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AQA AS Biology > Section 1 - Unit 1: Biological Molecules > Flashcards

Section 1 - Unit 1: Biological Molecules Flashcards

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1
Q

Describe how R groups can interact to determine the tertiary structure of a protein (4 marks)

A
  • some R groups, attract / repel
  • disulfide bridges form between cysteine atoms
  • hydrogen bonds and ionic bonds form
  • the hydrophilic R groups are on the outside of molecule
  • the hydrophobic R groups are on the inside of molecule
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2
Q

Explain how companion cells are adapted for the transport of sugars between cells (2 marks)

A

Mitochondria are present to release energy for active transport
OR
Ribosomes produce proteins needed for transport

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3
Q

Describe the structure of proteins (6 marks)

A
  • Polymer of amino acids (1) joined by peptide bonds (1) due to a condensation reaction
  • Primary structure is order of amino acids
  • Secondary structure is the folding of polypeptide chain due to hydrogen bonding
  • Tertiary structure is 3-D folding due to hydrogen bonding and ionic / disulfide bonds
  • Quaternary structure is two or more polypeptide chains with both protein and non-protein groups
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4
Q

Give four properties of water that are important in biology and state the importance of each property (8 marks)

A
  • POLAR so dissolves charge particles/ acts as a solvent
  • LARGE COHESIVE FORCES so provides surface tension/ prevents columns of water breaking
  • HIGH SPECIFIC HEAT CAPACITY so reduces fluctuations in body temperature
  • HIGH LATENT HEAT OF EVAPORATION so keeps the body cool
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5
Q

Explain why a column of water pulled through a xylem vessel does not break (3 marks)

A

Water molecules are polar (1) so hydrogen bonds form between each molecule of water (1) and the large cohesive forces prevent breakage

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6
Q

Explain the effect on a plant caused by the evaporation of water from its leaves (2 marks)

A
  • The plant’s heat is used to evaporate water mean that heat is transferred away from the plant (1)
  • This cools the plant (1)
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7
Q

Explain why organisms that live on land experience greater ranges of temperature than organisms that live in water (2 marks)

A
  • Water has a very high specific heat capacity (1) meaning that more energy is needed to change the temperature (1) compared to air which has a lower specific heat capacity
  • This means that the temperature can range very easily on land whereas it can’t underwater
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8
Q

Explain why water becomes lighter as it expands to become ice (2 marks)

A
  • Density = Mass/Volume (1)

- Ice has the same mass as water but a larger volume (1), meaning that the density decreases and it becomes lighter

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9
Q

Explain why water freezing to become ice is an advantage (3 marks)

A
  • Ice is colder than water and floats on top, providing a habitat to some animals (1)
  • It also acts as a protection, preventing the water below from freezing (1)
  • It acts as a form of insulation for animals and protects them from the cold (1)
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10
Q

Explain why water is considered so important for life to occur (6 marks)

A
  • Water isn’t easily compressed so it provides a good structure and support for the bodies of some organisms (1)
  • All cells contain cytoplasm and water is a major component of cytoplasm so without water, organisms could not have been formed (1)
  • For organisms to be alive, metabolic reactions have to take place and water is a major component of metabolism (1) since it is both a good solvent (1) and good reactant (1)
  • Water is also important in stabilising internal and external temperatures for organisms to survive (1)
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11
Q

Describe the structure of a cellulose molecule and explain how cellulose is adapted for its function in cells (6 marks)

A
  • Cellulose is made from β-glucose
  • And is joined by a condensation reaction to form a glycosidic bond
  • 1,4 link where every alternate glucose molecule in cellulose is inverted
  • Hydrogen bonds link chains to form microfibrils
  • And this makes the cell walls strong enough to resist osmotic pressure
  • The bonds are difficult to break and this resists enzyme activity
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12
Q

Why is water a good solvent (1 mark)

A
  • Dipolar molecule so polar molecules can bind to it to form minerals and nutrients
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13
Q

Give examples of water as a metabolite (3 marks)

A
  • Plasma Membranes
  • Cytoplasms of cells
  • Hydrolysis reactions
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14
Q

Explain why water has a high specific heat capacity (2 marks)

A
  • Stable hydrogen bonds between the molecules

- So a lot of energy is needed to overcome/break these bonds

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15
Q

State three differences between glycogen and collagen (3 marks)

A
  • Branched vs unbranched
  • Carbohydrate vs protein
  • Non-helical vs helical
  • Glycosidic bonds vs peptide bonds
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16
Q

Suggest why it might be better for people to let cattle feed on the trees and fallen seed pods and then obtain their nutrition (protein) from the cattle (3 marks) {past exam questions}

A
  • humans only eat the seeds so won’t gain their nutrition from the seed pods
  • the seeds humans eat may be deficient in some of the proteins
  • cattle are probably better at digesting the seed pods than humans
17
Q

Describe the molecular structure of glycogen (6 marks)

A
  • Polymer (1) composed of α-glucose (1)
  • Joined by 1,4 links (1) and 1,6 links where branches attach (1)
  • Glycosidic Bonds (1)
  • Compact, i.e. short chains but highly branched (1)
18
Q

Explain why cholesterol must be carried in the blood by proteins while glucose does not need any transport protein (2 marks)

A
  • Cholesterol is insoluble in water since it is hydrophobic

- Glucose is soluble in water since it is hydrophilic

19
Q

Differences between fibrous and globular proteins (4 marks)

A
  • long and straight vs round
  • insoluble vs soluble
  • strong intermolecular forces vs weak intermolecular forces
  • mainly structural functions vs metabolic functions
20
Q

Explain how the structure of collagen contributes to its strength (3 marks)

A
  • Amino acids form a tightly wrapped coil
  • Held together by hydrogen bonds
  • Molecules form fibrils
21
Q

State the major difference between chitin and other types of polysaccharides (1 mark)

A

Chitin is nitrogenous

22
Q

State three functions of lipids in animals/plants (3 marks)

A
  • Storage of energy
  • Structural component of hormones
  • Act as signalling molecules
23
Q

Insulin is a peptide hormone produced in the pancreas. People who suffer from type 1 diabetes are often given insulin as a treatment. Why are patients given insulin via injection into the blood rather than by taking a pill? (6 marks)

A

Insulin is a protein.

  • If insulin were eaten as a pill it would be broken down by protease enzymes in the stomach or the intestine.
  • If some insulin managed to escape digestion it would likely be denatured by the low pH of the stomach.
  • If insulin survived both these things, it would not be small enough to be absorbed in the small intestine into the bloodstream and, therefore, would not reach the body tissues.
24
Q

Why does ice float on water?

A

The lattice structure of ice created through hydrogen bonding makes ice less dense than the freely flowing molecules of liquid water

25
Q

Explain how glycogen act as an energy source (2 marks)

A
  • Glycogen can be hydrolysed to form glucose

- The glucose could then be used to release energy through the process of respiration

26
Q

Where is the linkage made that combines two amino acids?

A
  • Between the six carbon of both amino acids
27
Q

What causes the changes in protein structure through the three or four levels of structure?

A
  • The primary chain forms a secondary alpha helix and beta pleated sheets which fold onto each other forming the tertiary structure
28
Q

What structural level of proteins is functional? Why? (2 marks)

A
  • The tertiary structure

- Since it possesses the geometric shape, showing the necessary loops and bends

29
Q

Explain how the formation of an enzyme-substrate complex increases the rate of reaction (2 marks)

A
  • Reduces activation energy

- Due to bending bonds

30
Q

Compare and contrast the structure and properties of triglycerides and phospholipids (5 marks)

A
  • Both contain ester bonds
  • Both contain glycerol
  • Fatty acids on both may be saturated or
    unsaturated
  • Both are insoluble in water
  • Both contain C, H and O but phospholipids also contain P
  • Triglyceride has three fatty acids and
    phospholipid has two fatty acids plus phosphate group
  • Triglycerides are hydrophobic and
    phospholipids have hydrophilic and
    hydrophobic region
  • Phospholipids form bilayer in water but
    triglycerides don’t
31
Q

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein (4 marks)

A
  • Glucose and galactose
  • Condensation reaction
  • Glycosidic bond
  • Added to polypeptide in Golgi
32
Q

Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers. Give two named examples of polymers and their associated monomers to illustrate your answer (5 marks)

A
  • A condensation reaction joins monomers together and forms a (chemical) bond and releases water
  • A hydrolysis reaction breaks a (chemical) bond between monomers and uses water

For example:

  • Triglycerides are made of 3 fatty acids and 1 glycerol
  • Ester Bonds
  • Galactose is hydrolysed into lactose and alpha glucose
  • Glycosidic bonds
33
Q

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

A
  • A metabolite in condensation / hydrolysis
  • A solvent so metabolic reactions can occur
  • High 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)
  • Cohesion (between water molecules) so produces surface tension supporting (small) organisms
34
Q

Explain how formation of an enzyme substrate complex increases the rate of reaction (2 marks)

A
  • Reduces activation energy

- Due to bending bonds

AQA AS Biology (14 decks)

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