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A-Level EDUQUAS Biology > Core Concepts: Biomolecules > Flashcards

Core Concepts: Biomolecules Flashcards

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1
Q

What are proteins?

A
  • contain elements C, H,O and N (sometimes S or P)
  • proteins are polymers made up of monomers (amino acids)
  • 20 amino acids, 8 can only be obtained through diet
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2
Q

What are carbohydrates?

A

Carbohydrates are organic compounds, consisting of carbon, hydrogen and oxygen with the general formula C(H2O)n
- monosaccharides, disaccharides and polysaccharides

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3
Q

What are monosaccharides?

A

Small organic molecules that are monomers
- general fromula (CH2O)n
- Named according to the number of carbon atoms…
3C = triose (glyeraldehyde)
5C = pentose (ribose and deoxyribose)
6C = hexose (glucose, fructose and galactose)

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4
Q

Draw alpha and beta glucose

A

Alpha the hydroxyl groups are down, up, down, down
Beta the hydroxyl groups are down, up, down, up
(from carbon 4 to 1)
- 6th carbon is CH2OH

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5
Q

What are the functions of monosaccharides?

A

A source of energy in respiration
- C-H and C-C bonds break to release energy and make ATP
Building blocks for larger molecules
- glucose used to make starch, glycogen and cellulose
Intermediates in reactions
- trioses intermediates in photosynthesis and respiration reactions

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6
Q

What is glucose?

A

Glucose exists as 2 isomers, beta and alpha which form different polymers:

  • starch, a polymer of alpha glucose (composed of straight-chained amylose and branched amylopectin)
  • glycogen, a polymer of alpha (branched structure)
  • cellulose, polymer of beta
  • chitin, polymer of beta with some hydroxyl groups replaced by nitrogen containing acetylamine groups
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7
Q

How does glucose act as a source of energy?

A

Glucose is a main source of energy but it’s soluble in water and therefore increases concentration of cell contents, drawing water in by osmosis
To overcome this glucose is converted into a polysaccharide (starch/glycogen) which…
- is insoluble, has no osmotic effect
- can’t diffuse out the cell
- compact molecule
- carries lots of energy in carbon-carbon/carbon-hydrogen bonds (17kJg^-1)
- glucose can be added and removed easily

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8
Q

What is the polysaccharide cellulose?

A
  • structural polysaccharide, present in cell walls
  • consists of long parallel chains of beta glucose units joined by 1-4 glycosidic bonds but every other unit is rotated 180°
  • H-bonds form between adjacent chains (stability), multiple chains cross-linked form bundles called microfibrils, held in bundles of fibres (strength)
  • cellulose fibres are freely permeable (spaces in between)
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9
Q

What is the polysaccharide chitin?

A
  • structural polysaccharide found in the exoskeletons of insects and in the cell walls of fungi
  • carbon 2 has an acetylamine group replacing the hydroxyl group
  • long chains of beta 1-4 linked glucose monomers, rotated 180° in relation to their neighbour and chains are cross linked by hydrogen bonds forming microfibrils
  • lightweight, strong and waterproof
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10
Q

What are the functions of lipids?

A
  • energy source and storage
  • protection of delicate organs
  • oxidation of triglycerides produces metabolic water
  • biological membranes
  • waterproofing
  • insulation (thermal and electrical)
  • hormones
  • water source
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11
Q

What happens if someone’s diet is high in unsaturated fats?

A
  • liver increases production of HDLs
  • HDL scavenge excess LDLs in the blood and then return them to the liver for disposal
  • A higher ratio of HDLs to LDLs decreases risk of cardiovascular and coronary heart diseases
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12
Q

What are saturated fatty acids?

A
  • fats e.g. lard
  • tend to be found in animals
  • in the hydrocarbon chain all carbon atoms are saturated with hydrogen and all carbons joined by single bonds
  • form straight chains
  • high melting points so are solid at room temperature
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13
Q

What are unsaturated fatty acids?

A
  • oils e.g. olive oils
  • tend to be found in plants
  • in the hydrocarbon chain there is at least one carbon-carbon double bond, not saturated with hydrogen
  • form bent chains with low melting points
  • 1 C=C bond = monosaturated
  • 2+ C=C bond = polysaturated
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14
Q

Why are lipids used instead of carbohydrates as an energy store in seeds and animals?

A

Lipids have a higher yield of energy per gram than carbohydrates

  • lipids = 39 kJg^-1
  • carbohydrates = 17 kJg^-1
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15
Q

Describe the formation of a dipeptide?

A
  • two amino acids are joined by a condensation reaction
  • reaction removes a H2O molecule and forms a peptide bond between the amino group of one amino acid and the carboxyl group of another
  • the reverse of a condensation reaction is hydrolysis which splits a dipeptide by adding a H2O molecule
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16
Q

What is a polypeptide chain?

A

Both ends of a dipeptide can react with another amino acid, building a chain of amino acids, this is a polypeptide chain

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17
Q

What is the primary structure?

A

The sequence of amino acids held together by peptide bonds

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18
Q

What is the secondary structure?

A
  • folding of the primary structure
  • chain coils to form an alpha helix or a beta pleated sheet
  • both structures held together by many hydrogen bonds
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19
Q

What is the tertiary structure?

A
  • further folding of the polypeptide chain to give more complex 3D shapes
  • stabalised by: hydrogen bonds (OH groups), disulphide bonds (S-S, cysteine), ionic bonds (between charged R-groups) and hydrophobic interactions (between non-polar R-groups)
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20
Q

What is the quaternary structure?

A

Proteins that are made up of more than one polypeptide chain

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21
Q

What is a fibrous protein?

A
  • fibrous proteins form long fibres
  • usually insoluble in water
  • generally structural roles (e.g. myosin in muscles and keratin in hair)
  • no prosthetic group
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22
Q

What is an example of a fibrous protein?

A

Collagen - in skin

  • a tropocollagen formed of 3 identical polypeptide chains twisted around each other, forming a triple helix
  • every 3rd amino acid in the chains is glycine
  • chains are linked by hydrogen bonds creating stability
  • molecules cross-link to form covalent bonds creating strength
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23
Q

What is a globular protein?

A
  • fold up into a compact ball like shape
  • more soluble than fibrous proteins
  • metabolic roles (e.g. enzymes)
  • can have a prosthetic group
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24
Q

What is an example of a globular protein?

A

Haemoglobin

  • 4 polypeptide chains (2 alpha and 2 beta)
  • each chain has a haem group (prosthetic group) which contains a Fe2+ ion
  • carries oxygen from the lungs to respiring tissues
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25
Q

Explain why a mistake leading to the insertion of the wrong amino acid during protein synthesis could produce an enzyme that doesn’t function?

A
  • The ‘wrong’ amino acid may not form the same bonds in the tertiary structure as the primary structure has changed
  • therefore folding will give the molecule a different shape and a different active site which won’t be complementary to the substrate
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26
Q

Glucose is transported into cells by carrier proteins in the cell surface membrane. How do carrier molecules specifically recognise glucose?

A

The transport proteins are specific to the thing they transport because of their shape (specific shape bind to the substrate)

27
Q

What is the food test for starch?

A

Add dilute iodine solution to a sample and mix well

If positive there will be a colour change from yellowy-brown to blue-black

28
Q

What are the purposes of proteins?

A
  • enzymes which catalyse reactions
  • carrier proteins transport molecules across membranes
  • antibodies defend against disease
  • structural proteins support cells and tissues
  • hormones transmit information
  • transport proteins (haemoglobin)
  • contractile proteins
29
Q

What is the food test for reducing sugars?

A

Add benedict’s reagent to the sample, mix well and then boil for one minute

If present there will be a colour change from blue to brick red precipitate

30
Q

What is the food test for non-reducing sugar (sucrose)?

A
  • add 1cm^3 of HCl to sample and boil to hydrolyse the sucrose into glucose and fructose
  • neutralise solution with an alkali
  • check solution is neutral/slightly alkaline with pH indicator paper (green)
  • boil for 1 min with benedict’s reagent

if present there will be a colour change from blue to brick-red precipitate

31
Q

What is the food test for proteins?

A

Add biuret reagent to the sample and mix well

If present there will be a colour change from blue to purple precipitate

32
Q

What is the food test for lipids?

A
  • mix absolute ethanol with sample, dissolves any lipids present
  • shake with an equal volume of distilled water
  • dissolved lipids are insoluble in water so they come out of solution and form an emulsion

if present there will be a colour change from colourless to a cloudy white emulsion

33
Q

What is meant by the term organic and inorganic?

A

Organic: molecules that have a high proportion of carbon atoms

Inorganic: a molecule or ion that has no more than one carbon atom

34
Q

What are the most common elements in living organisms?

A

hydrogen, carbon, oxygen and nitrogen

35
Q

What are the roles of magnesium ions (Mg2+)?

A
  • in plants Mg2+ is important component of chlorophyll, therefore essential for photosynthesis (without, chlorosis takes place)
  • in mammals Mg2+ is needed for bones
36
Q

What are the roles of iron ions (Fe2+)?

A

Fe2+ is an important constituent of haemoglobin (prosthetic group)
- without someone will develop anaemia

37
Q

What are the roles of phosphate ions (PO4^3-)?

A

PO4^3- is used for making nucleotide and ATP as well as being a constituent part of phospholipids

38
Q

What are the roles of calcium ions (Ca2+)?

A

Ca2+ is a structural component of bones and teeth in mammals as well as being a component of cell walls in plants

39
Q

How is water a universal solvent?

A

Wate is a dipole molecule (but no overall charge)

  • this allows water molecules to form hydrogen bonds with other H2O molecules (H-bonds are singularly weak but lots makes water molecules hard to separate)
  • other polar molecules and ions are attracted to H2O molecules causing them to dissolved in water
40
Q

Why is water being a universal solvent important in both plants and animals?

A

Plants -> solutes can dissolve in water to be transported in the xylem and phloem vessels

Animals -> solutes can be dissolved to be transported in the blood plasma

41
Q

How is cohesion created in water?

A

individually the H-bonds are weak but because there are many, molecules stick together in a lattice
- this sticking together is called cohesion

42
Q

How is the cohesion of water important to plants?

A

Allows columns of water to be drawn up xylem vessels in plants

43
Q

Why does water have a high specific heat capacity?

A
  • water can absorb a lot of heat energy before the temperature increases
  • H-bonds restrict movement, this restricts an increase of kinetic energy, therefore resists an increase of temperature
  • prevents fluctuations in temperature
44
Q

How is a high specific capacity of water important to plants and animals?

A
  • keeps aquatic habitats stable, organisms don’t have to adapt to extremes of temperatures
  • enables enzymes to work efficiently
45
Q

What is meant by water having a high latent heat of vaporisation and what is the importance of this for animals?

A

Lots of heat energy is needed for water to change state from a liquid to a gas (vapour)

Important in temperature controls:

  • excess heat used to vaporise water on the skin (sweat)
  • as water evaporates the body cools
46
Q

Why is ice less dense than liquid water?

A
  • In ice the hydrogen bonds hold the molecules further apart than in liquid water (more space between the molecules)
  • Water has a maximum density at 4°C
  • When water freezes volume increases but no mass, therefore the density will increase
47
Q

How is the density of ice important to plants and animals?

A

ice floats on water forming an insulating layer on the surface of the water, prevents large bodies of water losing heat/freezings, organisms below will survive

48
Q

How does water play a role as a metabolite?

A
  • Used in many biochemical reactions as a reactant

- hydrolysis (water splitting molecule) and condensation (water is a product)

49
Q

Why is a high surface tension of water important?

A

Cohesion between water molecules creates surface tension

- body of an inset can be supported (e.g. pond skater)

50
Q

What is a phospholipid?

A

A glycerol, 2 fatty acids and a phosphate group

- has 2 hydrophobic tails and a hydrophilic head

51
Q

Describe the parts of a lipid molecule in terms of its interactions with water

A
  • glycerol is hydrophilic because of its polar hydroxyl groups
  • hydrocarbon chains of fatty acids are hydrophobic (non-polar) whilst the (polar) carboxyl group is hydrophilic (fatty acids are hydrophobic)
  • hydrophilic groups are used in forming the ester bond of triglycerides hence the insolubility in water
52
Q

What are the 2 differences between phospholipids and triglycerides?

A
  1. phospholipids have a charged phosphate group, triglycerides don’t
  2. phospholipids have 2 fatty acids instead of 3
53
Q

What are the 2 main causes of heart disease?

A
  1. fatty deposits in coronary arteries (atheroma)

2. high blood pressure (hypertension)

54
Q

What are the factors which contribute to heart disease?

A
  • diet high in saturated fats
  • smoking
  • lack of exercise
  • age
55
Q

What is the basic structure of an amino acid?

A 
Amino group -NH2 (N-terminal)
Central carbon
Hydrogen atom
R group (variant)
Carboxyl group -COOH (C-terminal)
56
Q

What are the monosaccharide combinations for 3 disaccharides?

A

glucose + glucose = maltose
glucose + fructose = sucrose
glucose + galactose = lactose

57
Q

Where is maltose, sucrose and lactose found?

A

maltose -> germinating seeds
sucrose -> transport in phloem of flowering plants
lactose -> mammalian milk

58
Q

Why is water being transparent important?

A

Allows for light to pass through so aquatic plants can photosynthesise effectively

59
Q

What is meant by the terms ‘monomer’ and ‘polymer’?

A

Monomer - single repeating unit of polymer

Polymer - a large molecule comprising of repeated units (monomers) bonded together

60
Q

Describe glycogen as a polysaccharide?

A
  • main storage product in animals of alpha glucose
  • branched and chain polymer
  • more compact than starch
  • 1-4 and 1-6 glycosidic bonds
  • glycogen is stored as glycogen granules in the liver and muscle cells
61
Q

Describe starch as a polysaccharide?

A
  • main storage of glucose in plants
  • found in high concentrations in seeds and potato tubers
  • made of alpha glucose and bonds in two different ways…
    1. amylose a linear, unbranched molecule with 1-4 glycosidic bonds, forms a chain coiling into a helix
    2. amylopectin a branched polymer with 1-4 glycosidic bonds cross-linked with 1-6 glycosidic bonds of alpha glucose
62
Q

What are the elements that make up lipids?

A

carbon, hydrogen, oxygen and phosphorus (as phosphate in phospholipids)

63
Q

What is a triglyceride and draw the reaction?

A
  • formed by the condensation reaction of one glycerol molecule and 3 fatty acids
  • 3 ester bonds are formed and 3 H2O molecules formed
64
Q

What happens if someone’s diet is high in saturated fats?

A
  • liver increase production of LDLs (low-density lipoproteins)
  • atheroma is deposited by LDLs in coronary arteries which restricts blood flow and therefore reduces the amount of oxygen being delivered to the heart muscle
  • can result in angina and if the whole vessel is blocked a myocardial infarction

A-Level EDUQUAS Biology (24 decks)

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