

Describe the structure of DNA. (5)

A
  1. Polymer of nucleotides;
  2. Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
  3. Phosphodiester bonds (between nucleotides);
  4. Double helix/2 strands held by hydrogen bonds;
  5. (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;
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2
Q

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule. (2)

A

-Condensation (reaction)/loss of water

-Between)phosphate and deoxyribose

-Catalysed by DNA polymerase

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3
Q

Describe the role of DNA polvmerase in the semi-conservative replication of DNA.( 2)

A

-Joins (adjacent DNA) nucleotides;

-(Catalyses) condensation reactions

-phosphodiester bonds between adjacent nucleotides

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4
Q

Use your knowledge of semi-conservative replication of DNA to suggest:
1. the role of the single-stranded DNA fragments
2. the role of dna nucleotides

A

•Role of single-stranded DNA fragments
-Template
-Determines order of nucleotides/bases

•Role of DNA nucleotides
-Forms complementary pairs

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5
Q

Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA (2)

A

-easily broken hydrogen bonds between bases allow two
strands to separate
-Two strands, so both can act as templates

-Complementary base pair allows accurate replication;

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6
Q

Describe the role of two named enzymes in the process of semi-conservative replication of DNA (3)

A

-DNA helicase causes breaking of hydrogen between DNA strands

-DNA polymerase joins the nucleotides;

-Forming phosphodiester bonds

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7
Q

The enzymes DNA helicase and DNA polymerase are involved in DNA replication.
Describe their function (2)

A

-DNA helicase unwinding DNA and
breaking hydrogen bonds

-DNA polymerase - joins (adjacent)
nucleotides OR forms phosphodiester bond

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8
Q

Adenosine triphosphate (ATP) is a nucleotide derivative
Contrast the structures of ATP and a nucleotide found in DNA to give two differences. (3)

A

-ATP has ribose and DNA nucleotide has deoxyribose

-ATP has 3 phosphate groups and DNA nucleotide has 1 phosphate group

-ATP - base always adenine and in DNA nucleotide base can be different

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9
Q

use your knowledge of enzyme action to explain why the arrows point in opposite directions (4)

A

-DNA polymerase

-specific

-Only complementary with / binds to 5’ end of strand

-Shapes of 5’ end and 3’ end are different

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10
Q

Describe how an ATP molecule is formed from its component molecules. (4)

A

-adenine, ribose, three phosphates
- condensation reaction
-atp synthase

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11
Q

The new antibiotic is safe to use in humans because it does not inhibit the
ATP synthase found in human cells.
Suggest why human ATP synthase is not inhibited and bacterial synthase
is inhibited.(1)

A

-Human ATP synthase has a different shape active site to bacterial ATP synthase

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12
Q

ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use. (2)

A

-Releases relatively small amount of energy
-energy is readily available

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13
Q

Cells constantly hydrolyse ATP to provide energy.
Describe how ATP is resynthesised in cells. (3)

A

-From ADP and phosphate;
-By ATP synthase
-During respiration

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14
Q

Give two ways in which the hydrolysis of ATP is used in cells. (2)

A

-To provide energy for other reactions
-To add phosphate to other substances and make them more reactive/change their shape

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15
Q

Explain five properties that make water important for organisms. (5)

A

A metabolite in condensation/hydrolysis/ photosynthesis/respiration;

A solvent so (metabolic) reactions can occur

High (specific) heat capacity so buffers changes in temperature

Large latent heat of vaporisation so provides a cooling effect (through evaporation);

Cohesion (between water molecules) so supports columns of water (in plants);

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16
Q

Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. (3)

A

-Substrate binds to the active site/enzyme

-Active site changes shape (slightly) so it is complementary to substrate

-Reduces activation energy;

17
Q

A competitive inhibitor decreases the rate of an enzyme-controlled reaction.
Explain how. (3)

A

-Inhibitor similar shape to substrate

-Fits/binds to active site

-Prevents/reduces enzyme-substrate complex forming

18
Q

Describe how the structure of a protein depends on the amino acids it contains. (5)

A

-Structure is determined by (relative) position of amino acid/R group/i

-Primary structure is sequence/order of amino acids

-Secondary structure formed by hydrogen bonding (between amino acids)

-Tertiary structure formed by interactions (between R groups)

-Creates active site in enzymes

19
Q

Explain how the active site of an enzyme causes a high rate of reaction. (3)

A

-Lowers activation energy

-Induced fit causes active site (of enzyme) to change shape

-enzyme-substrate complex causes bonds to form/break

20
Q

A dipeptide consists of two amino acids joined by a peptide bond.
Dipeptides may differ in the type of amino acids they contain.
Describe two other ways in which all dipeptides are similar and one way in which they might differ. (3)

A

Similarities
-amine group
-carboxyl group

Difference
-different R-groups

21
Q

Describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction. (3)

A

-Attaches to allosteric site
-Changes shape of the active site
-Active site and substrate no longer complimentary so no e-s complexes form

22
Q

Describe how a peptide bond is formed between 2 amino acids to form dipeptide (2)

A

-Condensation reaction/loss of water
-Between amine and carboxyl

23
Q

Describe how a triglyceride is formed (3)

A

-One glycerol and three fatty acids
-Condensation and removal of 3 water molecules
-Ester bond formed

24
Q

Test for non reducing sugar (3)

A

-Heat with acid and neutralise
-Heat with benedicts
-Red precipitate forms

25
Q

Glycogen and cellulose are both carbohydrates.
Describe two differences between the structure of a cellulose molecule and a glycogen molecule.

A

-Cellulose is made up of b-glucose (monomers) and glycogen is made up of a-glucose (monomers);

-Cellulose molecule has straight chain and glycogen is branched;

26
Q

Describe and explain two features of starch that make it a good storage molecule.

A

-Insoluble in waterso doesn’t affect water potential

-Branched / coiled so makes molecule compact

27
Q

Explain how cellulose molecules are adapted for their function in plant cells.( 3)

A

-Long and straight chain
-Become linked together by many hydrogen bonds to form fibrils;
-Provide strength

bio (24 decks)

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