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Biology > Topic 1: Biological Molecules > Flashcards

Topic 1: Biological Molecules Flashcards

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1
Q

What is a biological molecule?

A

A group of chemicals found in living organisms.

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2
Q

What is an organic molecule?
How does this link to evolution?

A

A molecule containing carbon.
Carbon atoms readily bond with other carbon atoms, forming a backbone for molecules. All life on Earth is based on carbon (shares a similar chemistry), which is indirect evidence for evolution.

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3
Q

What are the 3 main ways atoms bond together? Explain them

A
  • Covalent bonding - atoms share a pair of electrons in their outer shell = a more stable molecule
  • Ionic bonding - ions with opposite charges attract, the electrostatic attraction is the bond, weaker than covalent bonds
  • Hydrogen bonding - polar molecules (electrons in a molecule aren’t evenly distributed so some regions are charged) form a weak electrostatic bond between the + and - regions. Collectively can alter physical properties.
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4
Q

What is a monomer?

A

A molecule that can be joined to other identical molecules to form a polymer.

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5
Q

What is a polymer?

A

A macromolecule made from long chains of repeating sub-units (monomers).

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6
Q

What is polymerisation?

A

The process by which monomers are joined to form a polymer.

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7
Q

What is a condensation reaction?

A

Monomers join to form polymers, releasing a molecule of water for each new sub-unit added.

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8
Q

What is a hydrolysis reaction?

A

Water molecules are used to break the bonds linking monomers to break down a polymer.

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9
Q

What is a molar solution?

A

A solution that contains one mole of solute per litre of solution.

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10
Q

What is metabolism?

A

A collective name for all the chemical processes that take place in living organisms.

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11
Q

What 4 carbon-based compounds are all living organisms made from?

A
  • Carbohydrates
  • Proteins
  • Lipids
  • Nucleic acids
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12
Q

What are the monomers that make up the 4 biological polymers that organisms are made from?

A
  • Carbohydrates - monosaccharides form polysaccharides
  • Proteins - amino acids form polypeptides
  • Nucleic acids - nucleotides form polynucleotides
  • Lipids do not form polymers
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13
Q

What 4 elements are most biological polymers based on?

A
  • Carbon
  • Hydrogen
  • Nitrogen
  • Oxygen
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14
Q

What elements are carbohydrates made from?
What are their main functions?

A

Carbon, Hydrogen, Oxygen in a 1:2:1 ratio
Energy storage and structural support (e.g plant cell walls)

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15
Q

What is a monosaccharide?
What is the general formula?
Name three examples
What is their formula?

A

A single monomer of a carbohydrate
(CH20)n where n is between 3 and 7
Glucose (alpha/beta), Fructose, Galactose
All have C6H12O6 - six carbon atoms so are hexoseS

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16
Q

What is an isomer?

A

Molecules with the same general formula but differ structurally

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17
Q

What are the two isomers of glucose?

Where are their reducing centres?

A

alpha glucose - the two hydroxyl groups are both on the bottom
beta glucose - the two two hydroxyl groups are on opposite sides

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Carbon 1’

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18
Q

What is the test for reducing sugars?

A
  • Add 2cm^3 of food sample to 2cm^3 of Benedict’s reagent
  • Heat mixture in a boiling water bath for 5mins
  • The blue solution forms a brick red precipitate (can be green, yellow etc depending on sugar concentration)
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19
Q

Explain the test for reducing sugars

A
  • Reducing sugars donate electrons from their reducing centres to blue copper (II) sulphate (Benedict’s reagent)
  • Copper (I) oxide forms - a brick red precipitate
  • The reducing sugar is oxidised, Benedict’s reagent is reduced
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20
Q

What is a reducing sugar?

A

A sugar that can reduce (donate electrons to) another chemical. Includes all monosaccharides and the disaccharides maltose and lactose

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21
Q

What is a disaccharide?
Name three disaccharides and what monosaccharides they are made from

A

Two monosaccharides joined together
glucose + glucose = maltose
glucose + fructose = sucrose
glucose + galactose = lactose

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22
Q

How do monosaccharides join?
How are disaccharides broken down?

A

They join by condensation reactions, giving out a molecule of water, forming a glycosidic bond
A water molecule is added, breaking the glycosidic bond and releasing the constituent monosaccharides in a hydrolysis reaction

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23
Q

What is the test for non-reducing sugars?

A
  • Test for reducing sugars (only continue if the result is negative)
  • Add a new 2cm^3 sample to2cm^3 HCl and put the solution in a boiling water bath fo 5mins
  • Add sodium hydrogencarbonate solution to neutralise HCl. Test with pH paper to ensure the conditions are alkaline
  • Re-test for reducing sugars, a positive result means non-reducing sugars are present
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24
Q

Explain the test for non-reducing sugars

A

Boiling the sample with HCl will hydrolyse any disaccharides into their constituent monosaccharides , which are reducing sugars. Sodium hydrogencarbonate is needed to neutralise the acid because Benedict’s reagent doesn’t work in acidic conditions.

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25
Q

What are polysaccharides?
Give three examples

A

Polymers made from many monosaccharides joined by glycosidic bonds formed by condensation reactions. When hydrolysed, they break down into disaccharides or monosaccharides.

Starch, glycogen, cellulose

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26
Q

What is the test for starch?

A

Add two drops of iodine solution to 2cm^3 of food sample. A positive result will turn from yellow to blue-black

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27
Q

Where is starch usually found?

A

Not found in animal cells. Usually stored as intracellular starch grains, especially in seeds.

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28
Q

Describe the structure of starch.

A

Made from chains of alpha glucose monosaccharides.

  • Amylose chains = unbranched with 1-4 glycosidic bonds. Wound in a helix that makes the molecule compact. Hydroxyl groups pointing inwards form hydrogen bonds that hold the helix in place
  • Amylopectin chains = branched with 1-6 glycosidic bonds at side branches
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29
Q

What makes starch suitable for energy storage?

A
  • Insoluble = doesn’t affect water potential so water not drawn in by osmosis
  • Large + insoluble = doesn’t diffuse out cells
  • Compact = a lot stored in a small space
  • Forms alpha glucose when hydrolysed = easily transported + readily used in respiration
  • Branches = many ends = acted on by enzymes simultaneously = glucose released rapidly
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30
Q

Where is glycogen found?

A

Animals and bacteria (never plants), stored in small granules in muscles and the liver (although fat is the main storage molecule in animals)

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31
Q

Describe the structure of glycogen

A

Similar to starch but more highly branched with shorter chains

  • Made from chains of alpha glucose with 1-4 and 1-6 (at side branches) glycosidic bonds
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32
Q

Why is glycogen suitable for storage?

A
  • Insoluble = doesn’t draw water into cells by osmosis
  • Insoluble = doesn’t diffuse out cells
  • Compact = lots stored in a small space (good for mobile animals)
  • More highly branched = more ends acted on by enzymes simultaneously = more rapidly broken down into glucose for respiration ( animals have higher metabolic + respiratory rate than plants because more active)
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33
Q

Where is cellulose found?

A

In plant cell walls as a rigid structural molecule

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34
Q

Describe the structure of cellulose

A

Monomers of beta glucose form straight, unbranched chains.
Hydrogen bonds between adjacent parallel chains strengthen substance.
Adjacent beta-glucose molecules rotate 180 degrees so hydroxyl groups can form hydrogen bonds.
Grouped into microfibrils which are arranged into parallel fibrils.

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35
Q

What are the functions of cellulose?

A
  • Provides rigidity to plant cells
  • Stops cells bursting as water enters by osmosis by exerting an inward pressure, stopping further influx of water
  • Makes plant cells turgid + push against each other, making non-woody parts of the plant semi-rigid
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36
Q

Why is cellulose suitable for structure and rigidity?

A
  • Made from beta-glucose molecules = form long, straight unbranched chains
  • Molecular chains run parallel + are cross-linked by hydrogen bonds, adding collective strength
  • Molecules grouped into microfibrils, which are grouped into fibres, adding more strength
  • Microfibrils permeable to water as cells need it for metabolic reactions
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37
Q

What elements do lipids contain?
In what proportions?
Comment on their solubility

A

Carbon, hydrogen, oxygen
Proportion of O to C and H is smaller than carbohydrates
Insoluble to water but soluble in organic solvent solvents (e.g alchohols, acetone)

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38
Q

What are the functions of lipids?

A
  • Cell membranes - phospholipids contribute to flexibility + transfer of lipid-soluble substances
  • Energy source - provide over 2x energy as the same mass of carbohydrate, and provide water
  • Waterproofing - insoluble in water so form waxy, lipid cuticles to conserve water OR an oily secretion (sebum) in mammals
  • Insulation - slow conductors so stored beneath surface to retain body heat + around nerve cells (electrical insulators)
  • Protection - often stored around delicate organs
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39
Q

What is the difference between fats and oils?

A

Fats are solid at room temperature, oils are liquid

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40
Q

Describe the test for lipids

A
  • Put 2cm^3 of food sample and 5cm^3 of ethanol in a completely dry test tube
  • Shake thoroughly to dissolve lipid
  • Add 5cm^3 of water and shake gently
  • Positive result = milky white emulsion (because lipid droplets dispersed finely)
  • As a control, repeat with just water, should remain clear
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41
Q

Describe the structure of a triglyceride

A

3 fatty acids form ester bonds with glycerol in a condensation reaction (hydrolysis = inverse)
Differences in properties come from variations in the fatty acids:
All have a carboxyl group + a hydrocarbon chain

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42
Q

Describe the hydrocarbon chains in fatty acids (in reference to triglycerides)

A

Can be saturated (C atoms linked to the maximum possible number of H), mono-unsaturated (one C=C) or poly-unsaturated (many C=C)
Double bonds cause the molecule to bend = can’t pack together closely = liquid at room temp

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43
Q

How are the structures of triglycerides related to their properties?

A
  • High ratio of energy-storing C-H bonds to C atoms = excellent source of energy
  • Low mass : energy ratio = lots of energy in a small volume = good storage molecule for mobile animals (less mass)
  • Large + non-polar = insoluble in water = doesn’t affect osmosis or water potential of cells
  • High ratio of H:C atoms = release water when oxidised = source of water
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44
Q

What are the two types of lipid?

A

Triglycerides
Phospholipids

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45
Q

Describe the structure of phospholipids

A

One glycerol, two fatty acids and a phosphate molecule form ester bonds in a condensation reaction.

They are polar molecules (two ends behave differently). They have a polar head (phosphate molecules are hydrophilic - attract water and don’t mix with fat) and a non-polar tail (fatty acids are hydrophobic - repel water and mix with fat)

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46
Q

How do phospholipid molecules behave in water?

A

Because they are polar molecules, they position themselves so the hydrophilic heads are as close to water as possible, with the hydrophobic tails as far away as possible

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47
Q

Describe how phospholipids’ structure relate to their properties

A
  • Polar molecules = in aqueous environments, phospholipids form a bilayer within cell-surface membranes = a hydrophobic barrier is formed between the inside/outside of a cell
  • Hydrophilic phosphate heads help to hold at the surface of the cell-surface membrane
  • Phospholipid structure lets them form glycolipids by combining with carbohydrates within the cell-surface membrane. Important in cell recognition
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48
Q

What is a protein?

A

Usually very large molecules but there are many types. Amino acids are the monomer units that combine to make a polymer called a polypeptide. These can combine to make proteins.

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49
Q

How many amino acids occur naturally?
What shape are they?

A

20
Individual amino acids have a tetrahedral shape due to the angles of the bonds

50
Q

What is a dipeptide?

A

Two amino acids joined by a peptide bond (between N and C) by a condensation reaction.

51
Q

What is the general structure of an amino acid?

What atoms react to form the water molecule in a condensation reaction?

A

H R O
\ | //
N - C - C
/ | \
H H O-H

NH2 = amino group
R = variable group
COOH = carboxyl group

The OH from the carboxyl group and a H from the amino group of another acid

52
Q

What is the general structure of a dipeptide?
Where is the peptide bond?

A

H R1 H R2 O
\ | | | //
N - C - C – N - C - C
/ | || | \
H H O H O-H

C=O = carbonyl group
peptide bond = C–N

53
Q

Describe the test for proteins

A
  • Add equal volumes of the food sample and Biuret’s reagent
  • Positive result = turns from blue to purple
54
Q

Describe the primary structure of a protein

A
  • Many amino acids join by a series of condensation reactions to form polypeptides (polymerisation).
  • Primary structure is the sequence of amino acids (determined by DNA)
  • Primary structure determines its shape (specific to function)
  • A change in 1 amino acid can change the shape (+ function)
55
Q

Describe the secondary structure of a protein

A

Hydrogen bonding (between the electronegative oxygen of carbonyl groups and the slightly positive hydrogen of NH groups) of the peptide backbone folds amino acids into a repeating structure

Can be an alpha-helix or beta-pleated sheet

56
Q

Describe the tertiary structure of a protein

A
  • Secondary protein structure is twisted and folded further into a 3D pattern due to side chain interactions.
  • Maintained by disulfide bridges, ionic bonds and hydrogen bonds
  • 3D shape is important to function (so the protein is distinctive + recognisable to other molecules)
  • All globular proteins display tertiary structure
57
Q

Describe the bonds involved in the tertiary structure of a protein

A
  • Disulfide bridges - strong + not easily broken
  • Ionic bonds - between the carboxyl + amino groups not involved in peptide bonds, easily broken by pH changes
  • Hydrogen bonds - numerous but easily broken
58
Q

Describe the quaternary structure of a protein

A

Large proteins made from multiple polypeptide chains ( and non-protein / prosthetic groups) combined and held together by bonds. While 3D structure is important to function, primary structure determines the shape in the first place

59
Q

What is a globular protein?

A

A protein with a roughly spherical shape, mostly used for metabolic functions

60
Q

What is a fibrous protein? Give an example

A

A protein made from long chains, mostly used for structural functions
Collagen

61
Q

What is an enzyme?

How much of them do you need for them to be effective and why?

A

Globular protein that is reaction specific and acts as a biological catalyst (alters the rate of reaction without undergoing permanent change).

Can be used repeatedly so are effective in small amounts

62
Q

What are three conditions needed for a typical reaction to occur?

A

-Reactants collide with enough energy to alter the arrangement of atoms
- Free energy of the products must be less than the substrates
- Must have the activation energy

63
Q

What is free energy?
What is activation energy?

A
  • Energy of a system available to perform work
  • Minimum amount of energy needed to start a reaction
64
Q

How do enzymes affect the temperature at which a reaction can occur?
Why is this important?

A
  • Lower the activation energy of a reaction so it can occur at a lower temperature
  • Allows metabolic reactions to occur at body temp which would otherwise be too slow to sustain life
65
Q

What is an anabolic reaction?
What is a catabolic reaction?

A
  • Enzymes bring substrate molecules together
  • Enzyme’s active site affects bonds in the substrate so they are easier to break
66
Q

Describe the structure of an enzyme

A

Globular proteins at the tertiary structure, have a specific 3D shape which is a result of their sequence of amino acids (primary structure)

Have an active site - functional region of the enzyme that the substrate binds to, made from a relatively small number of amino acids. Forms a small depression in the large molecule

67
Q

Describe what happens at the active site of an enzyme during a reaction

A

Active site has a shape complementary to the substrate (molecule that the enzyme acts on).
Certain amino acids in the active site temporarily bond to the substrate, forming an enzyme-substrate complex

68
Q

What are the two models of enzyme action?
Which one is more widely accepted?

A

Lock and Key and Induced Fit

Induced Fit

69
Q

Describe the Lock and Key model of enzyme action

What is the limitation?-

A
  • Substrate and enzyme shapes fit exactly, enzyme is considered a rigid structure
  • Suggests enzymes are rigid when they are flexible (molecules can bind to sites other than the active site which alters its shape)
70
Q

Describe the Induced Fit model of enzyme action

What are its advantages?

A
  • Proximity of the substrate changes the shape of the active site to mould around it
  • As it changes shape, it puts strain on the substrate’s bonds, reducing the activation energy needed to break it. Any change in the enzyme’s environment can change its shape
  • Enzyme-substrate complex forms and substrate is converted into products
  • When product leaves enzyme, active site returns to original shape
  • Shows how enzyme activity can be altered by other molecules (e.g inhibitors)
  • Shows how activation energy is lowered
71
Q

What are the two conditions needed for an enzyme to work?

A
  • Must have an active site complementary to the substrate
  • Must come into physical contact with the substrate
72
Q

What are the two ways of measuring an enzyme-catalysed reaction?
Describe their graphs

A
  • Rate of formation of product (upward curve on graph before it levels off)
  • Rate of disappearance of substrate (downwards curve on graph before it levels off)
73
Q

Explain the graphs for an enzyme-catalysed reaction (formation of product/disappearance of substrate)

A
  • At first, lots of substrate but no product
  • Collisions between substrate + enzyme molecules frequent
  • All active sites occupied at once = substrate broken down rapidly
  • As reaction continues less substrate and more product
  • More difficult for contact between substrate + enzyme as there is less substrate + product molecules get in the way = slower rate
  • Rate continues to slow until so little substrate present that concentration can’t be measured
  • Reaction stops when all the substrate is used up
74
Q

What 5 factors can affect enzyme action?

A
  • Temperature
  • pH
  • Enzyme concentration
  • Substrate concentration
  • Presence of inhibitors
75
Q

Describe the effect of temperature on enzyme action

A
  • As temp increases, so does kinetic energy = molecules move quicker = more frequent collisions with more force. More enzyme-substrate complexes = quicker rate.
  • Optimum temp for that enzyme = fastest rate
  • After optimum temp, temp increases make atoms vibrate, breaking hydrogen, ionic + disulphide bonds in the enzyme, changing its shape. Substrate doesn’t fit as well = lower rate
  • Denatured - at extreme temps, enzyme changes shape so much it no longer works (permanent change)
76
Q

Why is body temperature 37 degrees C even though most enzymes have an optimum temperature of 40?

A
  • Despite a higher metabolic rate, too much additional food would be needed to maintain 40
  • Other proteins may be denatured at higher temperatures
  • Any further increase in temperature (e.g illness) could denature the enzymes
77
Q

Describe the effect of pH on enzyme action

A

All enzymes have an optimum pH, any changes reduce its rate, extreme changes denature the enzyme because:
- Change in H+ ion concentration alters charges on amino acids in the active site, so substrate can no longer bind + enzyme-substrate complex can’t be formed
- Significant changes could break hydrogen + ionic bonds maintaining the tertiary structure, changing the shape of the active site

78
Q

Describe the effect of enzyme concentration on enzyme activity

A
  • Low enzyme conc + rate- substrate in excess = not all substrates in an active site. Increase in enzyme concentration = proportional increase in rate (more active sites available)
  • Max rate - all substrate molecules occupy an active site at once
  • Very high enzyme conc - enzyme conc exceeds substrate (substrate is limiting factor) so further increase of enzymes has no effect as all substrate molecules already fill an active site
79
Q

Describe the effect of substrate concentration on enzyme action

A
  • Low substrate conc + rate - too few substrate molecules to occupy all active sites. As substrate concentration increases, rate increases proportionally
  • Max rate (Vmax) - all active sites occupied by substrate
  • When substrate is in excess, further increase in substrate has no effect as all active sites are full
80
Q

What is an enzyme inhibitor?

A

A substance that directly or indirectly alters the active site of an enzyme, reducing its activity

81
Q

What are the two types of enzyme inhibitor?

A
  • Permanent inhibitors - inhibitor binds so strongly to the enzyme that it can never be removed
  • Reversible inhibitors - most inhibitors only bind temporarily
82
Q

What are the two types of reversible enzyme inhibitors?

A
  • Competitive inhibitors
  • Non-competitive inhibitors
83
Q

Describe how competitive enzyme inhibitors work

A
  • Have a molecular shape similar to the substrate so can occupy the active site
  • Compete with substrate for available active sites
  • The difference in concentrations of inhibitor and substrate determines its effect (determines the likelihood of the next molecule to bind to the active site being a substrate molecule)
  • Eventually all substrate molecules will occupy an active site. Time taken depends on inhibitor concentration
84
Q

Describe how non-competitive inhibitors work
What effect does the inhibitor/substrate concentration have?

A
  • Bind to the enzyme at a site other than the active site (so don’t need to resemble its shape)
  • Alter the shape of the active site so it is no longer complementary to the substrate and no enzyme-substrate complexes can form
  • Increasing substrate concentration has no effect as they aren’t competing for the same site
85
Q

Describe end-product inhibition

A

A chemical that needs to be kept at a constant concentration often inhibits an enzyme at the start of the reaction that produces it
If its concentration increases, more of it is available to inhibit the enzyme, producing less of it and decreasing its concentration.

86
Q

What are nucleic acids?

Give 2 examples

A

Polynucleotides (polymers made from nucleotide monomers).

DNA and RNA are important information-carrying molecules

87
Q

What is the structure of a nucleotide?

A
  • A pentose sugar (5 carbon atoms)
  • Phosphate group
  • Nitrogenous organic base (Adenine, Guanine, Cytosine, Thymine, Uracil)

The base and the phosphate group both attach to the pentose sugar

88
Q

How are polynucleotides formed?

A

Condensation reactions between the phosphate group of one nucleotide and the pentose sugar of another forms a phosphodiester bond.

Forms dinucleotides and polynucleotides

89
Q

What is the full name and structure of RNA?

A

Ribonucleic acid

A single, relatively short polynucleotide chain
The pentose sugar is ribose and the organic bases are adenine, guanine, cytosine and uracil

90
Q

What are the functions of RNA?

A
  • One type transfers genetic information from DNA to the ribosomes
  • Ribosomes are made from proteins and another type of RNA
  • A third type of RNA is involved in protein synthesis
91
Q

What is the full name of DNA and what is the structure of one of its nucleotides?

A

Deoxyribonucleic acid

The pentose sugar is deoxyribose
The organic bases are guanine, cytosine, adenine and thymine

92
Q

How are the polynucleotide strands arranged in DNA?

A

Made from two very long polynucleotide strands joined by hydrogen bonds between complementary base pairs
Strands are antiparallel (run in different directions) and arranged in a double helix
Strands have a structural phosphate-deoxyribose backbone

93
Q

Describe base pairing in DNA

A

Always specific - A with T (U in RNA) and G with C
The base pairs are complementary
SO quantities of A and T (and G and C) are equal. Ratio between two pairs varies between species
3 hydrogen bonds form between G and C but only 2 between A and T

94
Q

Describe the stability of DNA

A

Very stable molecule

  • Phosphodiester backbone protects more chemically reactive organic bases inside the double helix
  • Base stacking (other interactive forces between base pairs) hold the molecule together
  • Stability varies within molecule as G-C pairings have 3 H-bonds but A-T has 2. Higher proportion of G-C means a more stable molecule
95
Q

What is the function of DNA?

A
  • The hereditary material responsible for passing genetic information between cells and generations
  • Billions of base pairs in the DNA of a typical mammal = almost infinite variety of sequences = genetic diversity
96
Q

How is DNA arranged in a cell?

A
  • DNA coils around histones (proteins) to form chromosomes
  • Chromosomes found in the nucleus of the cell
  • Humans usually have 46 chromosomes (23 pairs)
97
Q

How do the properties of DNA relate to its function?

A
  • Very stable = passes from generation to generation without significant change (mutations are repaired so are rare)
  • Strands only joined by hydrogen bonds = allows them to separate in DNA replication + protein synthesis
  • Very large molecule = carries huge amount of genetic information
  • Base pairs within helical cylinder of deoxyribose-phosphate backbone = genetic information protected from corruption by outside chemical/physical forces
  • Base pairing = DNA can replicate + transfer information as mRNA
98
Q

What did scientists previously think was the hereditary material? Why?

A

Thought it was proteins due to their chemical diversity.
Thought DNA had too few components with a too simple structure

99
Q

Describe the experiment that proved that DNA is the hereditary material

A
  • Injected mouse with living safe bacterium that doesn’t cause pneumonia + dead harmful form that does - mouse developed pneumonia
  • Only explanation was that dead bacterium had information on how to make the toxin but not the means, and the safe form had means but not info
  • Substances from dead bacteria were isolated and added to the safe form. Only the DNA let it produce the toxin, so must be hereditary material
  • When enzymes that break down DNA were added, it stopped producing the toxin
100
Q

Where do new cells come from?
How does it happen?
Why must DNA replicate?

A

Apart from zygotes, all cells in multicellular organisms made from existing cells by cell division.

First nuclear division (mitosis/meiosis) then cytokinesis (whole cell divides)

Must replicate before nuclear division so all new cells have all genetic information to produce the proteins they need

101
Q

By what method does DNA replicate?
What conditions need to be met for this to occur?

A

Semi-conservative replication

  • A pool of the 4 nucleotides present (free nucleotides)
  • Both strands of DNA being copied as a template
  • The enzymes DNA helicase and DNA polymerase are present
  • A source of chemical energy (ATP) to drive the process
102
Q

What is semi-conservative replication?

A

DNA helix unwinds so each new DNA molecule contains one original polynucleotide strand used as a template and one new strand. Contains half original DNA and half new

103
Q

Describe the process of semi-conservative DNA replication

A

1) Enzyme DNA helicase breaks H bonds between nitrogenous bases, separates double helix + unwinds into 2 strands
2) Hydrolysis of ATP activates free nucleotides in nucleus
3) Each exposed polynucleotide strand acts as a template to which complementary free nucleotides attach
4) Nucleotides joined in condensation reactions by enzyme DNA polymerase to form new polynucleotide strand
5) ‘Proof-reading’ enzyme checks for mutations + a ‘winding’ enzyme winds polynucleotides into 2 DNA double helices
6) 2 daughter DNA molecules are genetically identical + contain half original, half new DNA

104
Q

What is special about the way that DNA polymerase works?

A

DNA strands are antiparallel - one is 3’ to 5’ (based on carbon numbers in deoxyribose) other is 5’ to 3’.
Active site of DNA polymerase only complementary to 3’ end so nucleotides can only be added to the 3’ end
New strand is made in a 5’ to 3’ direction so DNA polymerase enzymes on each strand work in opposite directions

105
Q

Who discovered DNA structure?
What model of DNA replication did they propose?
What other theories were there?

A

Watson and Crick with the help of Rosalind Franklin
Proposed the semi-conservative model

  • Conservative model = original molecule stays intact + a separate daughter molecule built from scratch
  • Dispersive model = new molecule is half new, half original but original/new nucleotides are scattered throughout molecule (no strand stays intact)
106
Q

Describe the experiment that proved semi-conservative replication

A

Meselson and Stahl
1) Grew bacteria (because they replicate quickly) in a growth medium with the heavy isotope of nitrogen (15N) until all their DNA had incorporated 15N

2) Centrifuged bacteria to isolate DNA and 100% formed a band lower in the tube (more dense area)

3) Grew bacteria in 14N (light isotope) for 1 generation. After centrifugation, 100% DNA is hybrid (middle band). Disproved conservative model (would have 50% heavy, 50% light)

4) After 2nd generation, 50% formed a band at 14N and 50% was hybrid. Disproved dispersive (would have 100% hybrid)

So semi-conservative is the only valid model

107
Q

What is the full name and structure of ATP?

A

Adenosine Triphosphate
A phosphorylated macromolecule made from adenine (nitrogenous base), a ribose sugar and 3 phosphate groups

The adenine and the three phosphate groups attach to the ribose with high energy bonds (are unstable = low activation energy = easily broken)

108
Q

What is the function of ATP?

A

A short-term (immediate) energy source - holds a convenient amount of energy to do work in the cell which is released when it is broken down

109
Q

Why is ATP a better immediate energy source than glucose?

A
  • Releases less energy = more manageable + less is wasted as heat
  • Hydrolysis of ATP is a single reaction = very quick release, breakdown of glucose requires several reactions = slower
110
Q

Describe the hydrolysis of ATP
Give the equation

A

An exergonic reaction catalysed by the ATP hydrolase enzyme to release energy. It is reversible

ATP + H20 -> ADP + Pi + E

ADP = adenosine diphosphate
Pi = inorganic phosphate
E = energy

111
Q

Describe the synthesis of ATP
Give the equation

A

An endergonic condensation reaction (phosphorylation) catalysed by the enzyme ATP synthase. Uses energy supplied by respiration

ADP + Pi -> ATP + H20

ADP = adenosine diphosphate
Pi = inorganic phosphate

112
Q

In what three places does the synthesis of ATP occur?

A
  • Photophosphorylation - in chlorophyll-containing plant cells during photosynthesis
  • Oxidative phosphorylation - in the mitochondria of plant + animal cells during respiration
  • Substrate-level phosphorylation - in plant + animal cells when phosphate groups are transferred from donor molecules to ADP
113
Q

What is the energy released by ATP used for?

A
  • Metabolic processes e.g building of macromolecules
  • Movement - energy for muscle filaments to slide past each other, shortening the muscle fibre, contracting the muscle
  • Active transport - change shape of carrier proteins in plasma membranes so molecules can move against concentration gradient
  • Secretion - form lysosomes necessary for secretion of cell products
  • Activation of molecules - inorganic phosphate released during ATP hydrolysis can phosphorylate other compounds to make them more reactive + lower activation energy
114
Q

What is energy?

A

Something that allows work to be done. Can be changed between forms (e.g magnetic, light, heat) but never created or destroyed.
Most energy used by organisms is stored in chemical bonds in molecules.

115
Q

What are inorganic ions?
Where are they found?

A

An atom/group of atoms that have an electric charge by losing/gaining electrons. Not based on carbon
Found in cell cytoplasm + body fluids in high or low concentrations

116
Q

Name some common inorganic ions and their functions

A
  • Irons ions - found in haemoglobin to play a role in oxygen transport
  • Phosphate ions - structural role in DNA + storing energy in ATP
  • Hydrogen ions - determine pH of solutions + so function of enzymes
  • Sodium ions - important in transport of glucose + amino acids across plasma membranes
117
Q

Describe the structure of water

A

Two hydrogen atoms covalently bonded to an oxygen atom. O has a slight negative charge and H is slightly positive making it a dipolar molecule.
Positive pole of one molecule attracted to the negative pole of another, forming a hydrogen bond

118
Q

Give some properties of water that make it useful for life

A
  • High specific heat capacity
  • High latent heat of vaporisation
  • Cohesion
  • Adhesion
  • Surface tension
  • Good solvent
  • Metabolite
  • Not easily compressed
  • Transparent
119
Q

Explain the following properties of water and how they make it useful for life:
- High specific heat capacity
- High latent heat of vaporisation

A
  • Hydrogen bonds = high SHC because energy is used to break bonds before molecules can move faster. Doesn’t change temp easily = acts as a buffer against sudden temp changes. = Thermostable aquatic environments (habitats), minimises temp fluctuations inside cells (constant optimum conditions for enzymes for metabolism)
  • Hydrogen bonds = high LHV (takes a lot of energy to evaporate) = used as a cooling mechanism (body heat used to evaporate sweat)
120
Q

Explain the following properties of water and how they make it useful for life:
- Cohesion, Adhesion
- Surface tension
- Good solvent

A
  • Cohesion = water molecules stick together (form H bonds). Adhesion = water molecules stick to something else (H bonds). Together they allow water to be pulled up xylem vessels for one-way transport in plants
  • Surface tension = measure of how difficult it is to break surface of a liquid = allows some organisms to walk on water
  • Solvent - readily dissolves substances because dipolar molecules can surround ions (due to charge attraction) + prevent ionic bonds from forming, breaking up the substance
121
Q

Describe how the following properties of water make it useful for life:
- Metabolite
- Not easily compressed
- Transparent

A
  • Metabolite - used in hydrolysis, made by condensation, raw material in photosynthesis, chemical reactions take place in aqueous mediums
  • Not easily compressed = support (e.g turgor pressure in herbaceous plants, hydrostatic skeletons of animals)
  • Transparent = light can get to aquatic plants for photosynthesis, light-rays can penetrate jelly-like fluid that fills the eye + reach the retina

Biology (15 decks)

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