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Biology A-level > 1 Biological Molecules > Flashcards

1 Biological Molecules Flashcards

1
Q

Define monomers

A

Small, basic molecular units. E.g. monosaccharides, amino acids and nucleotides

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2
Q

Define polymers

A

Large, complex molecules composed of long chains on monomers joined together

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3
Q

What is a condensation reaction?

A

A reaction in which 2 molecules join together with the formation of a new chemical bond and involves the elimination of a molecule of water.

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4
Q

What is a hydrolysis reaction?

A

A reaction that breaks a chemical bond between 2 molecules and involves the use of a water molecule.

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5
Q

What are monosaccharides?

A

Monomers from which larger carbohydrates are made. Glucose, galactose and fructose are common monosaccharides.

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6
Q

What does a condensation reaction between two monosaccharides form?

A

A glycosidic bond.

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7
Q

How are disaccharides formed?

A

By the condensation of two monosaccharides.

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8
Q

What is the disaccharide maltose formed from?

A

The condensation of 2 glucose molecules.

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9
Q

What is the disaccharide sucrose formed from?

A

The condensation of a glucose molecule and a fructose molecule.

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10
Q

What is the disaccharide lactose formed from?

A

The condensation of a glucose molecule and a galactose molecule.

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11
Q

What are the 2 isomers of glucose?

A

α-glucose and β-glucose.

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12
Q

How are polysaccharides formed?

A

By the condensation of many glucose units.

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13
Q

How are glycogen and starch formed?

A

By the condensation of α-glucose.

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14
Q

How is cellulose formed?

A

By the condensation of β-glucose.

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15
Q

Describe the structure and function of starch.

A

Starch is a mixture of 2 polysaccharides of α-glucose- amylose and amylopectin:

  • starch is insoluble in water so doesn’t affect water potential, so doesn’t cause water to enter cells by osmosis, which could make them swell so, good for storage
  • cells get energy from glucose, plants store excess glucose as starch so when need more glucose for energy it breaks down starch to release glucose.
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16
Q

Describe the structure and function of glycogen.

A
  • animal cells store excess glucose as glycogen which can be broken down into glucose when energy is needed.
  • structure, long, branched chain of α-glucose and has loads of side branches coming off it. Means that stored glucose can be released quickly, which is important for energy release in animals.
  • very compact molecule so, good for storage as can fit more in a small space.
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17
Q

Describe the structure and function of cellulose.

A
  • long, unbranched chains of β-glucose.
  • when β-glucose molecules bond, form a straight cellulose chains
  • cellulose chains linked together by hydrogen bonds to form microfibrils. The strong fibres mean cellulose provides structural support for cells.
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18
Q

Describe Benedict’s test for reducing sugars.

A
  • add Benedictus reagent to sample
  • heat in water bath
  • if tests positive will form a brick red coloured precipitate.
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19
Q

Describe Benedict’s test for non-reducing sugars.

A
  • add dilute hydrochloric acid to sample and heat
  • neutralise sample with sodium hydrogen-carbonate
  • carry out Benedict’s test for reducing sugar
  • if test positive will produce brick red coloured precipitation, if negative solution will stay blue meaning it doesn’t contain any sugar.
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20
Q

Describe the iodine test for starch

A
  • add iodine dissolved in potassium iodide solution to sample
  • if starch present, sample changes from browny-orange to dark, blue-black colour.
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21
Q

How are triglycerides formed?

A

By the condensation of 1 molecule of glycerol and 3 molecules of fatty acid.

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22
Q

What does a condensation reaction between glycerol and a fatty acid form?

A

An ester bond.

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23
Q

What is meant by a saturated fatty acid?

A

Saturated fatty acids don’t have any double bonds between their carbon atoms. The fatty acid is ‘saturated’ with hydrogen.

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24
Q

What is meant by an unsaturated fatty acid?

A

Unsaturated fatty acids have at least one double bond between carbon atoms, which can cause the chain to kink.

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25
Q

How does a phospholipid differ from a triglyceride?

A

One of the fatty acids of a triglyceride is substituted by a phosphate group

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26
Q

Describe structure of triglycerides related to their properties.

A
  • large, non polar so insoluble in water. As a result their storage doesn’t affect osmosis in cells or the water potential of them
  • have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms and are therefore good source of energy.
  • low mass to energy ratio, makes them good storage molecules because much energy stored in small volume. Beneficial to animals as reduces mass they have to carry as they move around.
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27
Q

Describe properties of phospholipids related to their structure.

A
  • have hydrophilic heads and hydrophobic tails so form a double layer with their heads facing out towards the water on either side.
  • centre of bilateral is hydrophobic, so water-soluble substances can’t easily pass through it, the membrane acts as a barrier to those substances.
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28
Q

Explain the emulsion test For testing lipids (fats).

A
  • shake test substance wit ethanol for about 1 minute so that it dissolves, the pour solution into water.
  • any lipid will show up as a milky emulsion.
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29
Q

In the structure of an amino acid what does the NH2 represent?

A

An amine group.

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30
Q

In the structure of an amino acid what the does the COOH represent?

A

A carboxyl group.

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31
Q

In the structure of an amino acid what does R represent?

A

A side chain, the 20 amino acids that are common in all organisms differ only in their side group.

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32
Q

What does the condensation reaction between 2 amino acids form?

A

A peptide bond.

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33
Q

How are dipeptides formed?

A

By condensation reaction of 2 amino acids.

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34
Q

How are polypeptides formed?

A

By the condensation of many amino acids.

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35
Q

What might a functional protein contain?

A

One ore more polypeptides.

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36
Q

what is the primary structure of proteins?

A

The sequence of amino acids in the polypeptide chain.

37
Q

What is the secondary structure of a protein?

A

Polypeptide chain doesn’t remain flat and straight, hydrogen bonds form between amino acids. Making it coil into an alpha helix or fold into a beta pleated sheet.

38
Q

What is the tertiary structure of a protein?

A

Coiled/ folded chain is often coiled and folded further. More bonds form between different parts of polypeptide chain, including hydrogen bonds and ionic bonds. Disulphides bridges also form whenever 2 molecules of amino acid cysteine come close together. For proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure.

39
Q

What is the quaternary structure of a protein?

A

The way these polypeptide chains are assembled together. For proteins made from more than 1 polypeptide chain, the quaternary structure is the protein’s final 3D structure.

40
Q

Describe the structure and shape of enzymes.

A
  • usually roughly spherical in shape due to tight folding of polypeptide chains.
  • soluble and often have roles in metabolism.
41
Q

Describe the structure and shape of antibodies.

A
  • made up of 2 light polypeptide chains and 2 heavy polypeptide chains bonded together.
  • have variable regions in which the amino acid sequence in these regions vary greatly.
42
Q

Describe the structure and shape of transport proteins.

A
  • eg channel proteins present in cell membrane.
  • channel proteins contain hydrophobic and hydrophilic amino acids causing the protein to fold up and form a channel. These proteins transport molecules and ions across membranes.
43
Q

Describe the structure and shape of structural proteins.

A
  • physically strong.

- consists of long polypeptide chains lying parallel to each other with cross-links between them.

44
Q

Describe the biuret test for proteins.

A
  • add few drops of sodium hydroxide solution. To make test solution alkaline.
  • then add copper sulfate solution.
  • if protein present solution turns purple of not solution stays blue.
45
Q

How do enzymes effect the activation energy?

A

Enzymes lower the amount of activation energy that’s needed, making reactions happen at a lower temperature than they could without an enzyme. This speeds up reaction.

46
Q

What is the induced-fit model of enzyme action?

A
  • Explains why enzymes are so specific and only bond to 1 particular substrate.
  • substrate doesn’t only have to be right shape to fit active site, it has to make active site change shape in right way as well.
  • as substrate binds the active site changes shape slightly.
47
Q

How do enzymes properties relate to their tertiary structure?

A
  • very specific, usually only catalyse 1 reaction. Because only 1 complementary substrate will fit into active site.
  • active site shape determined by enzymes tertiary structure.
  • each different enzyme has different tertiary structure and so different shaped active site, if substrate shape doesn’t match active site, no enzyme-substrate complex formed and reaction won’t be catalysed.
  • if tertiary structure altered, active site shape changed so substrate wont fit and no enzyme-substrate complex formed and enzyme will no longer be able to carry out its function.
48
Q

Why is the lock and key model of enzyme action no longer widely accepted?

A
  • substrate fits into enzyme in same key fits into a lock
  • enzyme and substrate do fit together in first place, but new evidence showed that enzyme-substrate complex changed shape slightly to complete the fit. This locks substrate even more tightly to enzyme.
49
Q

How does temperature affect rate of enzyme controlled reactions?

A
  • rise temperature makes enzyme’s molecule molecule
  • if temperature goes above certain level, vibration breaks some of bonds that hold enzyme in shape
  • active site changes shape and enzyme and substrate no longer fit together
  • the enzyme is denatured.
50
Q

How does pH affect rate of enzyme controlled reactions?

A
  • all enzymes have an optimum pH
  • most human enzymes work best at pH7 but pepsin works best at pH2 useful because found in stomach
  • above and below optimum pH the H+ and OH- ions can mess up the ionic bonds and hydrogen bonds that hold the enzyme’s tertiary structure in place. This makes active site change shape so enzyme denatured.
51
Q

How does enzyme concentration affect rate of enzyme controlled reactions?

A
  • more enzyme molecules in solution, more likely collisions with substrate molecules to form enzyme-substrate complex
  • so increase rate of reaction.
  • if amount of substrate limited, there comes point when there’s ore than enough enzyme molecules to deal with all the available substrate, so adding more enzyme has no further effect.
52
Q

How does substrate concentration affect rate of enzyme controlled reactions?

A
  • higher substrate concentration, faster reaction. More substrate molecules means more collisions and so more active sites will be used.
  • only true up until saturation point, as after there are so many substrate molecules that that all the active sites are full and adding more makes no difference.
  • substrate concentration decreases with time, so rate of reaction decreases over time too.
53
Q

What does a competitive inhibitor do?

A
  • competitive inhibitor molecules have similar shape to substrate molecule.
  • they compete with substrate molecules to bind to the active site, but no reaction takes place.
  • instead they block the active site, so no substrate molecules can fit in.
54
Q

Describe how competitive inhibition can effect enzyme activity.

A
  • how much the enzyme is inhibited depends on relative concentrations of inhibitor and substrate.
  • high concentration of inhibitor, it’ll take up nearly all active sites and hardly any substrate will get to enzyme.
  • higher concentration of substrate, substrates chance of getting to active site before inhibitor increases, so increasing rate of reaction.
55
Q

What does a non-competitive inhibitor do?

A
  • bind to enzyme away from its active site.

- causing active site to change shape so substrate molecule can no longer bind to it.

56
Q

Describe how non-competitive inhibition can effect enzyme activity.

A

-increasing concentration of substrate won’t make any difference to reaction rate- enzyme activity will still be inhibited.

57
Q

Why are DNA and RNA important information carrying molecules?

A
  • In all living cells, DNA holds genetic information needed for growth and development.
  • RNA transfers genetic information from DNA to the ribosomes. Ribosomes are made from RNA and proteins.
58
Q

What are the components of a DNA nucleotide?

A
  • deoxyribose
  • a phosphate group
  • organic base (adenine, cytosine, guanine, thymine)
59
Q

DNA and RNA are polymers of nucleotides. What forms a nucleotide?

A

A pentose sugar, a nitrogen containing organic base and a phosphate group.

60
Q

What are the components of an RNA nucleotide?

A
  • ribose
  • a phosphate group
  • organic bases ( adenine, cytosine, guanine, uracil)
61
Q

What does a condensation reaction between 2 nucleotides form?

A

Phosphodiester bond.

62
Q

Describe the structure of DNA.

A

2 antiparallel polynucleotide strands twist to form double helix, held together by hydrogen bonds between specific complementary base pairs (2 hydrogen bonds between A and T, 3 hydrogen bonds between C and G).

63
Q

Describe the structure of RNA.

A

Made from a single polynucleotide chain and is much shorter that most DNA polynucleotides.

64
Q

What is the first step of semi-conservative replication of DNA.

A
  • enzyme DNA helicase breaks hydrogen bonds between bases on the 2 polynucleotide DNA strands
  • this makes helix unwind
  • forms 2 single strands.
65
Q

What is the second step of semi-conservative replication of DNA.

A
  • each original single strand acts as template for a new strand.
  • complementary base pairing means free-floating DNA nucleotides are attracted to their complementary exposed bases.
66
Q

What is the third step of semi-conservative replication of DNA.

A
  • condensation reactions join the Adjacent nucleotides of new strands together, catalysed by enzyme DNA polymerase
  • hydrogen bonds form between bases on original and new strand.
67
Q

What is the outcome of semi-conservative replication of DNA.

A

Each new DNA molecule contained one strand from original DNA molecule and one new strand.

68
Q

Explain why DNA moves in opposite ways along anti parallel DNA strands.

A
  • active site of DNA polymerase only complementary to 3’ end of the newly forming DNA strand, so enzyme can only add nucleotides to new strand at 3’ end.
  • means new strand is made in 5’ to 3’ direction and that DNA polymerase moves down template strand in a 3’ to 5’ direction
  • because strands in double helix are antiparallel DNA polymerase on 1 strand moves in opposite direction to one on other strand.
69
Q

What were the two hypothesis of Meselson and Stahl test to provide evidence for semi-conservative replication.

A
  • conservative model, suggested that original DNA molecule remained intact and a separate DNA copy was built up.
  • semi-conservative model, suggested that original DNA molecule split into 2 separate strands, and complimentary free nucleotides would join to those strands.
70
Q

What 3 facts did Meselson and Stahl base their work on ?

A
  • all bases in DNA contain nitrogen
  • nitrogen has 2 forms: lighter nitrogen 14N and the heavier isotope 15N
  • bacteria will incorporate nitrogen from their growing medium into any new DNA they make
71
Q

Describe how Meselson and Stahl experiment worked.

A
  • 2 samples bacteria grown,one in nutrient broth containing light nitrogen and one in broth containing heavy nitrogen. Bacteria reproduce and took up nitrogen to help make nucleotides for DNA.
  • sample taken from each batch of bacteria and spun in centrifuge, DNA from heavy nitrogen bacteria settled lower than DNA from light nitrogen bacteria.
  • bacteria from heavy nitrogen broth taken and put in broth containing only light nitrogen and left for one round of DNA replication and then another sample was taken, and spun in centrifuge.
  • results: DNA settled out in middle showing DNA molecule contained mixture of heavy and light nitrogen, so bacterial DNA had replicated semi-conservatively.
72
Q

What is a single molecule of ATP

A

A nucleotide derivative formed from a molecule of ribose, a molecule of adenine and 3 phosphate groups.

73
Q

Describe how ATP is made and quickly used.

A
  • hydrolysis of ATP makes ADP and Pi, a phosphate bond is broken and energy is released
  • hydrolysis reaction catalysed by enzyme ATP hydrolyse
  • ATP hydrolysis can be coupled to other energy requiring reactions in the cell, this means the energy released can be used directly to make coupled reaction happen, rather than being lost to heat.
74
Q

How can the inorganic phosphate released during the hydrolysis of ATP be used?

A

To phosphorylate other compounds, often making them more reactive.

75
Q

How can ATP be re-synthesised?

A

By the condensation of ADP and Pi, this reaction is catalysed by enzyme ATP synthase during photosynthesis or respiration.

76
Q

Describe water as a metabolite.

A

acts as metabolite in many metabolic reactions, including condensation and hydrolysis reactions.

77
Q

Describe why water has a high latent heat of vaporisation.

A
  • takes a lot of energy to break hydrogen bonds between water molecules
  • water has high latent heat of vaporisation, lot of energy used up when water evaporates
  • useful for living organisms because means they can use water loss through evaporation to cool down without losing too much water
78
Q

Describe how water can buffer changes in temperature.

A
  • hydrogen bonds between water molecules can absorb lot of energy
  • so water has a high specific heat capacity, takes a lot of energy to heat up
  • useful for living organisms because means that water doesn’t experience rapid temperature changes. This makes water good habitat because temperature under water likely to be more stable. Water inside organisms also remains fairly stable temperature, helping them maintain constant internal body temperature.
79
Q

Describe why water is a good solvent.

A
  • lot of important substances in metabolic reactions are ionic, means they’re made from 1 positively charged atom or molecule and 1 negatively charged atom or molecule
  • water is polar, positive end attracted to negative ion, and negative end attracted to positive ion.
  • means ions will get totally surrounded by water molecules, they’ll dissolve.
  • so waters polarity makes it a useful solvent.
80
Q

Describe the strong cohesion between water molecules.

A
  • cohesion is attraction between molecules of same type, water molecules are very cohesive because they’re polar.
  • strong cohesion helps water to flow, making it great for transporting substances
  • strong cohesion also means water has high surface tension when comes into contact with air. This is reason why sweat forms droplets, wh I evaporates from skin to cool organism down. Also reason pond skaters and some insects can walk on surface of pond.
81
Q

Where do inorganic ions occur?

A

In solution in the cytoplasm and body fluids of organisms. Each ion has specific role, depending on its properties. An ions role determines whether its found in high or low concentration.

82
Q

Why are iron ions important part of Haemoglobin?

A
  • haemoglobin is a large protein that carries oxygen around the body, in red blood cells
  • made up of 4 different polypeptide chains, each with an iron ion in the centre
  • its the Fe2+ that actually binds to oxygen in haemoglobin
  • when oxygen is bound, the Fe2+ ion temporarily becomes an Fe3+ ion, until oxygen is released.
83
Q

Why do hydrogen ions determine the pH?

A

pH calculated based on concentration of hydrogen ions in the environment. The more H+ present, the lower the pH. Enzyme-controlled reactions are all affected by pH.

84
Q

Describe how sodium ions help transport glucose and amino acids across membranes.

A
  • glucose and amino acids needs a bit of help crossing cell membranes.
  • molecule of glucose or an amino acid can be transported into a cell alongside sodium ions. This is known as co-transport.
85
Q

Describe phosphate ions as an essential component of ATP and DNA.

A
  • when phosphate ion is attached to another molecule, its know as a phosphate group.
  • DNA, RNA and ATP all contain phosphate groups.
  • it’s bonds between phosphate groups that store energy in ATP.
  • the phosphate groups in DNA and RNA allow nucleotides to join up to form polynucleotides.
86
Q

What are ribosomes formed from?

A

RNA and proteins.

87
Q

Describe structure related to function of amylose

A

~amylose- long, unbranched chain of α-glucose. The angles of glycosidic bonds give it a coiled structure. This makes it compact, so good for storage as can fit more in a small space.

88
Q

Describe the structure related to function of amylopectin.

A

~amylopectin- long, branched chain of α-glucose. Side branches allow enzymes that break down the molecule to get at the glycosidic bonds easily, meaning glucose can be released quickly

Biology A-level (15 decks)

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