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2023-25 Biology > 1: Biological Molecules > Flashcards

1: Biological Molecules Flashcards

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1
Q

What is a monomer?

A

A monomer is a small identical / similar repeating unit / molecule from which larger molecules / polymers are made;

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2
Q

What is a Polymer?

A

Molecule made up of THREE or MORE / many identical/similar molecules/monomers.

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3
Q

What term is used to describe the different structures of α-glucose and β-glucose?

A

Isomer(ism)

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4
Q

A starch molecule has a spiral shape. Explain why this shape is important to its function in cells.

A
  • Compact
  • occupies small space
  • tightly packed;
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5
Q

The structure of cellulose is related to its role in plant cell walls. Explain how. (3)

A
  • Long, straight, unbranched chains of Beta glucose;
  • (Joined by) many WEAK hydrogen bonds;
  • Form microfibrils / macrofibrils;
  • Provide rigidity/strength/support;

Reject reference to strong

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6
Q

Compare and contrast the structure of starch and the structure of cellulose. [6 marks]

A
  1. Both polysaccharides OR Both are glucose polymers OR Both are made of glucose monomers;
  2. Both contain glycosidic bonds (between monomers);
  3. Both contain carbon, hydrogen and oxygen/C, H and O;
  4. Starch has α-glucose and cellulose has β-glucose;
  5. Both polysaccharides OR Both are glucose polymers OR Both are made of glucose monomers;
  6. Both contain glycosidic bonds (between monomers);
  7. Both contain carbon, hydrogen and oxygen/C, H and O;
  8. Starch has α-glucose and cellulose has βglucose;
  9. Starch (molecule) is helical/coiled and cellulose (molecule) is straight;
  10. Starch (molecule) is branched and cellulose is not/unbranched;
    7.Cellulose has (micro/macro) fibrils and starch does not;
  11. Starch has 1–6 glycosidic bonds and cellulose does not
    OR Starch contains two types of molecule and cellulose contains one type of molecule
    OR Starch is amylose and amylopectin and cellulose is one type of molecule;
    cellulose has β-glucose;
  12. Starch (molecule) is helical/coiled and cellulose (molecule) is straight;
  13. Starch (molecule) is branched and cellulose is not/unbranched;
    7.Cellulose has (micro/macro) fibrils and starch does not;
  14. Starch has 1–6 glycosidic bonds and cellulose does not
    OR Starch contains two types of molecule and cellulose contains one type of molecule
    OR Starch is amylose and amylopectin and cellulose is one type of molecule;
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7
Q

Give one feature of starch and explain how this feature enables it to act as a storage
substance.

A
  • Helical / spiral So compact / tightly packed / can fit (lots) into a small space;
  • Insoluble So no osmotic effect / does not leave cell / does not affect water potential;
  • Large molecule / long chain So does not leave cell / contains large number of glucose units;
  • Branched chains So rapid hydrolysis to remove glucose for respiration;
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8
Q

Hydrogen bonds are important in cellulose molecules. Explain why.

A
  • Holds chains/cellulose molecules together/forms cross links between chains/cellulose molecules/forms microfibrils;
  • Providing strength/rigidity (to cellulose/cell wall);
  • Weak Hydrogen bonds provide strength in large numbers;
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9
Q

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.

A
  • Glucose and galactose
  • Joined by condensation
  • Joined by glycosidic bond
  • Added to polypeptide in Golgi
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10
Q

Describe how the student would show that reducing sugars were present in a solution. [3]

A
  1. Add Benedict’s;
  2. Heat to 95°C;
  3. Red/orange/yellow/green precipitate (shows reducing sugar present);
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11
Q

Describe how you would test a sample of food for the presence of starch. [2]

A
  1. Add potassium iodide (KI) solution to the food sample;
  2. Blue/black/purple indicates starch is present;
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12
Q

Describe how you would test a liquid sample for the presence of a lipid and how you would recognise a positive result. [2]

A
  1. (Mix / shake sample) with ethanol, then water and shake;
  2. Cloudy White / milky (emulsion);
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13
Q

Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid?

A
  • Double bond(s);
  • (Bonds) between carbon atoms within the hydrocarbon chain;
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14
Q

Describe how an ester bond is formed in a phospholipid molecule. [2]

A
  1. Condensation (reaction) OR Loss of water;
  2. Between of glycerol and fatty acid;
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15
Q

Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids. (3)

A
  1. Crush/grind;
  2. With ethanol/ alcohol, to dissolve the lipid;
  3. Then add water then shake;
  4. Forms a white emulsion / goes white;
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16
Q

What are the differences between a triglyceride and a phospholipid? [2]

A
  1. Fatty acid removed;
  2. Replaced with a phosphate group;
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17
Q

Compare and contrast the structure and properties of triglycerides and phospholipids [5]

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 are also contain P
  • Triglyceride has three fatty acids and phospholipids have two fatty acids plus phosphate group
  • Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region
  • Phospholipids form monolayer/micelle/bilayer but triglycerides don’t.
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18
Q

Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample. [6]

A

Lipid
1. Add ethanol/alcohol then add water and shake/mix OR Add ethanol/alcohol and shake/mix then pour into/add water;
2. White/milky emulsion OR emulsion test turns white/milky;

Non-reducing sugar
3. Do Benedict’s test and stays blue/negative;
4. Boil with acid then neutralise with alkali;
5. Heat with Benedict’s and becomes red/orange (precipitate);

Amylase
6. Add biuret (reagent) and becomes purple/violet/mauve/lilac;
7. Add starch, (leave for a time), test for reducing sugar/absence of starch;

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19
Q

A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution. [2]

A
  1. Filter and dry (the precipitate);
  2. Find mass/weight;
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20
Q

Describe the structure of proteins. [5]

A
  • Polymer of amino acids;
  • Joined by peptide bonds;
  • Formed by condensation reactions;
  • Primary structure is number AND order/sequence of amino acids;
  • Secondary structure is folding of polypeptide chain into Alpha-helix and Beta-pleated sheets **due to hydrogen bonding; **
  • Tertiary structure is 3-D folding due to hydrogen bonding and ionic bonding and disulfide bridges;
  • Quaternary structure is two or more polypeptide chains joined together;
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21
Q

Describe how the structure of a protein depends on the amino acids it contains. [5]

A
  1. Structure is determined by (relative) position of amino acid/R group/interactions;
    Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / hydrophobichydrophilic interactions
  2. Primary structure is sequence/order of amino acids;
  3. Secondary structure formed by hydrogen bonding (between amino acids);
    Accept alpha helix/β-pleated sheet for ‘secondary structure’
  4. Tertiary structure formed by interactions (between R groups);
    Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / hydrophobichydrophilic interactions
  5. Creates active site in enzymes OR Creates complementary/specific shapes in antibodies/carrier proteins/receptor (molecules);
  6. Quaternary structure contains >1 polypeptide chain OR Quaternary structure formed by interactions/bonds between polypeptides; Accept prosthetic (group)
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22
Q

Describe how a peptide bond is formed between two amino acids to form a dipeptide [2]

A
  1. Condensation (reaction) / loss of water;
  2. Between amine / NH2 and carboxyl / COOH;
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23
Q

Describe how monomers join to form the primary structure of a protein. [3]

A
  1. Condensation reaction between amino acids;
  2. (Forming) peptide bonds;
  3. Creating (specific) sequence/order of amino acids;
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24
Q

Describe how an enzyme-substrate complex increases the rate of reaction [2]

A
  1. Reduces activation energy
  2. Due to bending bonds OR Without the enzyme, very few substrates have sufficient energy for the reaction.
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25
Q

Describe how a change in the base sequence of the DNA coding for an enzyme may result in a non-functional protein. [4]

A
  1. Change in primary structure changes
    sequence of amino acids;
  2. Hydrogen bonds and Ionic bonds and Disulphide bonds form in different positions;
  3. Alters the tertiary structure of the enzyme / alters shape of active site;
  4. No Enzyme-Substrate complexes can be formed;
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26
Q

What is the proteome of a cell?

A

(The proteome is the full) range of /** number of different** proteins that a cell is able to produce (at a given time);
OR
(The proteome is the full) range of / number of different proteins the genome / DNA is able to code for;

27
Q

Describe & explain how you could use the biuret test to distinguish a solution of enzyme, lactase, from a solution of lactose (2)

A
  1. Add Biuret reagent to both solutions) – no
    mark;
  2. Lactase / enzyme will give purple / lilac / mauve;
    OR
  3. Lactose / reducing sugar will not give purple /
    lilac /mauve / will remain blue;
  4. Because Lactase is a protein;
27
Q

How often should you use Brainscape?

A

A minimum of 3 times per week

28
Q

Sucrase does not hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why.(2)

A
  1. Lactose has a different shape/structure;
  2. Does not fit/bind to active site of enzyme/sucrase;
    OR
  3. Active site of enzyme/sucrase has a specific shape/structure;
  4. Does not fit/bind to lactose so no Enzyme-Substrate Complexes formed.
29
Q

Describe the induced fit model of enzyme action.(2)

A
  1. Active site not complementary;
  2. Active site changes (shape) / is flexible;
  3. (Change in enzyme allows) substrate to able to fit / Enzyme-Substrate complex to form;
30
Q

Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. (3)

A
  1. Substrate binds to the active site/enzyme OR Enzyme-substrate complex forms;
  2. Active site changes shape (slightly) so it is complementary to substrate OR Active site changes shape (slightly) so distorting/breaking/forming bonds in the substrate;
  3. Reduces activation energy;
31
Q

Describe one way that the lock and key model is different from the induced fit model.(2)

A
  1. Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around
  2. substrate / (already) fits the substrate / is
  3. complementary (before binding);
32
Q

An enzyme catalyses only one reaction. Explain why. [2]

A
  1. (Enzyme has) active site is a specific shape;
  2. Only one substrate fits / binds (the active site);
33
Q

Insulin is a protein so it cannot be taken orally. Suggest why insulin cannot be taken orally.(2)

A
  1. Broken down by enzymes / digested / denatured (by pH) /too large to be absorbed;
  2. Insulin no longer functional
34
Q

What is the effect of substrate concentration on the rate of an enzyme controlled reaction(3)

A
  1. Increases then plateaus / constant / steady / rate does not change;
  2. It plateaus as all active sites occupied / Saturated;
  3. (rate of reaction) / maximum number of Enzyme-Substrate complexes per second;
35
Q

Explain how a competitive inhibitor works (3)

A
  1. Inhibitor is a similar shape to substrate;
  2. Inhibitor enters active site / competes with substrate;
  3. Less substrate binds/fewer enzyme-substrate complexes form per second.
36
Q

Describe how a non-competitive inhibitor works [3]

A
  1. Attaches to the enzyme at a site other than the active site (allosteric site);
  2. Changes (shape of) the active site OR Changes tertiary structure (of enzyme);
  3. (So active site and substrate) no longer complementary so less/no substrate can fit/bind (‘no longer complementary so less/no enzyme-substrate complexes form’);
37
Q

What type of inhibitor can be overcome with an increase in substrate concentration?

A

Competitive

38
Q

Describe how the structure of DNA relates to its function. [6]

A
  1. Sugar-phosphate (backbone)/double stranded/helix so provides strength/stability /protects bases/protects hydrogen bonds;
  2. Long/large molecule so can store lots of information;
  3. Helix/coiled so compact;
  4. Base sequence allows information to be stored/ base sequence codes for amino acids/protein;
  5. Double stranded so replication can occur semi-conservatively/ strands can act as templates;
  6. Complementary base pairing / A-T and G-C so accurate replication/identical copies can be made;
  7. (Weak) hydrogen bonds for replication/ unzipping/strand separation;
  8. Many weak hydrogen bonds so stable/strong molecule;
39
Q

Describe the structure of DNA. [5]

A
  1. Polymer of nucleotides;
  2. Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
  3. Phosphodiester bonds (between nucleotides);
  4. Double helix/2 strands held by hydrogen bonds;
  5. (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;
40
Q

Describe Semi-conservative replication. [5]

A
  1. Strands separate / H-bonds break;
  2. DNA helicase (involved);
  3. Both strands/each strand act(s) as (a) template(s);
  4. (Free) nucleotides attach;
  5. Complementary/specific base pairing due to H bonds forming between bases/ Adenine to Thymine and GC;
  6. DNA polymerase joins nucleotides (on new strand) forming phoshodiester bonds by condensation;
  7. Semi-conservative replication / new DNA molecules contain one old strand and one new strand;
41
Q

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule. [3]

A
  1. Condensation (reaction)/loss of water;
  2. (Between) phosphate and deoxyribose;
  3. (Catalysed by) DNA polymerase;
42
Q

Describe how the separation of DNA strands occurs. [2]

A
  1. DNA helicase;
  2. Breaks hydrogen bonds between base pairs/ AT and GC/complementary bases OR Breaks hydrogen bonds between polynucleotide strands;
43
Q

Describe the role of DNA polymerase in the semi-conservative replication of DNA. [3]

A
  1. Joins (adjacent DNA) nucleotides;
  2. (Catalyses) condensation (reactions);
  3. (Catalyses formation of) phosphodiester bonds (between adjacent nucleotides);
44
Q

Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication.

A

Crick and Watson;

45
Q

Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA. [2]

A
  1. Weak / easily broken hydrogen bonds between bases allow two strands to separate / unzip;
  2. Two strands, so both can act as templates;
  3. Complementary base pairing allows accurate replication;
46
Q

State four structural differences between a DNA molecule and an mRNA molecule [4]

A
  1. DNA has deoxyribose, mRNA has ribose;
  2. DNA has thymine, mRNA has uracil;
  3. DNA longer, mRNA shorter;
  4. DNA is double stranded, mRNA is single stranded;
  5. DNA has hydrogen bonds, mRNA has no hydrogen bonds OR DNA has (complementary) base pairing, mRNA does not;
47
Q

Give two ways in which ATP is a suitable energy source for cells to use. [2]

A
  1. Releases relatively small amount of energy/ little energy is lost as heat;
  2. Releases energy instantaneously;
  3. Phosphorylates other compounds, making them more reactive;
  4. Can be rapidly re-synthesised;
  5. Is not lost from/ does not leave cells;
48
Q

Describe how an enzyme can be phosphorylated.

A
  • Attachment/association of (inorganic) phosphate (to the enzyme);
  • (Released from) hydrolysis of ATP OR (Released from) ATP to ADP + Pi;
49
Q

Explain five properties that make water important for organisms. [5]

A
  1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
  2. A solvent so (metabolic) reactions can occur OR A solvent so allowing transport of substances;
  3. High heat capacity so buffers changes in temperature;
  4. Large latent heat of vaporisation so provides a cooling effect (through evaporation);
  5. Cohesion (between water molecules) so supports columns of water (in plants);
  6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;
50
Q

State and explain the property of water that helps to prevent temperature increase in a cell. [2]

A
  1. High (specific) heat capacity;
  2. Buffers changes in temperature;
51
Q

Give two properties of water that are important in the cytoplasm of cells.

For each property of water, explain its importance in the cytoplasm.
[4]

A
  1. Polar molecule;
  2. Acts as a (universal) solvent;
    OR
  3. (Universal) solvent;
  4. (Metabolic) reactions occur faster in solution;
    OR
  5. Reactive;
  6. Takes place in hydrolysis / condensation / named reaction;
    Polar molecule so acts as (universal) solvent so (metabolic reactions are faster = 3 marks
52
Q

Describe the roles of iron ions, sodium ions, and phosphate ions in cells. [5]

A

Iron ions
1. Haemoglobin binds/associates with oxygen OR Haemoglobin transports/loads oxygen;
Sodium ions
2. Co-transport of glucose/amino acids (into cells);
3. (Because) sodium moved out by active transport/Na – K pump;
4. Creates a sodium concentration/diffusion gradient;
5. Affects osmosis/water potential;
Phosphate ions
6. Affects osmosis/water potential;
7. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
8. Used in/to produce ATP;
9. Phosphorylates other compounds (usually) making them more reactive;
10. Hydrophilic/water soluble part of phospholipid bilayer/membrane

53
Q

How Science Works

What makes a ‘Valid’ conclusion?

A
  • Large sample size SO representative
  • Long study SO can allow…. / see effect of X
  • Control used SO comparison can be made.
  • Mean & Standard Deviation shown SO significant differences can be determined.
54
Q

Evaluate questions

What are the common ‘limitations’ that you should look out for?

A
  • Small sample size so not representative;
  • Only sampled males, females may respond differently to treatment;
  • Only tested on …….. in a lab, in the wild, may obtain different pattern in data;
  • Only tested on …….. species, might not be true for all species;
  • No STATS test so differences could be due to chance;
  • Data is SUBJECTIVE, some people may have lied/ hard to determine the true end point (colour change).
55
Q

How Science Works

How do you write a ‘Null Hypothesis’?

A
  • [x] will have no effect on [y]
  • E.g. Temperature will have no effect on rate of reaction
  • There will be no correlation between age and weight
  • There will be no difference between the observed and expected ratio of 3:1 brown eyes to blue eyes
56
Q

HSW

Explain why a log scale is used to record the number of cells/bacteria.

A
  • Large range/difference/increase in numbers;
  • Accept reference to exponential (increase)
57
Q

HSW

Why do we use PERCENTAGE changes (e.g. % increase or % decrease)?

A
  • Starting values differ / allows comparison of changes over time
  • Measure the effect of X (IV)
58
Q

HSW

Why do we use RATIOS ?

A
  • Allows valid comparisons between two numbers
  • Original numbers may vary
59
Q

HSW

Why is a CONTROL needed in an investigation?

A

Shows baseline/normal value so allows comparison with other treatments.

Shows effect of x axis (independent variable)

60
Q

HSW

How do we increase RELIABILITY?

A

More data collected / larger sample size
Over longer period of time / more time points
More independent variable values tested
Anomalies have less effect

61
Q

HSW

Why do we use STANDARD DEVIATIONS?

A
  • Shows spread of data around the mean
  • Reduces the effect of outliers
  • See if differences between mean values are significant (SD don’t overlap ) or not (SD do overlap) / calculate T value for the T test
62
Q

Draw the structure of alpha glucose (1)

A

2023-25 Biology (9 decks)

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