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A-level Biology > 2.3 - Biological molecules > Flashcards

2.3 - Biological molecules Flashcards

1
Q

What are monomers?

A

smaller units from which larger molecules are made

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2
Q

What are polymers?

A

molecules made from a large number of monomers joined together

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3
Q

What is a condensation reaction?

A

A reaction that joins two molecules together to form a chemical bond whilst eliminating a molecule of water

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4
Q

What is a hydrolysis reaction?

A

a reaction that breaks a chemical bond between two molecules and involves the use of a water molecule

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5
Q

What is a monosaccharide?

A

monomers from which larger carbohydrates are made

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6
Q

How is a glycosidic bond formed?

A

a condensation reaction between two monosaccharides

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7
Q

Name three main examples of polysaccharides

A

glycogen, starch, cellulose

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8
Q

Describe Benedict’s test for reducing sugars

A

gently heat a solution of a food sample with an equal volume of Benedict’s solution for five minutes, the solution turns orange/brown if reducing sugar is present

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9
Q

Name the two main groups of lipids

A

phospholipids, triglycerides (fats and oils)

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10
Q

Give four roles of lipids

A

source of energy, water proofing, insulation, protection

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11
Q

What is an ester bond?

A

a bond formed by a condensation reaction between glycerol and a fatty acid

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12
Q

Describe the emulsion test for lipids

A

mix the sample with ethanol in a clean test tube, shake sample, add water, shake again. A cloudy white colour indicates lipid is present

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13
Q

What are the monomers that make up proteins?

A

amino acids

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14
Q

How is a peptide bond formed?

A

a condensation reaction between two amino acids. The amine and carboxyl groups of two amino acids join through the release of water

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15
Q

What is a polypeptide?

A

many amino acids joined together

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16
Q

Describe the biuret test for proteins

A
  • mix the sample with sodium hydroxide solution at room temperature
  • add very diluted copper(II) sulfate solution
  • mix gently
  • a purple colour indicates that peptide bonds are present
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17
Q

How does an enzyme affect a reaction?

A

it lowers the activation energy

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18
Q

Give five factors that can affect enzyme action

A

temperature, pH, enzyme concentration, substrate concentration, inhibitor concentration

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19
Q

What is a competitive inhibitor?

A

a molecule with a similar shape to the substrate, allowing it to occupy the active site of the enzyme

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20
Q

What is a non-competitive inhibitor?

A

a molecule that changes the shape of the enzyme by binding somewhere other than the active site

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21
Q

What are the similarities and differences between alpha glucose and beta glucose?

A

Both 6C hexose monosaccharides with a ring structure
Alpha glucose - the hydroxyl (OH) group on carbon 1 is below the plane
Beta glucose - the hydroxyl (OH) group on carbon 1 is above the plane

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22
Q

How do hydrogen bonds form between water molecules?

A

Water is polar, as oxygen has a much greater share of electrons in an O-H bond than water, making O slightly negative and H slightly positive. This means there is a weak intermolecular attraction between the O- and H+ on adjacent molecules, forming weak hydrogen bonds.

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23
Q

What are some biologically important properties of water?

A
  • an unusually high boiling point due to hydrogen bonding
  • Cohesive properties (moves as one mass through a straw etc as molecules are attracted to each other)
  • have a ‘skin’ of surface tension due to cohesion
  • adhesive properties
  • good solvent for chemical reactions
  • is stable so forms a constant environment for habitats
  • ice is less dense than water, acts as an insulator
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24
Q

Name the elements found in carbohydrates, lipids, proteins and nucleic acids

A

carbohydrates - C, H, O
lipids - C, H, O
proteins - C, H, O, N, S
nucleic acids - C, H, O, N, P

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25
Q

What monosaccharides are the three main disaccharides made out of?

A

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

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26
Q

What are the properties and structure of starch?

A

Starch is how glucose made from photosynthesis is stored in plant cells
It is a chemical energy store made up of 2 polysaccharides
Amylose = helix shape made up of alpha-glucose joined by 1-4 glycosidic bonds (compact and insoluble due to helix from H-bonding and bond positioning)
Amylopectin = 1-4 glycosidic bonds between alpha-glucose but also some 1-6 bonds to form a branched structure.

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27
Q

What are the structure and properties of glycogen?

A

Energy storage molecule in animals and fungi. Forms more branches than amylopectin, meaning it is more compact. Ideal for storage and more free ends where molecules can be added and removed, as animals are mobile so need more energy.
Insoluble, 1-4 and 1-6 glycosidic bonds between alpha-glucose molecules

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28
Q

What are the structure and properties of cellulose?

A

1-4 glycosidic bonds between beta-glucose, every other beta-glucose is turned upside down to form a straight chain molecule.
Cellulose molecules make hydrogen bonds with each other forming microfibrils, which form macrofibrils. These are strong and insoluble and used to make plant cell walls.

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29
Q

Why does cellulose form an important part of out diet?

A

It is very hard to break down into its monomers so forms the ‘fibre’ or ‘roughage’ required for a healthy digestive system

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30
Q

Describe a test for starch

A

Iodine test:
- a few drops of iodine dissolved into potassium iodide solution are mixed with a sample
- If the solution changes from yellow/brown to purple/black then starch is present in the sample

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31
Q

Why are lipids insoluble in water?

A

They are non-polar as the electrons that form bonds are more evenly distributed

32
Q

How is a triglyceride made?

A

By combining one glycerol molecule with three fatty acids

33
Q

What is the difference between saturated and unsaturated fatty acids

A

Saturated fatty acids have no double bonds present between carbons because they are saturated with the maximum number of hydrogen atoms. These are normally more unhealthy solid fats.
Unsaturated fatty acids have double bonds between some of its carbon atoms, causing the molecule to kink or bend, making them liquid at room temperature. Normally more healthy plant oils

34
Q

What are phospholipids?

A
  • modified triglycerides
  • one of the fatty acid chains is replaced by a phosphate group
  • they have a non-polar/hydrophobic fatty acid tail and a charged/hydrophilic phosphate head
  • called surfactants as they will form a layer on the surface of water
  • also form a bilayer in water, so crucial in the formation of plasma membranes
35
Q

Sterols

A
  • steroid alcohols
  • a type of lipid
  • also found in cells
  • complex alcohol molecules, based on a 4C ring with a hydroxyl group
  • also has dual hydrophilic and hydrophobic characteristics
36
Q

Cholesterol

A
  • a sterol
  • body manufactures cholesterol in the liver and intestines
  • has an important role in plasma membranes
  • adds stability and regulates fluidity by keeping membranes fluid at low temperatures and stopping them becoming too fluid at high temperatures
37
Q

What structural difference results in different amino acids?

A

Different R-groups result in different amino acids

38
Q

What are the levels of protein structure

A

Primary
Secondary
Tertiary
Quarternary

39
Q

What is the primary level of protein structure?

A

The sequence of amino acids. Directed by the DNA sequence. Influences the folding of the polypeptide. Peptide bonds join the amino acids together

40
Q

What is the secondary level of protein structure

A

The nitrogen, hydrogen and oxygen atoms of the repeating structure of amino acids interact. Hydrogen bonds within the chain can coil it, resulting in an alpha-helix structure. Hydrogen bonds between chains results in a flat beta-pleated sheet structure

41
Q

What is the tertiary level of protein structure

A

The folding of a protein into its final, complex shape. The secondary structure brings the R-groups of different amino acids closer, interacting by forming:
- hydrophilic and hydrophobic interactions
- hydrogen bonds (weak)
- ionic bonds
- disulfide bridges (sulfur, covalent, strong)

42
Q

What is the quaternary level of protein structure

A
  • some proteins do not have a quaternary structure
  • the association between two or more subunits (individual proteins)
  • interactions are the same as the tertiary structure but between subunits
  • subunits can be identical or different
  • enzymes often consist of two identical subunits
  • haemoglobin has 4 subunits, 2 sets of identical alpha chains and 2 sets of identical beta chains, with haem groups
43
Q

Breakdown of proteins (in digestion)

A

Proteases catalyse proteins turning back into their amino acids.
In a hydrolysis reaction, water is used to break peptide bonds, reforming the amine and carboxylic acid groups

44
Q

Globular proteins

A
  • compact
  • water soluble (hydrophilic R-groups are on the outside) usually spherical in shape
  • formed when tertiary structure forms in a way that means the hydrophobic R-groups are kept away from the aqueous environment
45
Q

Insulin

A

Globular protein
- hormone involved in regulation of blood glucose concentration
- hormones are transported in bloodstream, so need to be soluble
- need to have a specific shape to fit to receptors

46
Q

Conjugated proteins

A

globular proteins that contain a non-protein component called a prosthetic group. Prosthetic groups include lipoproteins, glycoproteins and haem (contain an iron ion)

47
Q

Haemoglobin

A

Conjugated protein
- each subunit contains a prosthetic haem group
- iron ion in each haem group can reversible combine with an oxygen molecule

48
Q

Catalase

A

Globular protein
-enzyme
- contains 4 haem prosthetic groups
- Iron II groups allow catalase to speed up breakdown of b
hydrogen peroxide (toxic biproduct of metabolism)

49
Q

Fibrous proteins

A

Formed from long insoluble molecules due to a large proportion of hydrophobic R-groups
- contain limited range of amino acids, so they are usually repetitive, resulting in an organised structure
- do not form into complex 3D shapes like globular proteins

50
Q

Keratin

A

Group of fibrous proteins present in hair, skin and nails
- high proportion of cysteine results in strong disulfide bonds
- degree of sulfide bonds determine flexibility

51
Q

Elastin

A
  • fibrous protein
  • found in elastic fibres (in walls of blood vessels and alveoli)
  • allows structures to stretch and recoil
52
Q

Collagen

A

Fibrous protein
- connective tissue found in skin, tendons, ligaments and nervous system
- compact and flexible
- provides high tensile strength
- 2 polypeptides tightly wound together

53
Q

What are nucleic acids

A

Large polymers formed from many nucleotides linked together in a chain that were found in the cell nucleus
two types:
- DNA
- RNA
Have roles in the storage and and transfer of genetic information and the synthesis of polypeptides. The basis for heredity

54
Q

What is a nucleotide made up of

A
  • a pentose monosaccharide (ribose or deoxyribose)
  • a phosphate group
  • a nitrogenous base
55
Q

How are nucleotides linked together

A

Phosphodiester bonds. Condensation reactions. Forms a polymer called a polynucleotide. Phosphate group at carbon 5 forms a covalent bond with the hydroxyl group on carbon 3. Forms a long, strong sugar-phosphate backbone

56
Q

How is DNA different to RNA

A

DNA (deoxyribonucleic acid) contains a deoxyribose sugar with one fewer oxygen atoms that ribose, in RNA (ribonucleic acid)

57
Q

What 2 groups are the nitrogenous bases divided into

A

Pyrimidines:
- smaller bases that contain single carbon ring structures
- Thymine (T) and Cytosine (C)
Purines:
- larger bases containing double carbon ring structures
- Adenine (A) and Guanine (G)

58
Q

What are the DNA base pairings

A
  • Thymine and Adenine form 2 hydrogen bonds
  • Cytosine and Guanine form 3 hydrogen bonds
59
Q

Why is the double helix said to be antiparallel?

A

The two parallel strands making up the double helix run in opposite directions.

60
Q

What is the structure of the double helix?

A

It is made up of two antiparallel polynucleotide strands held together by hydrogen bonds between corresponding bases. The double strand is coiled into a helix

61
Q

What is the difference between RNA and DNA

A

RNA:
- ribose sugar
- Uracil base instead of Thymine
- single strand
- binds to DNA
- mRNA, tRNA and rRNA
DNA:
- deoxyribose sugar
- Thymine base
- double helix
- hydrogen bonds
- antiparallel
- complimentary base pairs
- does not leave nucleus in eukaryotes

62
Q

Semi-conservative DNA replication

A

The two new molecules of DNA produced each consist of one old strand and one new strand of DNA.
- DNA helicase causes the two strands of DNA to separate
- free nucleotides that have been activated are attracted to their complimentary base pairs
- once the nucleotides are joined up, they are joined by DNA polymerase
- 2 identical molecules of DNA are formed

63
Q

What is a codon

A

A sequence of three bases in the genetic code. Each codon codes for an amino acid

64
Q

What is a gene

A

A section of DNA that contains the complete sequence of bases/codons to code for an entire protein.
The genetic code is universal

65
Q

Degenerate code

A

There are more codons than amino acids (64 to 20), so many amino acids can be coded for by more than one codon

66
Q

Why is transcription needed

A

Chromosomal DNA is too large to leave the nucleus, so the base sequence of genes have to be copied ad transported to the site of protein synthesis, using RNA

67
Q

The process of transcription

A
  • RNA polymerase binds to the target gene
  • DNA helicase unwinds the double strands (H bonds break)
  • DNA strands separate and bases of target gene are exposed
  • RNA polymerase binds complimentary free-floating RNA nucleotides to template strand
  • RNA forms mRNA
  • RNA reaches a stop codon and mRNA separated by RNA polymerase
  • DNA H-bonds reform
  • mRNA leaves the nucleus
68
Q

The process of translation

A
  • mRNA binds to a ribosome in the cytoplasm
  • 2 codons can fit inside the ribosome at one time
  • one molecule of tRNA binds to the first codon in the ribosome. The tRNA molecule has an anticodon complimentary to a specific codon.
  • each tRNA carried a specific amino acid, bound with ATP
  • the 2 amino acids in the ribosome form a peptide bond
  • creates a polypeptide chain as the mRNA moves along the ribosome
  • when the ribosome reaches a stop codon, there is no corresponding amino acid, so the polypeptide chain is released
69
Q

What are the different types and functions of RNA

A

mRNA:
- messenger RNA
- transports genetic code from nucleus to ribosome
- breaks down after protein synthesis
tRNA:
- transfer RNA
- a strand of RNA folded so the anticodon (loop) is at one end of the molecule and the point of attachment of an amino acid is at the other end
rRNA:
- ribosomal RNA
- what ribosomes are made of

70
Q

Which strand of DNA contains the code for proteins to be synthesised?

A

The sense strand that runs from 5’ to 3’. The antisense strand runs from 3’ to 5’, which is the one that acts as a template strand so the RNA will have the same bases as the sense strand

71
Q

What three main functions do cells require energy for?

A
  • synthesis
  • transport
  • movement
72
Q

what is the structure of ATP

A

Adenosine triphosphate
- a ribose (pentose sugar) that has an adenine base on carbon 1 and 3 phosphate groups on carbon 5.
- the removal of a phosphate group to form ADP (adenosine diphosphate) through hydrolysis releases energy
- the phosphate group can reattach through a condensation reaction (phosphorylation)

73
Q

What are the adaptations of ATP

A

ATP is used as a universal energy currency. It is:
- small
- water soluble
- is an intermediate energy source that releases energy in small quantities (no energy lost as heat)
- easily regenerated/recharged with energy

74
Q

The difference between thin layer and paper chromatography

A

Paper chromatography:
- paper stationary phase
- solute sometimes merges on chromatogram
Thin layer chromatography:
- inert stationary phase e.g. silica
- solute separation is clearer

75
Q

What are some examples of cations

A

Calcium (Ca2+)
- transmission across synapses and muscle contractions
Sodium (Na+)
- involved in conservation of water in the kidneys
- transmission of action potential across neurone
Potassium (K+)
- transmission of nerve impulses across neurone
- turgidity of guard cells
Hydrogen (H+)
- involved in photosynthesis and respiration
Ammonia (NH+)
- source of nitrogen for amino acid production in plants

76
Q

Examples of anions

A

Nitrate
- plants use to make amino acids and nucleotides
Hydrogen carbonate (HCO3-)
- transport of CO2 in humans
- found in bile to neutralise stomach acid
Phosphate
- nucelotides and ATP
Hydroxide (OH-)
- maintains pH levels

A-level Biology (24 decks)

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