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AQA A Level Biology > Biological molecules > Flashcards

Biological molecules Flashcards

1
Q

What are phospholipids made up from?

A

1 phosphate containing group
2 fatty acids
1 glycerol

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2
Q

What are triglycerides made up from?

A

1 glycerol
3 fatty acids

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3
Q

Properties of triglycerides?

A

Used as energy storage molecules due to their long hydrocarbon tails of the fatty acids which contain lots of chemical energy
so lots of energy is released when they are broken down
INSOLUBLE IN WATER don’t affect water potential
so water wouldn’t enter the cells making them burst
HYDROPHOBIC fatty acid tails
Tails face inwards

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4
Q

Properties of phospholipids?

A

bilayer of cell membranes
control what enters and leaves the cell
Heads are hydrophilic
Tails are hydrophobic (don’t like water)
heads face outwards
centre of bilayer is hydrophobic
Water-soluble substances can’t pass through easily

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5
Q

Why do storage molecules needs to be insoluble?

A

Otherwise they would just dissolve and release whatever they were storing when they came into contact with water

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6
Q

Describe a condensation reaction

A

Joins two molecules together FORMING a chemical bonds e.g. ester, glycosidic, peptide and releases a molecule of water

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7
Q

Describe a hydrolysis reaction

A

Separates two molecules by breaking the chemical bond holding them together with the use of a water molecule

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8
Q

Reducing sugar test

A

Heat the sample with XS benedict’s reagent (contains copper II sulphate) and if positive then will form a bright red ppt (as copper I oxide is formed which is insoluble)

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9
Q

Non-reducing sugar test

A

Heat with an acid and then neutralise w/ sodium hydroxide
Then heat with XS benedict’s reagent and a red ppt forms for a positive result

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10
Q

Give an example of a non reducing sugar

A

sucrose

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11
Q

How is the tertiary structure formed?

A

Interactions between the different ‘R’ groups of the amino acids within in the polypeptide
Disulphide, ionic and hydrogen bonds causes further folding and thus forming the 3D specific tertiary structure

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12
Q

How do you reduce percentage uncertainty?

A

By increasing the volume measured or by using a larger sample size

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13
Q

How do you heat the samples during the test for reducing/non reducing sugars?

A

Heat samples using a boiling water bath

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14
Q

What bonds help to hold amylose in its helical structure?

A

Hydrogen

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15
Q

Why is starch a good storage molecule?

A

LARGE so cannot leave the cell
INSOLBULE doesn’t affect WP, no osmotic affect so doesn’t make cells swell

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16
Q

What is starch?

A

Plants store excess glucose as starch

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17
Q

What is starch made up of?

A

A mixture of two polysaccharides known as amylopectin and amylose

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18
Q

Structure of amylose

A

long unbranched alpha glucose
coiled helical structure due to angle of glycosidic bonds
compact - good for storage
fits more into small space

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19
Q

Structure of amylopectin

A

long branched alpha
side branches allow enzymes that break down the molecule to easily access the glycosidic bonds to release energy quickly

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20
Q

Structure of glycogen

A

animals store excess glucose as glycogen
polysaccharide of alpha glucose
HIGHLY branched as animals have a much HIGHER METABOLIC RATE
stored glucose can be released quickly
very compact so good for storage

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21
Q

Structure of cellulose

A

Beta glucose
structural support
long unbranched straight/linear chains of beta
form straight cellulose chains
these chains are linked together by hydrogen bonds to form strong fibres called MICROFIBRILS
these strong fibres allow cellulose to provide strong structural support for cell walls (plants)

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22
Q

Function of glycogen:

A

Acts as an energy store/reserve found in animals

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23
Q

Test for starch

A

Iodine dissolved in potassium iodide and gives a blue/black colour change for a positive result
Changes from browny-orange which indicates no starch

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24
Q

Uses of lipids

A

used as hormones e.g testosterone
resp substrates

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25
Q

What do you need to ensure not to do the emulsion test nearby and why?

A

NO open flames as ethanol is flammable

26
Q

What are disulphide bridges?

A

Covalent bonds between sulfur atoms
they are much stronger than the ionic and hydrogen bonds in proteins

27
Q

Describe the biuret test:

A

add a few drops of sodium hydroxide solution
then add some copper(II) sulfate solution
solution turns purple on positive result

28
Q

What is a catalyst?

A

offers alternative pathway with a lower activation energy
it is a substance that speeds up a reaction without being used up in the reaction itself

29
Q

In the induced fit model, what happens to the enzymes after the substrate is released?

A

The active site returns to its original shape and can bind to the next substate molecule

30
Q

What does catalase catalyse?

A

The breakdown of hydrogen peroxide

31
Q

When asked about a graph, what must you always do?

A

USE SPECIFIC VALUES FROM THAT GRAPH

32
Q

When talking about a competitive inhibitor, what must you ALWAYS include in the question?

A

The competitve inhibitor and the substrate have a SIMILAR SHAPE

33
Q

What is formed when there is a condensation reaction between two nucleotides?

A

a phosphodiester bond

34
Q

The two polynucleotide strands in DNA are what?

A

ANTIPARALLEL

35
Q

How do two polynucleotide strands join together?

A

Hydrogen bonds between complementary base pairs, e.g. A and T, C and G

36
Q

How can you tell which direction a DNA strand is running in?

A

One end of a polynucleotide has a hydroxyl group and the other end has a phosphate group

37
Q

Difference between RNA and DNA?

A

RNA: uracil, single stranded, ribose, shorter (relatively short)
DNA: thymine, double stranded, deoxyribose, longer

38
Q

What does DNA polymerase do?

A

Condensation reaction that joins adjacent nucleotides together Catalyses the formation of the phosphodiester bonds between nucleotides (not between the new and old strand, they join together via hydrogen bonds during DNA replication)

39
Q

Scientists names who discovered the structure of DNA

A

(James) Watson and (Francis) Crick

40
Q

What is the active site of DNA polymerase only complementary to during DNA replication?

A

The three prime end of the newly forming DNA strand

41
Q

How is the new strand formed, in what direction?

A

5’ to 3’ direction as DNA polymerase can only be bonded to the 3’ end
It moves along the template strand in the 3’ to 5’ direction

42
Q

The two strands in DNA are antiparallel, what does this mean for DNA polymerase?

A

That the second DNA polymerase that is working on the second template strand is moving in the opposite direction

43
Q

What two scientists validated the semi-conservative replication theory using an experiment, what was their experiment?

A

Meselson & Stahl
using two isotopes of nitrogen (heavy + light) DNA settled in centrifuge between light and heavy
Heavy nitrogen placed in light nitrogen containing nutrient broth
Contained mixture of heavy and light thus semi-conservative

44
Q

How does ATP move to the part of the cell that needs it?

A

diffuses

45
Q

where is the energy stored in ATP?

A

In high energy bonds between the phosphate groups - released by a hydrolysis reaction

46
Q

ATP isn’t energy, it’s a what?

A

A STORE OF ENERGY

47
Q

What four things is water useful for? Why?

A

Metabolite - condensation + hydrolysis
Solvent - most metabolic reactions take place in solution e.g. cytoplasm
Helps with temperature control due to its high latent heat and high specific heat capacity
Cohesive water molecules, helps water transport in plants + other organisms

48
Q

What is a metabolic reaction and what is a metabolite?

A

A chemical reaction that happens in a living organism in order to keep it alive, a metabolite is a substance that is involved in a metabolic reaction

49
Q

Why do polar molecules dissolve in water and give an example of polar molecule that dissolves in water?

A

Glucose, and they dissolve in water as hydrogen bonds form between them and the water molecules

50
Q

How does salt dissolve in water?

A

Na+ and Cl- so negative oxygen is attracted to the positive Na and the positive H is attracted to the negative Cl –> ions become totally surrounded by water molecules

51
Q

What is latent heat?

A

The heat energy that is needed to change a substance from one state to another

52
Q

Why is it important that water has a high specific heat capacity?

A

Enzyme activity is affected by temperature - important biological processes need enzymes to work, they may not if the organism’s temperature is not stable

53
Q

Why is having a high latent heat of vapourisation good?

A

Lots of energy is needed to break the hydrogen bonds holding water molecules together in order for water to become a gas, therefore lots of energy is used up when water evaporates, organisms use water loss through vapourisation in order to cool down, when water evaporates it carries heat energy away from the surface –> helps lower the temperature

54
Q

How does water have a high specific heat capacity?

A

SHC is the heat energy needed to raise the temperature of 1 gram of a substance by 1 degrees celcius, when water is heated, a lot of energy is needed in order to do this as lots of energy is needed to break the hydrogen bonds between the water molecules
meaning that water doesn’t experience rapid temp changes
good habitat underwater as it is more stable than land
maintains a constant internal body temperature also

55
Q

Why is it good that water is cohesive?

A

Attraction between molecules of water, stick together because they are polar, maintains a column of water than can flow, good for transporting substances, strong cohesion also results in a high surface tension when it comes into contact with air, this is why sweat forms droplets and some insects can ‘walk on water’ e.g. pond skaters

56
Q

Explain five properties that make water important for organisms? EQ

A

Cohesion BETWEEN WATER MOLECULES provides surface tension, supporting small organsims
A metabolite in condensation/hydrolysis and photo/resp
High latent heat of vapourisation provides a cooling effect for organisms as heat energy is lost through water leaving the body as a gas
High specific heat capacity as it can buffer its change in temperature
Polar molecule so can support columns of water
Good solvent for many metabolic reactions thus allowing transport of substances

57
Q

Role of iron ions?

A

each (4) polypeptide chain contains an iron ion (Fe2+) in the centre
Fe2+ binds to the oxygen in haemoglobin. When oxygen binds, it is oxidised to Fe3+ until the oxygen is released
Help transport oxygen around the body

58
Q

Role of phosphate ions?

A

affects osmosis/ water potential
as it is part of the hydrophilic/water soluble part of the phospholipid bilayer
joins nucleotides together through the formation of phosphodiester bonds
used to produce ATP
makes other molecules more reactive by phosphorylating them
as it binds to other moleculesand causing them to change shape
When a phosphate us bonded to another molecule it is known as a phosphate group e.g. ATP DNA RNA
the bonds between the phosphate groups store energy in ATP, in DNA RNA the phosphate groups allow nucleotides to join together to form polynucleotides

59
Q

Role of sodium ions?

A

glucose and amino acids need help crossing cell membranes
They can be transported across the membrane alongside sodium ions
co-transport
sodium ions actively transported OUT of cells against conc grad
CREATES sodium CONC GRAD
so they can diffuse down conc grad with glucose/AA into cells
affects osmosis/WP

60
Q

Role of hydrogen ions?

A

pH calculated on conc of H ions
more H+ the more acidic - lower pH
enzyme-controlled reactions are all affected by pH

61
Q

What does an ion’s role determine?

A

Whether it is present in high or low concentrations

AQA A Level Biology (23 decks)

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