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AQA A Level Biology > Biological Molecules > Flashcards

Biological Molecules Flashcards

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1
Q

What are the long chains of monomer sub units called?

What process is this called?

A

Polymers

Polymerisation

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2
Q

What is the reaction called when each time a new sub-unit is attached, a molecule of water is formed?

A

Condensation reaction

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3
Q

What is it called when water molecules are used to break the bonds that link the sub-units of a polymer?

A

Hydrolysis reaction

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4
Q

What is a molar solution?

A

A solution that contains one mole of solute in each litre of solution.

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5
Q

What are some examples of monomers?

A

Monosaccharides, amino acids and nucleotides

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6
Q

Pattern of sugars joining (saccharides)

A

A single monomer is a monosaccharide -
two monosaccharides = disaccharide
many monosaccharides = polysaccharide

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7
Q

What are examples of monosaccharides?

isomers?

A

glucose, galactose, fructose

glucose has alpha and beta glucose isomers

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8
Q

Test for reducing sugars

A

Add 2cm^3 of food sample to test tube. grind if not in liquid form.
Add equal volume of Benedicts reagent.
Heat in gently boiling water for five minutes.
If it turns orange brown, then reducing sugar present

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9
Q

Disaccharides made from monosaccharides joining

What are these reactions called and what are the bonds called?

A

glucose + glucose = maltose
glucose + fructose = sucrose
glucose + galactose = lactose
Condensation reaction and glycosidic bond

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10
Q

Test for non reducing sugars

A

start with sample in liquid form
do reducing sugar test first and if no colour change, then non reducing sugar may be present.
Boil the food sample with dilute hydrochloric acid, HCl hydrolyses any disaccharide present into monosaccharides.
Neutralise with some sodium hydrogencarbonate solution.
Test with pH paper to check that the solution is akaline
Heat with 2 cm^3 Benedicts in gently boiling water for 5 mins.
Will turn orange brown, shows non reducing sugar was present, not reducing sugar

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11
Q

What are advantages of polysaccharides?

Examples of polysaccharides?

A

Very large molecules so insoluble - suitable for storage
When hydrolysed, broken down into disaccharides and monosaccharides.
Cellulose
Starch

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12
Q

Test for starch

A

2cm^3 of sample into test tube
Two drops of iodine solution and shake
Colour change to blue-black

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13
Q

Advantages and roles of starch

Where is it found?

A

insoluble - doesn’t affect water potential, water is not drawn into cells by osmosis
large and insoluble - does not diffuse out of cells
compact - a lot can be stored in a small space
when hydrolysed, forms alpha glucose, easily transported and readily used in respiration
branched form has many ends, glucose monomers can be released very rapidly.
in plant cells, never in animal cells

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14
Q

Advantages and roles of glycogen

Where is it found?

A

insoluble - does not tend to draw in water into cells by osmosis
insoluble - does not diffuse out of cells
compact - lot can be stored in small space
more highly branched than starch - rapdily broken down to glucose monomers and this is useful as animals have higher metabolic rate + respiratory rate
Found in animals and bateria but never in plant cells

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15
Q

Features of cellulose

What is the main role of cellulose?

A

made of beta glucose - form straight, unbranched chains
cellulose molecular chains run parallel to each other and are cross linked by hydrogen bonds which add collective strength
molecules grouped to form microfibrils - in turn grouped to form fibres - provides more strength.
provides rigidity in plant cell walls, to prevent it from bursting as water enters through osmosis

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16
Q

What are lipids soluble and insoluble in?

A

Soluble in organic solvents (such as alcohols and acetone)

Insoluble in water

17
Q

What are the two main groups of lipids?

A

Phospholipids and triglycerides

18
Q

What are four roles of phospholipids?

A

Source of energy- when oxidised, provide more than twice the energy as the same mass of carbohydrates
Waterproofing- insoluble in water
Insulation- fats are slow conductors of heat + electrical insulators in myelin sheath
Protection- fat usually stored around delicate organs

19
Q

What are triglycerides and how are they formed?

A

Three fatty acids combined with glycerol.
Fatty acids form an ester bond with glycerol in a condensation reaction
Hydrolysis of triglyceride produces glycerol and three fatty acids

20
Q

Explain what it means for triglycerides to be saturated, mono-unsaturated and polyunsaturated

A

Saturated- no carbon-carbon double bonds
Mono-unsaturated- single double bond
Polyunsaturated- more than one double bond present

21
Q

4 ways the structure of triglycerides are related to their properties

A
  • high ratio of energy-storing- carbon-hydrogen bonds to carbon atoms so excellent source of energy
  • low mass to energy ratio - good storage molecule
  • large, non-polar molecules - insoluble in water, and so does not affect osmosis in cells or their water potential
  • high ratio of hydrogen to oxygen atoms - release water when oxidised, important water source for organisms in dry environment
22
Q

What is the structure of a phospholipid and what do these features do? (two parts)
Is a phospholipid polar or non polar?

A

similar to triglyceride- one fatty acid replaced with by a phosphate molecule
phosphate makes up hydrophilic head
fatty acids make up hydrophobic tail
Polar

23
Q

How does the structure of a phosphlipid relate to its function?

A

Polar, along with hydrophilic phosphate + hydrophobic fatty acid forms a bilayer within cell surface membrane (in an aqueous environment)
Can form glycolipids, which are important in cell recognition

24
Q

Test for lipids

WHAT IS THE KEY WORD TO USE IN EXAM QUESTION ANSWERS?

A

Take completely empty, grease-free tube
Add 5cm^3 of ethanol to 2cm^3 sample
Shake tube thoroughly to dissolve any lipid present
Add 5cm^3 water and shake gently
A cloudy-white colour indicates lipid present
AN EMULSION IS MADE
As a control, repeat with water instead of sample

25
Q

If amino acids= monomer then what is the polymer?

A

Polypeptide

26
Q

What are the four different components of an amino acid?

A

Amino group
Carboxyl group
hydrogen atom
R (side) group

27
Q

What is it called when two amino acid monomers join?
What is this reaction called?
What is the name of the bond formed?
What is this bond between?

A

Dipeptide is formed
Condensation reaction
Peptide bond between carbon atom of one and nitrogen group of another

28
Q

What is a primary protein?

What does it determine?

A

It is a sequence of amino acids in a polypeptide chain.
It determines the ultimate shape and hence the protein’s function. If there is a change in just a single amino acid in the primary structure, then it can lead to a change in the protein.

29
Q

What is the secondary structure of proteins?

A

When amino acids readily form weak hydrogen bonds, and are twisted into a 3D shape of an alpha helix

30
Q

What is the tertiary structure of proteins?
What are the three different bonds?
Why is the 3D structure important?

A

When alpha helix of secondary protein structure is twisted and folded to become more complex and specific.
Disulfide bonds- fairly strong, not easily broken
Ionic bonds- weaker than disulfide bonds, easily broken by changes in pH
Hydrogen bonds- numerous but easily broken
Makes each protein distinct and is key for function

31
Q

What is the quaternary structure of a protein?

A

A number of individual polypeptide chains linked in various ways.
Can also have a prosthetic group attached.

32
Q

Test for proteins

A

Sample in test tube
Add equal volume of NaOH at rtp
Add a few drops of Biuret reagent (very dilute copper(II) sulfate)
Mix gently
If protein present, blue to violet (purple)

33
Q

What are enzymes?

A

Globular proteins that act as catalysts.

They lower the activation energy level and provide an alternative pathway

34
Q

How do enzymes work in terms of structure?

A

Enzymes have an active site.
The molecule that the enzyme acts on is called the substrate.
This fits neatly into this depression- called the enzyme-substrate complex.

35
Q

What is the induced fit model of enzyme activity?

A

The active site forms as the enzyme and substrate interact.
Enzyme is flexible and can mould itself around the substrate.
The very act of colliding with its substrate is a change to the enzyme’s environment and so it’s changes shape.

36
Q

What are four factors that affect enzyme action?

Explain what they do and how:

A

Temperature - rise increases kinetic energy, RoR increases, temp rise also breaks bonds and enzyme changes shape - denaturation
pH - each enzyme has an optimum pH, if it goes above then likely to be denatured, a change in pH alters the charges on amino acids that make up the active site of the enzyme
Enzyme concentration - if substrate is limiting, then increase in enzyme conc. will have no effect on RoR
Substrate concentration - RoR increases in proportion with conc. of substrate. as more substrate is added, the active sites gradually get filled, until the point that all of them are working as fast as they can.

37
Q

What are competitive inhibitors?

A

Have a molecular shape similar to that of the substrate.
They are then able to occupy the active site of an enzyme.
Blocks the substrate from joining.
If the substrate conc. is increased, the effect of the inhibitor is reduced.

38
Q

What is a non-competitive inhibitor?

A

They attach themselves to the enzyme at a binding site which is not the active site.
Alters the shape of the enzyme and the active site, and a substrate molecule can no longer occupy it.
An increase in substrate conc. does not decrease the effect of the inhibitor.

AQA A Level Biology (9 decks)

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