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BIOLOGY > 1.1-1.3 : biological molecules > Flashcards

1.1-1.3 : biological molecules Flashcards

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1
Q

What is a monomer?

A

A monomer is a small identical repeating unit 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 identical 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

what is a condensation reaction?

A

joining two monomer units together with the removal of one water molecule which forms a bond

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5
Q

what is a hydrolysis reaction?

A

addition of one molcule of water to break the bond between two monomer

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6
Q

what is a disaccharide(DIMER) ?

A

TWO monosaccharides joined together in a condensation reaction

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7
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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8
Q

starch is a mixture of which two plysaccharides?

A

amylopectin and amylose

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9
Q

structure and function of amylose

A

-long unbranched chain of α-glucose
-carbon 1:4 glycosidic bonds provide a coiled structure
-compact so is good for storage
-insoluble so doesn’t affect water potential
-large so doesn’t diffuse out of cells

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10
Q

structure and function of amylopectin

A

-branched chain of α-glucose
-carbon 1:4 and 1:6 glycosidic bonds
-provides LSA for for rapid hydrolysis by
enzymes to release glucose for respiration
-insoluble so doesn’t affect water potential
-large so doesn’t diffuse out of cell

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11
Q

give three examples of monosaccharides

A

glucose
fructose
galactose

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12
Q

three examples of disaccharides

A

sucrose
maltose
lactose

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13
Q

give two types of polysaccharides

A

storage (glycogen and starch)
structural (cellulose)

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14
Q

give the structure and function of glycogen?

A

ONLY FOUND IN ANIMAL CELLS
-short chains so is more rapidly hydrolysed into glucose used in RESPIRATION
-more highly branched
-larger SA
-insoluble so does not affect water potential

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15
Q

Where is glycogen stored?

A

muscles and liver

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16
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

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17
Q

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

A

-Both polysaccharides / Both are made of glucose monomers;
-Both contain glycosidic bonds (between monomers);
-Both contain carbon, hydrogen and oxygen/C, H and O;
-Starch has α-glucose and cellulose has β-glucose;
-Starch (molecule) is helical/coiled and cellulose (molecule) is straight;
-Starch (molecule) is branched and cellulose is not/unbranched;
-Cellulose has (micro/macro) fibrils and starch does not;
-Starch has 1–6 glycosidic bonds and cellulose does not
OR Starch contains two types of molecule and cellulose contains one type of molecule

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18
Q

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

A

-Helical So compact / tightly packed
-Insoluble So no osmotic effect / does not leave cell / does not affect water potential;
-Large molecule So does not leave cell
-Branched chains So rapid hydrolysis to remove glucose for respiration;

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19
Q

Hydrogen bonds are important in cellulose molecules. Explain why.

A

-Holds chains/cellulose molecules together/forms cross links between chains/forms microfibrils;
-Providing strength/rigidity
-Weak Hydrogen bonds provide strength in large numbers;

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20
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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21
Q

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

A

Glucose and fructose
Joined by condensation
Joined by glycosidic bond
Added to polypeptide in Golgi

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22
Q

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

A

Add Benedict’s;
Heat to 95°C;
Red/orange/yellow/green precipitate (shows reducing sugar present);

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23
Q

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

A

Add potassium iodide (KI) solution to the food sample;
Blue/black/purple indicates starch is present;

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24
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

(Mix / shake sample) with ethanol, then water and shake;
Cloudy White / milky (emulsion);

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25
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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26
Q

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

A

Crush/grind;
With ethanol/ alcohol, to dissolve the lipid;
Then add water then shake;
Forms a white emulsion / goes white;

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27
Q

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

A

Condensation (reaction) OR Loss of water;
Between of glycerol and fatty acid;

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28
Q

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

A

Fatty acid removed;
Replaced with a phosphate group;

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29
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.

30
Q

Describe the biochemical tests you would use to confirm the presence of non-reducing sugar

A

-Do Benedict’s test and stays blue/negative;
-Boil with acid then neutralise with alkali;
-Heat with Benedict’s and becomes red/orange (precipitate);

31
Q

describe how you would produce a calibration curve for a reducing sugar of unknown concentration and use it to obtain results.

A

-make up several known concentrations of maltose/glucose/lactose/galactose/fructose
-carry out the benedict’s test on each sample
-use a colorimeter to measure the colour intensity of each solution and plot a calibration curve
-known conc.on X axis and transmission on Y
-find the conc of the known sample using the calibration curve

32
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

Filter and dry (the precipitate);
Find mass/weight;

33
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;

34
Q

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

A

-Structure is determined by (relative) position of amino acid/R group
-Primary structure is sequence/order of amino acids;
-Secondary structure formed by hydrogen bonding (between amino acids);
Accept alpha helix/β-pleated sheet for ‘secondary structure’
-Tertiary structure formed by interactions (between R groups);
-Creates active site in enzymes
-Quaternary structure contains >1 polypeptide chain OR Quaternary structure formed by interactions/bonds between polypeptides;

35
Q

name and explain the 3 different types of bonds between R groups

A

1- WEAK hydrogen bonds between C=O and NH of the adjacent amino acid
2-IONIC BONDs between oppositely charged R groups
-DISULPHIDE BRIDGES between cysteine amino acids( has sulfur)

36
Q

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

A

Condensation (reaction) / loss of water;
Between amine / NH2 and carboxyl / COOH;

37
Q

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

A

-Condensation reaction between amino acids;
-(Forming) peptide bonds;
-Creating (specific) sequence/order of amino acids;

38
Q

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

A

-Reduces activation energy
-Due to bending bonds OR Without the enzyme, very few substrates have sufficient energy for the reaction.

39
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

-Change in primary structure changes
sequence of amino acids;
-Hydrogen bonds and Ionic bonds and –Disulphide bonds form in different positions;
-Alters the tertiary structure of the enzyme / alters shape of active site;
- No Enzyme-Substrate complexes can be formed;

40
Q

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

A

-Add Biuret reagent to both solutions
-Lactase / enzyme will give purple OR
-Lactose / reducing sugar will remain blue;
-Because Lactase is a protein;

41
Q

What is the proteome of a cell?

A

number of different proteins the genome / DNA is able to code for;

42
Q

what is activation energy?

A

the minimum energy required for a successful chemical reaction

43
Q

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

A

-Active site not complementary;
-Active site changes (shape) / is flexible;
-(Change in enzyme allows) substrate to able to fit / Enzyme-Substrate complex to form;

44
Q

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

A

-Substrate binds to the active site
-Active site changes shape (slightly) so distorting/breaking/forming bonds in the substrate;
-Reduces activation energy;

45
Q

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

A

-Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around
-substrate / (already) fits the substrate / is
-complementary (before binding);

46
Q

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

A

-(Enzyme has) active site is a specific shape;
-Only one substrate fits / binds (the active site);

47
Q

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

A

-Broken down by enzymes / digested / denatured (by pH) /too large to be absorbed;
-Insulin no longer functional

48
Q

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

A

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

49
Q

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

A

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

50
Q

Explain how a competitive inhibitor works (3)

A

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

51
Q

Describe how a non-competitive inhibitor works [3]

A

-Attaches to the enzyme at a site other than the active site (allosteric site);
-Changes (shape of) the active site OR Changes tertiary structure (of enzyme);
-(So active site and substrate) no longer complementary so less/no enzyme-substrate complexes form

52
Q

Describe the effect of temperature on enzyme action

A

-increasing the temperature increases the KE of molecules
-so more likely to sucessfully collide and react
-more enzyme-substrate complexes from per second

-beyond optimum: atoms vibrate faster
-this causes weak hydrogen and ionic bonds to break which causes a change in the tertiary structure
-active site is no longer complementary to the substrate
-enzyme is DENATURED( no ES complexes can form)

53
Q

Describe the effect of pH on enzyme action

A

pH is the measure of H+ concentration so if pH is changed from optimum then
- the charg eon the R groups of the amino acids is altered
-ionic bonds in the tertiary structure are broken
-active site changes shape
-less E-S complexes form so enzyme denatures

54
Q

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

A
  • Sugar-phosphate (backbone) so provides strength
    -Long/large molecule so can store lots of information;
    -Helix/coiled so compact;
    -Base sequence codes for amino acids/protein;
    -Double stranded so replication can occur semi-conservatively
    -Complementary base pairing so accurate replication
    -(Weak) hydrogen bonds for replication/ unzipping
    -Many weak hydrogen bonds so stable/strong molecule;
55
Q

Describe the structure of DNA. [5]

A
  • Polymer of nucleotides;
  • Each nucleotide formed from deoxyribose, a phosphate (group) and an nitrogenous base;
  • Phosphodiester bonds (between nucleotides);
  • Double helix held by hydrogen bonds;
  • (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;
56
Q

Describe Semi-conservative replication. [5]

A
  • Strands separate / H-bonds break;
  • DNA helicase (involved);
  • Both strands act(s) as (a) template(s);
  • (Free) nucleotides attach;
  • Complementary base pairing due to H bonds forming between bases
  • DNA polymerase joins nucleotides (on new strand) forming phoshodiester bonds by condensation;
  • new DNA molecules contain one old strand and one new strand;
57
Q

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

A

-Condensation (reaction)/loss of water;
-(Between) phosphate and deoxyribose;
-(Catalysed by) DNA polymerase;

58
Q

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

A

Crick and Watson

59
Q

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

A

-Weak hydrogen bonds between bases allow two strands to separate
- two strands so both act as templates;
-Complementary base pairing allows accurate replication;

60
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

61
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;

62
Q

give 2 ways in which the hydrolysis of ATP is used in cells(2)

A

1- PROVIDES ENERGY FOR:
active transport
muscle contraction
protein synthesis
2- PHOSPHOYLATION:
of molecules to lover Ea
make substrate more reactive

63
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;
64
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
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;

65
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
  • Polar molecule;
  • Acts as a (universal) solvent;
  • (Metabolic) reactions occur faster in solution;
  • Reactive;
    Takes place in hydrolysis / condensation reaction;
66
Q

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

A

Iron ions
1. Haemoglobin binds/associates with 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

67
Q

describe how ATP is resynthesised in cells(2)

A

1- ADP + Pi
2- by ATP synthase
3- in respiration

68
Q

contrast the structures of ATP and a nucleotide found in DNA to give TWO differences(2)

A
  • ATP has ribose and DNA has deoxyribose
  • ATP has 3 phosphate groups and DNA has 1
  • ATP base is always adenine and in DNA it can be different
69
Q

suggest why water becomes lighter as it expands(2)

A
  • density=mass/volume
  • ice has same mass of water but greater volume
70
Q

suggest one biological advantage of water becoming lighter (2)

A
  • ice is colder than water
  • is lighter so ice floats on water
    -reduces freezing of water below ice
71
Q

Explain why water is considered so important for life to ocuur (6)

A
  • life evolved in water
  • water provides support for bodies of oragnisms
  • water is a major component of cytoplasm
  • water is a universal solvent
  • water is a metabolite
  • water stabilises external temperatures

BIOLOGY (13 decks)

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