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AQA A Level Biology > BIOLOGICAL MOLECULES > Flashcards

BIOLOGICAL MOLECULES Flashcards

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1
Q

What is a monomer?

A

Small molecules which join through condensation reactions to form larger molecules (polymers)

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2
Q

What is a polymer?

A

Large molecules made from many smaller molecules joined together (monomers)

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3
Q

What is a condensation reaction?

A

Chemical bond forms between 2 molecules, water is lost

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4
Q

What is a hydrolysis reaction?

A

Water is used to break chemical bond between 2 molecules

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5
Q

What is glucose & types of glucose?

A

Hexose sugar (6 carbon atoms). Two types: alpha and beta - isomers (same molecular formula, different atom structure)

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6
Q

What are the disaccharides?

A

Maltose: glucose + glucose
Sucrose: glucose + fructose
Lactose: glucose + galactose

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7
Q

Benedict’s test for reducing sugars?

A
  1. Add equal volume of Benedict’s reagent to sample
  2. Heat in water bath for 5 mins
  3. Positive result = colour change from blue to brick red
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8
Q

Benedict’s test for non-reducing sugars?

A
  1. Hydrolyse sample by adding hydrochloric acid
  2. Heat in water bath
  3. Neutralise with sodium hydrogen carbonate
  4. Repeat process of Benedict’s test
  5. Positive result = colour change from blue to brick red
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9
Q

What is glycogen?

A

A highly branched polysaccharide with shorter chains. Energy storage in animals (alpha-glucose).

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10
Q

What is glycogen’s structure relating to function?

A

Branched: many terminal ends for enzymes to act on, can be rapidly hydrolysed to release glucose for respiration to provide energy
Insoluble: doesn’t affect water potential & doesn’t diffuse out of cells
Compact: fit more into smaller spaces

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11
Q

What is cellulose?

A 
Provides strength & structural support to plant cell walls (beta-glucose).
Doesn't form coils, instead straight unbranched chains.
Cross linkages (hydrogen bonds) between chains
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12
Q

What is cellulose’s structure relating to function?

A

Hydrogen bonds high in numbers: strength

Hydrogen bonds link parallel strands to form strong fibres called microfibrils: provide structural support to cell

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13
Q

What is starch?

A

Energy storage in plants (alpha-glucose).
Mixture of 2 polysaccharides: amylose & amylopectin
Amylose - long, unbranched, gives coiled structure (compact & good for storage)
Amylopectin - long, branched, side branches give enzymes easy access so glucose is released quickly

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14
Q

What is starch’s structure relating to function?

A

Insoluble: water potential not affected (osmosis)
Large & insoluble: doesn’t diffuse out of cell
Helical & compact: can fit more in smaller space for storage
Branched: many terminal ends for enzymes to act on + quick release of monomers

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15
Q

What is the test for starch?

A

Iodine test:

  1. Add iodine solution to food sample
  2. Positive result: colour change from orange to blue-black
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16
Q

What are triglycerides?

A

Formed by condensation reaction between 1 molecule of glycerol and 3 fatty acids, form ester bonds

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17
Q

Difference between saturated and unsaturated fatty acids?

A

Saturated:
- contain only single bonds
- straight chain molecules, many contact points
- higher melting point = solid at room temp
- found in animal fats
Unsaturated:
- contain C=C double bonds
- ‘kinked’ molecules, fewer contact points
- lower melting point = liquid at room temp
- found in plant oils

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18
Q

What are phospholipids?

A 
Found in cell membranes
Similar to triglycerides, except one fatty acid is replaced with a phosphate
Phosphate group (head) = hydrophillic
Fatty acid tails = hydrophobic
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19
Q

What is triglycerides’ structure related to function?

A

Energy storage molecules:

  • high energy:mass ratio = good energy storage
  • insoluble hydrocarbon chain = no effect on water potential
  • slow conductor of heat = thermal insulation
  • less dense than water
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20
Q

What are phospholipid’s structure related to function?

A

Make up bilayer of cell membranes:

  • hydrophillic head & hydrophobic tails = form double layer
  • centre of bilayer = hydrophobic, water-soluble substances cannot pass
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21
Q

What is the test for lipids?

A

Emulsion test:

  1. Add ethanol to food sample
  2. Shake it
  3. Add water
  4. Shake it
  5. Positive result: cloudy white emulsion
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22
Q

Structure of amino acids?

A

Carboxyl group: (-COOH)
Amine group: (-NH2)
R group/variable group
Linked together by condensation reactions to form polypeptides
Bonds between amino acids = peptide bonds

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23
Q

Primary structure of proteins?

A

Sequence of amino acids in a polypeptide chain joined by peptide bonds

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24
Q

Secondary structure of proteins?

A

Hydrogen bonds form between amino acids making chain coil into alpha helix or fold into beta pleated sheet

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25
Q

Tertiary structure of proteins?

A

Chain is coiled / folded further. Hydrogen & ionic bonds form. Disulfide bridges form when 2 cysteine come close.

26
Q

Quaternary structure of proteins?

A

Several polypeptide chains held together joined by hydrogen bonds, final 3D structure

27
Q

Functions of proteins?

A

Enzymes: spherical due to tight folding. Soluble & roles in metabolism
Antibodies: involved in immune response
Transport: eg channel protein, present in cell membranes. Transport molecules & ions across membranes.
Structural: physically strong, consist of long polypeptide chains parallel to each other with cross-links between them.

28
Q

What is the test for proteins?

A

Biuret test:
(if solid, crush then add water to make liquid)
1. Add Biuret Reagent to food sample
2. Add distilled water
3. Shake it
4. Positive result: colour changes to lilac/pink/purple

29
Q

What are enzymes?

A

Globular protein which speed up chemical reactions by acting as biological catalysts.

  • Catalyse metabolic reactions & can affect structures/functions of organelles
  • Can be intracellular (inside cell) or extracellular (outside cell)
  • Highly specific due to tertiary structure & active site’s specific shape
  • Lowers activation energy to speed up rate of reaction without being changed itself
  • When substrate binds to active site = forms enzyme-substrate complex
30
Q

What is the lock and key theory?

A

Substrate fits into enzyme’s active site without changing either’s shape

31
Q

What is the induced fit model?

A

As substrate binds, the active site slightly alters it’s shape

32
Q

What is the tertiary structure of an enzyme?

A

Very specific & can only catalyse one reaction - only one complementary substrate
Active site’s shape is determined by tertiary structure of enzyme

33
Q

How does temperature affect enzyme activity?

A
  • Rise in temp = enzyme molecules vibrate more
  • If temp goes above certain level, vibration breaks bonds that hold enzymes in shape, so active site changes & substrate no longer fits (enzyme denatures)
34
Q

How does pH affect enzyme activity?

A
  • Above & below optimum pH (humans=7), the H+ and OH- ions found in acids & alkalis mess up ionic & hydrogen bonds that hold the tertiary structure of enzyme in place
  • Active site’s shape changes, enzyme denatures
35
Q

How does enzyme concentration affect rate of reaction?

A
  • More enzyme molecules = more likely collisions with substrate
  • Increases rate of reaction
36
Q

How does substrate concentration affect rate of reaction?

A
  • Higher substrate concentration = faster reaction
  • More substrate molecules = more likely collisions up until ‘saturation’ where all active sites are full
  • Substrate concentration decreases with time so rate of reaction will too
37
Q

What is competitive inhibition?

A
  • Competitive inhibitors have SIMILAR shape to substrate
  • Compete with substrate molecules to bind to active site (no reaction occurs)
  • Block active site so substrate cannot bind
  • High concentration of inhibitor = takes up most active sites so no reactions
  • High concentration of substrate = chances of binding to active site increases, more likely reactions
38
Q

How do you calculate rate of reaction from a graph?

A

Initial rate of reaction - rate of reaction at start of reaction
1. Draw tangent to curve at time = 0, estimate where curve would continue if carried on below zero
2. Calculate gradient of tangent (initial rate of reaction)
Gradient = change in y / change in x

39
Q

What is the structure of DNA?

A

Type of nucleic acid, polymer of nucleotides

  • Contains deoxyribose pentose sugar
  • 4 nitrogen-containing organic bases: Adenine & Thymine, Cytosine & Guanine
  • Contains phosphate group
  • Double stranded, double helix
  • Sugar-phosphate backbone
40
Q

What is the structure of RNA?

A

Type of nucleic acid, polymer of nucleotides

  • Contains ribose sugar
  • Has phosphate group and 1 of 4 bases
  • Uracil replaces Thymine as a base
  • Made from single polypeptide chain, much shorter than DNA
41
Q

How do nucleotides join to form polynucleotides?

A

Nucleotides join via condensation reaction between phosphate group of one and pentose sugar of another
Forms phosphodiester bond
Chain of sugars & phosphates = sugar phosphate backbone

42
Q

What is the hydrolysis of ATP?

A

ATP + water -> ADP + phosphate (Pi) + energy

reaction catalysed by the enzyme ATP hydrolase

43
Q

What is the condensation of ATP?

A

ADP + phosphate (Pi) -> ATP + water

44
Q

What are the different types of RNA?

A

mRNA: transfers genetic information from nucleus to ribosomes
tRNA: involved in protein synthesis (carries amino acids to mRNA)
rRNA: ribosomes are made of this type of RNA

45
Q

What are purines and pyrimidines?

A

Purines: Adenine and Guanine (double ringed structure)
Pyrimidines: Cytosine and Thymine (single ringed structure)

46
Q

What are the steps of semi-conservative replication?

A
  1. DNA helicase separates two strands of DNA by breaking hydrogen bonds, exposing the nucleotides
  2. DNA helicase completes separation of the strands, nucleotides actively bind to complementary bases on template strands
  3. Once DNA nucleotides are bound, they’re joined together by DNA polymerase which makes phosphodiester bonds. Polymerase adds nucleotides in 5’ to 3’ direction
  4. Hydrogen bonds form between the bases on the original and new strands
  5. All nucleotides are joined to form a complete polypeptide chain
47
Q

What is the structure of water?

A

2 atoms of hydrogen covalently bonded to 1 molecule of oxygen
Polar = electrons not evenly distributed across molecule (hydrogen’s slightly positive, oxygen’s slightly negative), attraction between these charges forms hydrogen bonds

48
Q

What are the properties of water?

A

Metabolite:
- metabolic reactions involve condensation or hydrolysis reactions
- hydrolysis requires water, condensation releases water
High Latent Heat of Vaporisation:
- lots of energy used when water evaporates (takes lots of energy to break hydrogen bonds between water molecules)
- organisms use water loss through evaporation to cool down
High Specific Heat Capacity:
- water takes lots of energy to heat up (hydrogen bonds between molecules absorb lots of energy)
- means water doesn’t have rapid temp changes, making a good habitat & helps maintain constant internal body temp
Good Solvent:
- ionic substance = 1 positively charged molecule & 1 negatively charged molecule
- positive end of water attracts negative end of ion & vice versa, ion gets surrounded by water & dissolves
Strong Cohesion Between Water Molecules:
- cohesion = attraction between molecules of same type
- helps water flow, good for transporting substances
- means water has high surface tension with air (sweat droplets)

49
Q

What is ATP?

A

A modified form of a nucleotide, made from adenine, ribose sugar and 3 phosphate groups

50
Q

How is ATP an immediate source of energy in a cell?

A
  • Plant & animal cells release energy from glucose in respiration
  • Energy released from glucose is used to make ATP
  • ATP diffuses to part of cell needing energy
  • Energy in ATP is stored in high energy bonds between phosphate groups, and released via hydrolysis reactions
51
Q

How is ATP quickly made and used?

A
  • When energy’s needed by a cell, ATP breaks down into ADP and Pi (inorganic phosphate) through hydrolysis
  • Phosphate bond is broken, energy is released, reaction is catalysed by enzyme ATP hydrolase
  • Released Pi can be added to another compound, often making it more reactive
52
Q

How is ATP resynthesised?

A

In a condensation reaction between ADP and Pi. Happens during respiration and photosynthesis, catalysed by enzyme ATP synthase.

53
Q

What are the functions of ATP?

A

Metabolic processes:
- provides energy to build macromolecules from their basic units
Movement:
- provides energy for muscle contraction, energy is needed for the filaments to slide over each other
Active transport:
- provides energy to change shape of carrier proteins in plasma membranes, so molecules can be transported against their concentration gradient
Activation of molecules:
- the inorganic phosphate released can phosphorylate other compounds, lowering the activation energy
Secretion:
- used to form lysosomes (enzyme inside cells to degrade molecules)

54
Q

What is an ion?

A

Atom / group of atoms with an electric charge
Ion with positive charge = cation
Ion with negative charge = anion
Inorganic ion does not contain carbon
Can be in solution, cytoplasm of cells & in bodily fluids of organisms

55
Q

Why are iron ions an important part of haemoglobin?

A
  • Haemoglobin: large protein, carries oxygen around body in red blood cells, iron ion in centre of each 4 polypeptide chain
  • Iron ion binds to oxygen in haemoglobin, once bound iron Fe2+ ion becomes Fe3+ ion until oxygen is released
56
Q

How do hydrogen ions determine pH?

A
  • pH is calculated based on concentration of hydrogen ions in environment
  • The more H+ present, the lower the pH (and more acidic the environment)
  • Enzyme-controlled reactions are all affected by pH
57
Q

How do sodium ions help transport glucose & amino acids?

A
  • Molecule of glucose / amino acid can be transported into cell across cell-surface membrane alongside sodium ions via co-transport
58
Q

How are phosphate ions an essential component of ATP & DNA?

A
  • Phosphate group = when phosphate ion is attached to another molecule
  • DNA, RNA & ATP are all containing phosphate groups
  • Bonds between phosphate groups store energy in ATP
  • Phosphate groups in DNA & RNA allow nucleotides to join up to form polynucleotides
59
Q

Structure and function of mRNA?

A
  • Single stranded nucleotide chain made up from the complementary bases to the DNA strand it is made from
  • Carries genetic code from DNA to ribosomes, where it is used to make a protein during translation
60
Q

Structure and function of tRNA?

A
  • Single polynucleotide strand folded into clover shape, hydrogen bonds between specific base pairs hold molecule in this shape
  • Carries amino acids used to make proteins, to the ribosomes
  • Has 3 bases at 1 end called anticodon and an amino acid at the other

AQA A Level Biology (9 decks)

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