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OCR Biology > ✨Module 2: Biological molecules > Flashcards

✨Module 2: Biological molecules Flashcards

1
Q

Carbohydrates contain …
Lipids contain …
Proteins contain …
Nucleic acids contain …

A

CHO (formula of CH2O)
CHO but with low % of O
CHON(P)S
CHONP

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2
Q

Explain the structure of water.

A

Covalently bonds. Unequal share of electrons so they move toward oxygen as it has a larger proton number/bigger atoms. Hydrogen are f+, oxygen are f-. Water is POLAR (unequal share of electrons) due to different charges over its surface. In polar bonds, electrons are shared, not lost. Hydrogen bonds are formed as the f- oxygen attracts the f+ hydrogen atom from a different water molecule. These bonds are weak compared to ionic or covalent. These give water lots of good properties.

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3
Q

What is water ionisation?

A

H+ and OH- ions formed is important for metabolic processes such as pH regulation.

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4
Q

Why does water have a high b.m.p?

A

Lots of hydrogen bonds require lots of energy to break.

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5
Q

Why does water make a good transport medium?

A

Liquid at room temp so doesn’t change state easily, providing a constant environment. Also due to adhesion and cohesion - water can rise up a narrow tube against the force of gravity (capillary action).

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6
Q

Define cohesion. Why does water have high cohesion?

A

Attraction between same substances (2 waters). They stick due to polarity/hydrogen bonding.
This property helps water to flow, water transported in xylem of plants.

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7
Q

Define adhesion. Why does water have high adhesion?

A

Attraction between different substances. Stick to others due to hydrogen bonding. Nutrients can be transported against gravity in plants ie capillarity.

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8
Q

Define latent heat. Why does water have high latent heat of evaporation?

A

Heat energy needed to change a substance from one state to the other, without changing temperature.
Because it takes a lot of energy to break the strong hydrogen bonds between water molecules, so lots of heat energy is used when water evaporates. It allows animals to cool themselves by sweating.

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9
Q

Why does water have high surface tension?

A

Due to highly cohesive forces, which require large amount of energy to break. Helps blood to flow through narrow vessels. Allows water to form a meniscus - insects can walk on water without sinking.

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10
Q

Define specific heat capacity and explain why water has a high specific heat capacity.

A

Energy needed to raise the temp of 1g of substance by 1 degrees C. Hydrogen bonds require a large amount of energy to break, so maintains homeostasis and a stable habitat.

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11
Q

Why is transparency important for water?

A

Light can pass through for photosynthesis and visibility in aquatic environments.

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12
Q

Explain why ice floats. Why is this important?

A

Water molecules are held further apart in solid form. Each H2O molecule forms 4 hydrogen bonds, making a lattice shape. Ice forms an insulating layer on top of water, so water below doesn’t freeze.

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13
Q

Water is a universal solvent. Why is that and how does it benefit?

A

Many solutes (amino acids) are also polar so the + and - attract ions in water. Important ions can dissolve in water in blood and be transported in the body.

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14
Q

Polar molecules are …

A

Hydrophilic as they dissolve easily in water.

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15
Q

Why is water difficult to compress?

A

Strong intermolecular forces between molecules. Provides support and turgidity in plant cells.

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16
Q

What is an inorganic ion?

A

Charged particles that aren’t part of the larger molecule and has no carbon (few exceptions). Typically derived from non-living sources.

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17
Q

Organic ions contain …

A

At least 1 hydrogen-carbon bond. Typically derived from living organisms.

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18
Q

Ca2+ function.
Na+ function.
K+ function.

A

Transmitting nerve impulses, bone formation.
Lack of calcium/vit D leads to rickets.

Na+ helps nerve impulse transmission, muscle contraction. Lack of sodium leads to hyponatremia.

K+ is same as sodium. Also responsible for opening and closing stomata in leaves. Hypokalaemia.

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19
Q

H+ function.
NH4+ (ammonium) function.

A

pH determination, ATP synthesis in mitochondria in cellular respiration.

Absorbed from soil by plants and uses nitrogen from it to create nucleic acids and amino acids/to make chlorophyll. If plant doesn’t have enough, leaves turn yellow. NH4+ binds to CO2 to make urea.

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20
Q

NO3- (nitrate) function.
HCO3- (hydrogen carbonate) function.
Cl- function.

A

Absorbed from soil and used in same way as ammonium. Makes DNA.

Acts as a buffer aka bicarbonate ion.

Co-factor for enzyme amylase, transmitting certain nervous impulses.

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21
Q

PO43- (phosphate)
OH-

A

Key component in phospholipid bilayer. Important to make nucleotides and ATP.

Affects pH of substances. OH- are bases.

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22
Q

Why is maintaining pH important?

A

Too high or low will cause proteins to denature.

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23
Q

What are macromolecules with examples?

A

Have a large number of atoms e.g. proteins, carbohydrates.

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24
Q

Monomers are …
Polymers are …

A

Small simple molecules e.g. amino acids.
Large complex molecules made when monomers join together. They are a group of macromolecules.

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25
Q

Are lipids polymers?

A

No, they don’t consist of repeating units.

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26
Q

Monomers to polymers?
Polymers to monomers?

A

Condensation - glycosidic bond forms between the monomers and for each formation, a molecule of water is released.

Hydrolysis - molecule of water reacts with the glycosidic bond and breaks it.

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27
Q

What are carbohydrates?

A

Polymers made up of carbon, hydrogen, oxygen in the ratio CH2O. Long chains of sugar units called saccharides.

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28
Q

Facts about glucose molecules?

A

Glucose is the main energy source in plants. It’s soluble due to the hydrogen bonds formed between hydroxyl group (OH-) and water. This makes it easily transported.
Its chemical bonds contain a lot of energy.

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29
Q

What is a hexose monosaccharide?

A

Contain 6 carbons in their compound.
Glucose, fructose, galactose are isomers as they all have the formula C6H12O6.

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30
Q

What is a pentose monosaccharide?

A

Has 5 carbons in their compound. They function as genetic information. Ribose, deoxyribose.

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31
Q

What is a triose monosaccharide?

A

Has 3 carbons, found in respiration.

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32
Q

Disaccharide? What are they involved in?

A

2 monosaccharides joined together as a glycosidic bond in a condensation reaction. Maltose, lactose, sucrose.
Involved in transport in plants, energy source.

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33
Q

What are polysaccharides?

A

Formed when many monosaccharides join together like glycogen, cellulose, starch.

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34
Q

Explain what starch is.

A

Polysaccharide made from alpha glucose which is the main energy storage in plants. Cells get energy from glucose so when plant needs more glucose it breaks down starch.

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35
Q

What are the 2 types of starch polysaccharide?

A

Amylose and amylopectin.

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36
Q

Explain the structure of amylose.

A

Long, unbranched chain of alpha glucose joined by 1,4-glycosidic bonds. Angles of the glycosidic bonds and hydrogen bonds give it its helix structure.
Makes it compact and good for storage as you can fit more in small space.

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37
Q

Explain the structure of amylopectin.

A

Long, branched chain of alpha glucose with 1,4 and 1,6-glycosidic bonds.
More sites for enzyme action so glucose is broken down more quickly and raises blood glucose more readily than amylose.

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38
Q

Explain what the polysaccharide glycogen is and its structure.

A

Made from alpha glucose which is the main energy storage in animals. Excess glucose is stored as glycogen. Similar structure to amylopectin but has more side branches.
Makes it compact and good for storage. Branches mean glucose molecules can be added or removed quickly.
Both amylopectin and glycogen are insoluble so no osmotic effect (unlike glucose).

39
Q

What if glycogen was soluble?

A

It could lead to thicker cell wall in plants as water would move into the cell, or animal cells would burst.

40
Q

To release glucose needed for respiration …

A

Starch/glycogen undergo hydrolysis, requiring the addition of water molecules.

41
Q

Explain what cellulose polysaccharide is and its structure.

A

Long, straight (due to rotation of glucose), unbranched chain of beta glucose where alternate molecules are inverted. It has 1,4-glycosidic bonds but not 1,6.
It’s unable to coil or form branches.
Hydrogen bonds between separate chains form microfibrils, providing structural support for plant cell walls.
Cellulose is insoluble in water so no osmotic effect.

42
Q

Most flowering plants don’t have centrioles. So what do they rely on for cell division?

A

They have centrosomes that are outside the nucleus. They move to the poles of the cell and facilitate the formation of spindle fibres in cell division.

43
Q

Lipids (macromolecules) are in what 2 forms?

A

Fats (solid at room temp) and oils (liquid at room temp).

44
Q

Give some facts about lipids.

A

Insoluble in water but soluble in organic solvents like alcohol. Lipids are non-polar as the C-C and C-H bonds are non-polar. So lipids are hydrophobic and repel water as water is polar.
Also, oil and water don’t mix.

45
Q

What are the 3 types of lipid?

A

Triglycerides, phospholipids, cholesterol.

46
Q

Explain what a triglyceride is and its structure.

A

1 molecule of glycerol (member of alcohol group) with 3 fatty acids. The fatty acids have a COOH group at one end and a CH3 group at the other end.
Entire molecule is hydrophobic and insoluble in water due to fatty acid tails being non-polar.

47
Q

What happens when glycerol and fatty acids react together?

A

3 ester bonds form between each fatty acid. The OH group on glycerol and fatty acid react. Each ester bond is formed by a condensation reaction to release a molecule of water. ESTERIFICATION.

48
Q

Triglycerides break down to …

A

3 fatty acids and glycerol via hydrolysis by breaking the ester bonds by adding 3 molecules of water.

49
Q

The number of ‘C’s determine the …

A

Fatty acid name.

50
Q

What is a saturated fatty acid?

A

Doesn’t have double bonds between carbon atoms in their hydrocarbon tails. This makes the structure rigid as all carbon atoms form the max number of bonds with hydrogen. SOLID at room temp.

51
Q

What is an unsaturated fatty acid?

A

Have at least 1 C=C bond, causing the chain to kink and be flexible, so can’t pack closely together. LIQUID at room temp.

52
Q

The greater the number of unsaturated bonds …

A

Weaker the intermolecular forces so lower b.m.p.

53
Q

Longer the chain of fatty acid …

A

More likely it is a solid.

54
Q

What are the actual functions of triglycerides?

A

They are good storage molecules as the long fatty acid tails contain lots of energy.
Triglycerides are also insoluble so no osmotic effect. They form micelles when exposed to water.
Also thermal insulation in penguins to reduce heat loss.

55
Q

Why do storage molecules need to be insoluble?

A

So they don’t dissolve and release their contents.

56
Q

What is a phospholipid?

A

One of the fatty acids in the triglyceride is replaced by a phosphate group.
Phosphate heads are hydrophilic as it is negatively charged and is soluble in water.
Phospholipids also form micelles in aqueous solution as the tails are non-polar. The overall molecule is POLAR.

57
Q

What is the general function of phospholipids?

A

Make up the phospholipid bilayer which controls what goes in and out of the cell.

58
Q

What is the function of cholesterol?

A

They have a hydroxyl group at one end which is hydrophilic, and the rest of the molecule is hydrophobic.
Cholesterol keeps the membrane less fluid and more rigid: cholesterol can fit in the membrane and bind to the hydrophobic tails, making them pack more closely together.
Cholesterol also produces Vit D, which takes place in the skin in response to UV light.

59
Q

Triglycerides are …
Phospholipids are …
Cholesterol is …

A

Non-polar
Polar (due to phosphate heads being hydrophilic)
Non-polar (although it has a small OH group) so doesn’t mix with water.

60
Q

Qualitative testing?
Quantitative testing?

A

Whether a substance is present in a sample or not.
Tells us the conc of substance in a sample.

61
Q

How to prepare a solution of a solid?

A

Crush the solid with distilled water and filter out the solid.

62
Q

What is a reducing sugar?

A

It reduces another molecule. Reducing sugars contain an aldehyde group or a COH group.
All monosaccharides and disaccharides (lactose and maltose) are reducing sugars.

63
Q

What is Benedict’s reagent and why is it used to test for reducing sugars?

A

An alkaline solution of blue copper sulphate. Reducing sugars reduce the Cu2+ (blue) in Benedict’s reagent to Cu+ (red).

64
Q

Test for reducing sugars.

A

Place sample in boiling tube, add Benedict’s reagent, place it in a water bath for 5 mins.

65
Q

What is the positive result for a reducing sugar?
What does it mean if the solution remains blue?

A

Brick-red precipitate. The greater the conc of reducing sugar, the greater the colour change and more precipitate is formed.

It could mean there are non-reducing sugars in the sample or no sugars at all.

66
Q

What is a non-reducing sugar?
Give an example.

A

It can’t reduce something as it lacks aldehyde and ketone groups. They don’t react with Benedict’s so remains blue after warming.
Sucrose.

67
Q

Describe the test procedure for non-reducing sugars.

A
  1. Boil a new solution containing sugar in a water bath with dilute HCL. The acid will break down the non-reducing sugar /glycosidic bonds into monosaccharides.
  2. After adding acid, neutralise the solution with sodium hydrogen carbonate.
  3. Use red litmus to see when neutralised.
  4. Then we do Benedict’s test as normal.
68
Q

Describe the test for starch.

A
  1. Add a few drops of iodine in potassium iodide solution to the sample.
    The iodine is in potassium iodide solution as iodine is insoluble in water.

If starch is present, iodide ions in the solution interact with the centre of starch molecules, producing a complex with a distinctive blue-black colour.

69
Q

Test for lipids/emulsion test.

A

Add ethanol then water and shake (to ensure ethanol has dissolved).

If lipids are present, a milky white emulsion forms at the top, due to lipids being insoluble in water.

70
Q

Caution with ethanol?

A

Ethanol is flammable to make sure to use it away from open flames.

71
Q

Test for proteins/biuret test.

A

Add a few drops of NaOH to make the solution alkaline, add a few drops of CuSO4 until the sample turns blue. Leave for 5 minutes.

The solution will turn purple in the presence of a peptide bond. NaOH and CuSO4 reacts with the peptide bond.

72
Q

Give 2 quantitative measures.

A

Colorimetry and biosensors.

73
Q

Explain how biosensors work.

A

It measures the conc of substances in solution. The interaction between a biological agent (like enzymes, antibodies) and the test substance produces a chemical signal. The transducer receives this and can be turned into an electrical signal. This is then analysed to quantify the conc.

74
Q

Describe the structure of an amino acid.

A

They have a carboxyl group and amine group attached to the carbon.
The difference is the variable R group. Amino acids are linked by peptide bonds, and a molecule of water is released (condensation). Hydrolysis adds a molecule of water to break the peptide bond.

75
Q

What is peptide bond?

A

A very strong covalent bond.

76
Q

What is the primary structure of a protein?

A

Linear sequence of amino acids held by peptide bonds (only in primary). Primary structure determines function and chemical properties. This is because differences in amino acids will influence how the polypeptide folds to give its final shape.

77
Q

Secondary structure of protein.

A

-NH (f+) and -CO (f-) in adjacent amino acids form hydrogen bonds, causing folding and coiling into alpha helixes and beta pleated sheet.

Alpha helixes are spirals that form due to coiling.
Beta has 2 amino acid chains running side by side that form due to folding.

The hydrogen bonds that form between amino acids help stabilize the protein structure and prevent it falling apart.
The primary structure can be folded/coiled further into the tertiary structure.

78
Q

What is the tertiary structure and what interactions between the R groups is it composed of?

A

3D arrangement of entire polypeptide. Made up of combinations of alpha helixes and beta pleated sheets.
Ionic bonds, disulphide bridges, hydrophobic forces, weak hydrogen bonds.

tertiary structure is critical to the function of proteins as it determines their overall shape and activity.

79
Q

Explain the function of each type of bond in a tertiary structure of protein.

A

Ionic bonds - electrostatic attractions between oppositely charged R groups on different amino acids. Between carboxyl group and amine groups not involved in peptide bond.

Disulphide bridges - form between 2 molecules of cysteine. The sulphur atom on one cysteine can covalently bond with the sulphur atom of another cysteine.

Hydrophobic forces between non-polar amino acids with the interior of the protein. They are pushed inside due to water repelling and hydrophilic R groups are more likely to be on the outside.

Hydrogen bonding - form between f+ and f- R groups in the polypeptide chain.

80
Q

Strength of the bonds in the tertiary structure.

A

Disulphide bridge>ionic bonds>hydrogen bonds

81
Q

What is the quaternary protein structure in proteins?

A

Multiple different polypeptide chains coming together and undergoing additional folding to form the final protein structure. It features all bonds from the tertiary structure and covalent bonds between the chains.

82
Q

Dimers are …
Trimers are …

A

Proteins made up of 2 polypeptide chains.
Proteins made up of 3 polypeptide chains.

83
Q

Globular proteins involve …
Fibrous protein involve …

A

Primary, secondary, tertiary, quaternary.
Primary, secondary, quaternary.

84
Q

Describe the structure of globular proteins.

A

Spherical shape as the hydrophobic R groups fold inwards whilst the hydrophilic R groups are externally exposed.
Globular proteins are water-soluble due to hydrophilic R groups.

85
Q

Functions of globular proteins?

A

All enzymes are globular proteins as their round shape can be altered appropriately to fit their target sites with high specificity. Amylase, pepsin.
Due to their soluble nature, globular proteins function well as transport proteins as they can cross cell membranes. An example is haemoglobin, which transports oxygen.
Their solubility also makes globular proteins suitable as hormones. An example would be insulin, which regulates blood sugar levels.

86
Q

GLOBULAR PROTEIN: Haemoglobin.

A

Quaternary protein made up of 4 polypeptide units: 2 alpha and 2 beta, which are each covalently bonded to a haem prosthetic group. This protects it from being destroyed by the oxygen. Haem contains iron, which oxygen binds to.

Haemoglobin is a conjugated protein as it’s globular and has a non-protein part called a prosthetic group.

Because the hydrophilic side chains are on the outside and hydrophobic inside, haemoglobin is soluble in water and good for transporting oxygen in the blood.

87
Q

GLOBULAR PROTEIN: Insulin.

A

Quaternary protein with 2 polypeptide chains held together by disulphide bonds. Water soluble so are good messengers and can be transported in the blood to tissues. Hormones also need to have a precise shape as they have to fit into specific receptors in plasma membrane to have their effect.

88
Q

GLOBULAR PROTEIN: Catalase.

A

Quaternary protein containing 4 haem prosthetic groups. The Fe2+ in the haem group allows the catalase to break down H2O2 faster.

89
Q

Describe the structure of fibrous proteins.

A

They are long chains of repeated amino acid sequences that form long polypeptide chains. These chains twist together to form fibrous proteins. They don’t fold into complex 3D shapes like globular.

90
Q

Function of fibrous proteins?

A

As fibrous proteins are stable and insoluble structures, they act well as structural proteins which support and protect tissues.

Fibrous proteins are water insoluble. As the hydrophobic parts of the polypeptide chains are not folded away from the external environment, fibrous proteins are not soluble in water.

91
Q

FIBROUS PROTEIN: Keratin.

A

Provide structure to hair and nails. Lots of strong disulphide bridges to form strong insoluble materials. Hair contains fewer of these bonds so it is more flexible than nails, which has more DS bonds.

92
Q

FIBROUS PROTEIN: Collagen.

A

Type of connective tissue in the body. The proteins in collagen are joined together by hydrogen and covalent bonding, both of which are extremely strong and stable bonds.
Collagen fibres provide support and tensile strength to many structures, such as in skin, muscles, and bones.

93
Q

FIBROUS PROTEIN: Elastin.

A

Found in elastic fibres such as in the alveoli in lungs, which give flexibility when needed to expand and return to its normal size.

OCR Biology (19 decks)

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