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A level Biology > Biological molecules ( Core concepts ) > Flashcards

Biological molecules ( Core concepts ) Flashcards

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1
Q

Atom definition

A

A basic unit of matter that consists of a dense, central nucleus surrounded by a
cloud of negatively charged electrons.

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2
Q

Molecule definition

A

An electrically neutral group of at least two atoms in a definite arrangement held
together by very strong (covalent) bonds

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3
Q

Compound definition

A

A pure chemical substance consisting of two or more different chemical elements
that can be separated into simpler substances by chemical reactions.

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4
Q

Element definition

A

A pure chemical substance consisting of one type of atom distinguished by its
atomic number, which is the number of protons in its nucleus

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5
Q

Ion definition

A

A charged particle formed by the loss or gain of one or more electrons

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6
Q

Organic compound definition

A

Any member of a large class of chemical compounds whose molecules contain
carbon except for the oxides e.g. carbon dioxide.

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7
Q

Inorganic compound definition

A

Are considered to be of a mineral, not biological origin

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8
Q

What are the 4 most common elements in living organisms ?

A

Hydrogen, Carbon, Oxygen and Nitrogen

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9
Q

Name the 4 key inorganic ions in living organisms

A

Magnesium, Iron, Calcium and Nitrate ions

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10
Q

Role of Mg2+ in plants

A

Needed to produce chlorophyll / component of chlorophyll

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11
Q

Role of Fe2+ in animals

A

Component of haemoglobin and is involved in the transport of oxygen

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12
Q

Role of Po43- ( phosphate ) in living organisms

A

Component of nucleic acids ( ATP, ADP, DNA, RNA ) and phospholides

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13
Q

Role of Ca2+ in living organisms

A

Strengthens tissues, bones and teeth in animals and cell walls in plants

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14
Q

Why is water essential ?

A

All reactions of life rely on water and key elements are found in aqueous solution.

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15
Q

6 Key water properties

A

Polar molecule - solvent, metabolite, strong cohesion between molecules, high specific heat capacity, high latent heat of vaporisation, density

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16
Q

Explanation and importance of water as a polar molecule

A

Oxygen atom attract electrons more strongly so have a negative charge. Hydrogen atoms have a partial positive charge. Due to polarity, water molecules attract each other by forming hydrogen bonds. Polarity helps charged particles dissolve in water. Water is a solvent for many biological molecules and is necessary for many biochemical reactions.

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17
Q

Explanation and importance of water as a metabolite

A

Water is a metabolite in chemical reactions. It is a reactant in photosynthesis and hydrolysis. It is a product in aerobic respiration and condensation reactions. Condensation reactions form chemical bonds, hydrolysis reactions break chemical bonds. Water provides support and buoyancy.

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18
Q

Explanation and importance of strong cohesion between water molecules.

A

Water molecules show a strong attraction to one another due to hydrogen bonding and attract to other polar molecules. As a result of strong cohesion, the surface tension at the water air boundary is high. This trait enables effective transport of water in tube like transport cells to parts of organisms ( eg xylem vessels in plants )

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19
Q

Explanation and importance of water’s high specific heat capacity

A

A lot of energy is required to warm water up ( can absorb large amounts of heat before a significant temperature change ). Water acts as a temperature buffer and minimises temperature fluctuations in living organisms to help maintain appropriate enzyme activity.

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20
Q

Explanation and importance of water’s high latent heat of vaporisation

A

Water absorbs large amounts of heat energy whilst changing from water to vapour. Large energy needed to break hydrogen bonds. Evaporation of water provides cooling effect with little water loss. Organisms use process to cool down ( sweating ). Plants use process in hot environments to prevent enzyme damage.

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21
Q

Explanation and importance of water’s density compared to ice

A

When water freezes it expands and its density decreases. Ice is less dense than water so it floats of top. In aquatic environments, ice forms an insulatory layer and prevents water column from freezing.

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22
Q

Describe hydrogen bonding between water molecules

A

Weak intermolecular forces of attraction form between a lone pair on a negative oxygen atom and a positive hydrogen atom on an adjacent molecule.

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23
Q

Test for Reducing Sugar ( eg glucose, fructose, maltose )

A

Add 2cm3 Benedict’s solution to an equal
amount of the test sample, heat over a
water bath. Blue to brick red precipitate.

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24
Q

Test for Non Reducing Sugar ( eg sucrose )

A
  1. Boil test sample with HCl (to break
    the glycosidic bonds).
  2. Neutralise with NaHCO3
    /alkali
    (otherwise the HCl would react with
    the Benedict’s solution).
  3. Add Benedict’s solution to the test
    sample, heat over a water bath.
    Blue to brick red precipitate
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25
Q

Test for starch

A

Add a few drops of Iodine solution to test sample. Orange/ brown to blue/black

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26
Q

Test for lipids

A
  1. Shake some of the test sample with
    about 4cm3 of ethanol.
  2. Decant the liquid into a test tube of
    water, leaving any undissolved
    substances behind.
    Clear to formation of white cloudy emulsion
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27
Q

Test for proteins

A

Add a few drops of Biuret reagent to
the test sample. Blue to lilac/purple precipitate

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28
Q

Test for cellulose

A

Add a few drops of Schultze’s solution
to the test sample. Yellow to purple.

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29
Q

Monomers vs Polymers

A

Monomers = the building blocks of life, monomers are small units that make up larger molecules.
Polymers = Large, complex molecules made up of many monomers joined together.

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30
Q

Carbohydrates, proteins and nucleic acids : monomers and polymers

A

Carbohydrates : monomer = monosaccharides, polymer = polysaccharides
Proteins : monomer = amino acids, polymer = polypeptides
Nucleic acids : monomer = nucleotide, polymer = polynucleotides

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31
Q

Condensation reactions vs Hydrolysis reactions

A

Condensation :
small molecules combine to form larger molecules, a new covalent bond is formed and a water molecule is removed.
Hydrolysis :
large molecules are broken down into smaller molecules, a covalent bond is broken and a water molecule is added.

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32
Q

Carbohydrates general formula

A

C(H2O)n

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33
Q

3 main types of carbohydrates

A

Carbohydrates are molecules which consist only of carbon, hydrogen and oxygen and they are long chains of sugar units called saccharides. There are three types of saccharides -
monosaccharides, disaccharides and polysaccharides.

34
Q

What are the names for sugars with 3,5 and 6 carbons ?

A

Triose ( glyceraldehyde )
Pentose ( ribose, deoxyribose )
Hexose ( alpha and beta glucose, fructose, galactose )

35
Q

How is a disaccharide formed ?

A

Two monosaccharides join together by a glycosydic bond using a condensation reaction.

36
Q

Name the three hexose disaccharides and how they are formed

A

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

37
Q

Main functions of carbohydrates in humans

A

energy source and energy stores
instant energy source = glucose, transportable energy source = glycogen in the liver

38
Q

What are polysaccharides ?

A

Polysaccharides are polymers made up of many glucose molecules linked together by condensation reactions

39
Q

Describe the structure of starch

A

a polymer of alpha glucose. Composed of straight-chain amylose containing 1-4 glycosidic bonds and branched amylopectin containing 1-4 and 1-6 glycosidic bonds. used for storage in plant cells.

40
Q

Describe the structure of cellulose

A

a polymer of beta glucose, straight chains with 1-4 glycosidic bonds, every other glucose rotated 180 degrees. H bonds holding together chains to form microfibrils, making it strong and support the plant cell - preventing it from bursting when the plant cell becomes turgid. No cell rupture. Forms cell wall in plants - Strong, waterproof and lightweight.

41
Q

Describe the structure of chitin

A

a polymer of ? glucose with acetylamine groups, straight chains with 1-4 glycosidic bonds, every other glucose rotated 180 degrees. H bonds holding together chains to form microfibrils, making it strong. Form exoskeletons of insects and found in fungi cell walls. Strong, waterproof and lightweight.

42
Q

Describe the structure of glycogen

A

a polymer of alpha glucose- branched structure containing 1-4 and 1-6 glycosidic bonds. Coiled and branched shape. Used for storage in animal cells.

43
Q

How are starch and glycogen well adapted as storage polysaccharides ?

A

Glucose can be added or removed easily
They are coiled / branched and therefore compact
They have no osmotic effect in cells because they are insoluble.
They have a high energy content because of the C-H bonds.

44
Q

What is important in maintaining the shape of biological molecules ?

A

Hydrogen bonding.

45
Q

Difference between alpha and beta glucose

A

Alpha : the OH group is below Carbon 1
Beta : the OH group is above Carbon 1

46
Q

What elements make up lipid molecules ?

A

Carbon, Hydrogen and Oxygen plus phosphurus as phophate in phospholides.

47
Q

What, in lipids, depends on the melting points of the lipid ?

A

Oils ( liquid ) or fats ( solid )

48
Q

Why are lipids soluble in organic solvents but not water ?

A

Water is a polar molecule which dissolves polar molecules ( such as glucose, amino acids and globular proteins ) and ions. Lipids have fatty acid tails which are non polar and hydrophobic, so water cannot form hydrogen bonds with them and cannot dissolve them.

49
Q

State the functions of lipids

A

Energy source and storage
Protection of delicate organs
Insulation
Oxidation of triglycerides
Waterproofing
Membranes
Hormones

50
Q

Explain how a triglyceride is formed

A

One molecule of glucose joins together with three fatty acid molecules to form a triglyceride molecule, in a condensation polymerisation reaction. In this reaction, a water molecule is removed and an ester bond is formed.

51
Q

How does the structure of triglycerides relate to the functions ?

A

High energy to mass ratio - energy storage, high calorific value from oxidation
Insoluble hydrogen chain - no effect on water potential of cells, used for waterproofing
Slow conductor of heat - thermal insulation
Less dense than water - buoyancy of aquatic animals

52
Q

What is a saturated fatty acid ?

A

There are no C=C double bonds so all carbon atoms are linked to the max possible number of hydrogen atoms. Solid at room temp.

53
Q

What is an unsaturated fatty acid ?

A

There is at least one C=C double bond in the chain, so they don’t have the maximum theoretic amount of hydrogen attached.
Monounsaturated = one C=C double bond, polyunsaturated = two or more C=C double bond.

54
Q

Why are lipids used, rather than carbohydrates, as an energy store in seeds and animals ?

A

Because lipids have a higher yield of energy per gram than carbohydrates and proteins, i.e. about 39kJg-1 compared with about 17kJg-1

55
Q

What are the products of lipid hydrolysis ?

A

Fatty acids and glycerol

56
Q

What are the components of phospholides and how is it formed ?

A

It is a type of lipid formed by the condensation of one molecule of Glycerol, two molecules of fatty acid and a phosphate group

57
Q

What is meant by hydrophilic and hydrophobic ?

A

Hydrophilic = negative phosphate group
Hydrophobic = non polar fatty acids

58
Q

Is glycerol hydrophobic or hydrophilic ?

A

Hydrophilic because of its polar hydroxyl groups

59
Q

Are the hydrocarbon chains of fatty acids and fatty acids hydrophobic or hydrophilic ?

A

Hydrophobic

60
Q

Is the carboxyl group hydrophobic or hydrophilic ?

A

Hydrophilic

61
Q

What are the hydrophilic groups used for

A

To form the ester bond of triglycerides, hence their insolubility in water

62
Q

What is LDL ?

A

Low density lipoprotein :
combination of triglycerides from saturated fats and protein
blocks receptor sites and reduces cholesterol absorption

63
Q

How is LDL raised ?

A

A high intake of fat ( notably saturated fats ) by humans is a contributary factor in heart disease. This raises LDL cholesterol level and increases the incidence of atheromes in coronary arteries.

64
Q

What is atheroma ?

A

Fatty deposit ( plaque ) that builds up in the lining of the artery, causing blockage.

65
Q

Describe the general structure of an amino acid

A

Amine group -NH2
Variable side chain - R
Carboxyl group -COOH
H atom

66
Q

What are proteins ?

A

Polymers of amino acids of which there are twenty types which differ by the R group. They are made up of C, H, O, N and some S.

67
Q

How are two amino acids joined ?

A

Polymerisation occurs by condensation, to form peptide bonds giving rise to dipeptides and polypeptides. The reaction removes a water molecule and forms a peptide bond between the amino acid of one amino acid and the carboxylic acid group of the other.

68
Q

What is the reverse of a condensation reaction ?

A

Hydrolysis which splits a molecule of adding water.

69
Q

What is a polypeptide ?

A

When both the amino end and the carboxylic end of a dipeptide can react with another amino acid so a chain of amino acids can be built up

70
Q

Protein synthesis overview

A

The sequence and number of amino acids is controlled by DNA - this is the primary structure of a protein. In the nucleus, part of a DNA molecules is copied to mRNA. The mRNA leaves through the nuclear pore and goes to the ribosomes where the code is translated into a sequence of amino acids.

71
Q

What are the 4 different structures proteins show ?

A

Primary, secondary, tertiary and quaternary.

72
Q

How and why can proteins carry out different functions ?

A

Each different protein has a specific molecular shape which enables the protein to do its job. The function of each type of protein will be determined by its structure.

73
Q

Primary structure of a protein

A

Primary is the type, number and sequence of amino acids linked /held together by peptide bonds only

74
Q

Secondary structure of a protein

A

Folding of the primary structure. When the polypeptide chain coils to form an alpha helix or fold to form a beta pleated sheet. An alpha helix is formed by weak hydrogen bonding between the peptide bonds in the polypeptide chain.

75
Q

Tertiary structure of a protein

A

It is the folding of the polypeptide chain ( alpha helix ) - eg a globular protein - to form very specific, complex 3D shapes

76
Q

What is the role of the -R groups projecting from the helix in a tertiary structure ?

A

-R groups may interact to form bonds which help to maintain the tertiary structure’s 3D shape.

77
Q

What are the 4 different bonds in the tertiary structure ?

A

Hydrogen bonds between polar R groups (O-H)
Disulphide bonds are covalent bonds formed between sulphurs in the R groups of the amino acid cysteine (S-S)
Ionic bonds between + and - charged R groups of amino acids
Hydrophobic bonds between non polar R groups which tend to cluster together toward the centre if the molecule.

78
Q

Quaternary structure of a protein

A

Where two or more polypeptide chains in tertiary form combine to form complexes joined by bonds similar to those in the tertiary structure. eg Haemoglobin.

79
Q

How are proteins classified ?

A

According to function which is determined by structure.

80
Q

Globular vs Fibrous proteins ?

A

Globular : eg haemoglobin
function as enzymes, antibodies and hormones
rolls up to form balls
soluble in water
wide range of amino acids
metabolic role - carries oxygen in red blood cells
contain prosthetic group (-haem)
Fibrous : eg keratin and collagen
have alpha helices linked into strands
forms fibres, triple helix structure
insoluble in water
35% of amino acids are glycine
structural role - found in skin, tendons, bones
doesn’t contain prosthetic group

81
Q

Haemoglobin features

A

Haem = prosthetic group ( part of protein that is not a protein )
Soluble
Contains iron
Ability to carry lots of oxygen
Oxyhaemoglobin forms from 2 alpha subunits and 2 Beta subunits
Globular

82
Q

Collagen features

A

Fibrous
Triple helix structure - every 3rd amino acid is glycine
insoluble in water
3 chains held together by H bonds
Collagen molecules cross link through covalent bonds to form fibres which give collagen its strength

A level Biology (2 decks)

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