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A level biology-CIE > Biological Molecules > Flashcards

Biological Molecules Flashcards

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1
Q

What is macromolecule?

A

A macromolecule is a large biological molecule such as a protein, polysaccharide or a nucleic acid.

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2
Q

Define monomer

A

Elememnts make up monomers.
Simplest repeating unit of a polymer.
For example:
Monosachharides (carbohydrate monomers).
Amino Acids-protein
Nucleotides-DNA and RNA and ATP

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3
Q

Define polymers

A

Polymers are made of repeating monomers joined end to end in a process called polymerisation.
For example:
Polysaccharides-carbohydrates
Polypeptides-protein
Polynucleotides-nucleic acid

Polymers become so large in size and become a macromolecule which is a giant molecule.

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4
Q

Explain polymerisation

A

Condensation: Two molecules combine
removal of water
Hydrolysis: Molecule breaks down and addition of water.

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5
Q

Describe carbohydrates

A

Made of C H and O
General formula: (CH2O)n.
3 groups:
1. Monosaccharides
2. Disachharides
3. Polysaccharide

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6
Q

What is the role of carbohydrates in living organism?

A
  1. Source of energy in respiration
    E.G Starch and glycogen
    High C-H bonds→Energy→ATP
  2. Building blocks for larger molecules
    e.g. RNA,DNA,ATP,Glycoproteins and glycolipids in plasma membranes.
  3. Structural support
    e.g. cellulose
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7
Q

Describe monosaccharides

A

Single sugar molecule
Soluble, sweet
Molecular formula: CnH2nOn
Classified according to number of carbon atoms.
3C-triose(C3H6O3)
5C-pentose(C5H10O5)
6C-hexose(C6H12O6)

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8
Q

Describe linear structures vs ring structures carbohydrates.

A

In pentose and hexose sugars (5C and 6C).
Chain of carbon atoms are long enough to close up on itself.
🡢Ring structure
🡢More stable, more common

5 carbon is outside of the ring.

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9
Q

Describe the ring structure of glucose

A

Same molecular formula (C6H12O6), same chemical substance, different form.
Close up at C1 and C5
Has 2 isomers: alpha gucose and B glucose.
In alpha glucose carbon 1 has OH towards bottom.

We start counting clockwise from the oxygen atom.

DDUD-alpha males
UDUD-BETA
Baloon in air-beta

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10
Q

describe the reaction in which monosacharides converted to disacharides.

A

Disaccharides are soluble and sweet.
Formed from two monosacharides
Through a process called condensation.
1 hydroxyl group (-OH) + Hydrogen atom (H).
Produce 1 water molecule (H2O).
Glycosidic bond is formed (covalent bond)
reaction controlled by oxygen.
Glycosidic bond called 1,4 aplha glucose.

sometimes glycosidic bond referred to as oxygen bridge.

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11
Q

Describe the breakdown of disaccharides to monosaccharides.

A

break down of disaccharides to monosacharides.
Hydrloysis
Requires addition of water
reaction controlled by enzymes.

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12
Q

What are the types of polysaccharides?

A

Starch
Glycogen
cellulose

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13
Q

How are polysacharides made?

A

Polymers/macromolecules
Made via condensation
Glycosidic bonds

Not sugars🡢not sweet, insoluble
e.g. starch glycogen and cellulose.

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14
Q
A
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15
Q

Describe the polysaccharide starch

A

Storage molecule in plants
Food reserve
Amylose+Amylopectin

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16
Q

Describe amylose

A

Made from alpha glucose molecules
Linked by alpha 1-4, glycosidic bonds
Long helical
Unbranched, linear chain

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17
Q

describe amylopectin

A

branched molecule
Made by alpha glucose molecules
alpha 1-4 and alpha 1-6 glycosidic bonds
Branches are 1-6 linkages
Shorter chains

Majority are alpha 1-4 glycosidic bonds.

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18
Q

How can we test for the presense of starch?

A

Iodine solution
Iodine in potassium iodide solution
reacts with amylose in starch
Forms a strach-iodine complex
orange/brown🡢Dark Blue🡢Blue-Black

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19
Q

describe glycogen

A

Storage of carbohydrate in animals
Similar structure to amylopectin
Alpha glucose
1-4 and 1-6 glycosidic bonds
More branched than amylopectin
Clumped together🡢forms granules
Abundant in liver and muscle cells

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20
Q

Why does excess glucose need to be stored as starch and glycogen?

A

Glucose is soluble so can increase concentration/decrease water potential of cell.
Water would enter
Cell volume increase, animal cell may burst

It is also reactive=interfered with other reactions in the cell.

Starch and glycogen is:
Inert-non reactive
Insoluble-no osmotic effect on cell, does not diffuse easily out of cell.
Compact-large quantity of energy released when hydrolysed.
Glucose can be stored/mobilised quickly-many ends of attachement/removal of glucose.

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21
Q

Describe the function of the polysaccharide cellulose

A

Structural role in plant cell walls
High tensile strength
Prevent cell bursting
Helps stand withstand turgor pressure
Fully permeable

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22
Q

Describe the structure of polysaccharides cellulose.

A

Beta glucose
Molecules of B-glucose are rotated at 180 to each other.
beta 1,4-glycosidic bonds.
unbranched, straight chain, linear.
🡢Form fibres

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23
Q

Describe how cellulose forms fibres.

A

From molecules🡢fibres with high tensile strength
Beta Glucose🡢Cellulosemolecule🡢Microfibril🡢Fibre
1)cellulose are straight chains, can lie parallel to each other.
2)Hydrogen bonds formed between cellulose molecules. 🡢 many -OH groups in cellulose
3)Forms microfibrils and fibres
4)Fibres are arranged in a criss cross manner.
🡢many gaps between fibres
🡢cell wall is permeable to water, ions etc.

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24
Q

How can we test for carbohydrates?

A

We test for the presense of reducing and non-reducing sugars.
Reducing: All monosaccharides and Disaccharides except sucrose.

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25
Q

How can we test for the presense of reducing sugars?

A

Add 2cm3 of benedicts solution to 2cm3 of reducing sugar.
Copper (II) sulphate in alkaline solution.
Blue Colour
Reaction requires heating at 90degrees celcius.

if reducing sugar is present:
Cu2+🡢Cu+ (in benedicts solution)
Blue, soluble🡢red, insoluble

Forms brick-red precipitate (if high concentrations of reducing sugars are present)/

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26
Q

How can we test for the presense of non reducing sugars?

A

testing for the presense of non-reducing sugars (e.g sucrose)

some disaccharides such as sucrose are not reducing sugars so you would get a negative result from benedicts test. In such a case you should then carry out a test for a non-reducing sugar.

in the non reducing sugars test, the disaccharide is first broken down into its two monosacharide constituents. The chemical reaction is hydrolysis and can be brought about by adding hydrochloric acid. The consitutent monosacharides will be reducing sugars and their presense can be tested for using bendicts test after the acid has been neutralised.

Procedure
1.Add 2cm3 of sample 2cm3 of acid to hydrolyse glycosidic bonds🡢monosaccharides.
2.Heat at 90 degrees celcius
3.Neutralise using 2cm3 of sodium hydroxide.
4.Add 2cm3 of benedicts solution to the mixture
5. Heat at 90 degrees celcius.

Results:
Brick red precipiate=non redcuing sugar
even after hydrolysis remains blue colour=Not sugar.

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27
Q

Describe lipids

A

Made of carbon, hydrogen, oxygen and sometimes Phosphorus.
Important for:
1. Energy storage (lipids have many C-H bonds, can generate more-E than carbs).
2. Structural component of membranes.
3. Other specific biological functions (certain hormones are made up of lipids.

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28
Q

Describe the structure of glycerol and fatty acids..

A

Glycerol:
Has 3 carbons
3-OH groups
Functional group is a hydroxyl group.
Fatty acid
Has an acid “head” (-COOH group)+ a long hydrocarbon chain
🡢many C-H bonds.
Hydrocarbon chain is hydrophobic and non-polar.

you need to be able to draw and recognise fatty acids.

29
Q

What are the types of fatty acids?

A

saturated fatty acids.
No double bonds.

Unsaturated fatty aics
Has double bonds
Mononsaturated FA= 1 double bond
Polyunsaturated FA>1 double bond

Results in kink in hydrocarbon tail
lesser C-H bonds.
Lower melting point-liquid at room temperature.

30
Q

Describe the polymer-triglycerides

A

3 fatty acids + 1 glycerol
Linked by ester bonds
Formed via condensation reactions by removal of three water molecules (H from glycerol and OH from fatty acid).
FA can be saturated or unsaturated.

31
Q

Describe the properties of triglyceride.

A

Insoluble in water
Bcs of the long hydrocarbon tails of the fatty acid.
Non-polar, hydrophobic
Soluble in organic solvents for e.g ether, chloroform, ethanol.

32
Q

Describe the role of triglycerides:

A

1) source of energy
🡢Many C-H bonds (more than hydrocarbohydrates)
🡢Higher porportion of hydrogen
🡢Insoluble and compact
🡢more energy can be produced per unit mass

2) metabolic source of water
🡢high ratio of H to O atoms
🡢release water during fat oxidation
🡢especially for desert animals

3) Insulator
🡢 Below dermis

4) Protection of organs

5) Buoyancy
🡢blubber

33
Q

Describe the structure of phospholipids.

A

Composed of
1 glycerol
2 fatty acids
1 phosphate gp (PO4-)

May also have other groups attached to phosphate gp (represented by R).

a)They have a hydrophillic head
phospahte groups
Charged, polar
Forms h-bonds with water

2)Hydrophobic tails
Fatty acid residues
Hydrocarbon chair are insoluble and non polar
repels water

34
Q

What are the roles of phospholipids

A

1)Forms a phosphlopid bilayer
with a hydrophobic core
barrier to water-soluble substances at membrane
lipid soluble substances can pass through

2) allow regulation of membrane fluidity
Double bonds in unsaturated fatty acis tails increases fluidity
sat FA decreases fluidity

3) Helps to hold membrane proteins in place
Hydrophobic interaction with “floating” membrane proteins.

4) Can combine with carbohydrates to form glycolipids.
Important in cell recognition.

35
Q

What is the identification test for lipids?

A

Emulsion test for lipids.
1) Shake sample with ethanol
2) Pour mixture into a tube with water

Results:
Transparent-no lipids
White and cloudy-lipids present

🡢Lipid molecules clump together
🡢Forming little groups dispersed throughout the liquid
🡢Emulsion

36
Q

what are the monomers which form maltose, sucrose and lactose?

A

The three most common disacharides are maltose (alpha glucose+ alpha glucose), sucrose (alpha glucose + beta fructose) and lactose (glucose + galactose).

37
Q

Desribe proteins

A

Made of C,H,O, N (sometimes, S)
Examples of structures made of proteins
* Haemoglobin
* Collagen
* Components of cell membranes
* Enzymes
* Antibodies
* Keratin

Monomer: amino acids
Dimer: dipeptide
Polymer: Polypeptide

38
Q

Describe the general structure of amino acids:

A

H
I
HOOC-C-NH2
I
R

 amine group, carboxylic acid group and r group
39
Q

Give examples of the type of amino acids

A

The simplest amino acid is glycine
R group=H

Another onme to remember is cysteine
R group=contains sulphur (-CH2-SH)

dont need to draw only identify cysteine.

40
Q

How do proteins form dipeptides?

A

A peptide bond forms between C of -COOH and the N of -NH2.
Peptide bond is o=C-N

41
Q

How are polypeptides formed from proteins?

A

Many amino acids undergo condensation reaction will give you a polypeptide.

Many peptide bonds.
Synthesised at the ribosome.
Condensation reaction.

How to identify central carbon:
First find peptide bond and circle
The carbon atoms directly next to peptide bond are central carbons.

42
Q

What are the types of bonds in a protein?

A

peptide bonds (present in all polypeptides)

  1. Hydrogen bonds
  2. Disulfide bonds
  3. Ionic bonds
  4. Hydrophobic interactions

Arranged in order of weakest to strongest=
Hydrophobic Interactions
H bonds
Ionic bonds
Cocalent Bonds e.g. disulphide and peptide bonds.

43
Q

describe peptide bonds

A

very strong
Covalent bonds
Between C and -COOH and N of -NH2
Result of condensation reaction

present in all polypeptides.

44
Q

Describe hydrogen bonds

A

Individually weak
But many H bonds 🡢 cumulatively strong

between H of -NH/-OH group and O of -OC group
OR between R groups

easily broken by:
* High temperatures
* pH changes

45
Q

describe disulfide bonds

A

Very strong covalent bonds
Between sulphur atoms of cysteine amino acids.

46
Q

Describe ionic bonds

A

between ionized amine and carboxylic acid groups.
🡢-NH3+ and -COO-groups
🡢that are not involved in peptide bonding
* or between charged R groups
* weaker than disulphide bonds, but stonger than H bonds.
* easily broken down by pH changes and high temp.

usually at end of polypeptide chain

47
Q

Describe hydrophobic interactions

A

Between non-polar/hyrdrophobic R groups
Repel and move away from the water
Weakest

48
Q

What are the four levels of protein structure?

A

Primary structure
Secondary structure
Tertiary structure
Quaternary structure

49
Q

Describe the primary structure of protein.

A

Linear sequence of amino acids
Held together by peptide bonds
Specific sequence of amino acids
🡢Each with diff properties of R groups
🡢 Dictates folding of the polypeptide chain.

50
Q

Describe the secondary structure of proteins.

A

H bonds between amino acids.
Not located directly next to each other.
Of the same polypeptide chain

Two conformations:
1) Alpha helix
* Hydrogen bonding
* Between h atom of the -NH group and O atom of the –CO group.
* 4 places amino acid ahead
* Forms spring-like structures

2) Beta pleated sheets
* Hydrogen bonds
* Between H atom of the -NH group and O atom of the -CO group.
* straighter looser form
* Parallel, flat sheets

51
Q

Describe the tertiary structure of proteins.

A

.Coiling and folding of secondary structures.🡢into a precise 3D structure.
Due to interactions between R groups.
Only polypeptide chain only.
Could be held by all 4 bonds-H bonds, disulfide bonds, ionic bonds and hydrophobic interactions.

52
Q

Give an example of a tertiary structure protein?

A

Myoglobin
* oxygen carrying molecule
* Present in muscle cells
🡢gives it a red colour

Made of 1 polypeptide chain
Has a haem group=non amino acid group
That binds 1 molecule oxygen

53
Q

Describe quaternary structure in proteins.

A

pretty much the same as tertiary structure except:
Combination of two or more polypetide chains
Held together by all four bonds
for example collagen and haemoglobin.

54
Q

What are the two different types of proteins?

A

Globular and Fibrous proteins

55
Q

Describe globular proteins and given examples.

A

Spherical/ball shape
Mostly tertiary, sometimes quatenary structure
Soluble
More functional roles
For e.g. all enzymes, antibodies, some hormones, myoglobin, haemoglobin.

56
Q

Describe fibrous proteins and give examples.

A

Long, parallel strands
Mostly secondary structure (sometimes tertiary and quatenary) and form fibers.
Insoluble
More structural roles
For example collagen and keratin

57
Q

What makes globular proteins soluble?

A

Amino acids with non-polar/hydrophobic R groups are inside
Amino acids with polar/hydrophillic R groups face outside.

58
Q

Describe the structure of haemoglobin

A

Has quaternary structure
made of 4 polypeptide chains
2 alpha globin chains and 2 beta globin chains

Globular
Amino acids with non-polar/hydrophobic R groups are inside
Amino acids with polar
Hydrophilic R groups face outside

Each polypeptide has a haem group
Prosthetic group=non amino acid group
Permanent part of haemoglobin
Each haem has 1 iron ion (Fe2+)
Each Fe2+can bind to one oxygen molecule.
One haemoglobin can bind 4 molecules of O2

59
Q

Describe the structure of collagen

A

Structural protein
High tensile strength
Every 3rd amino acid of each collagen polypeptide is glycine.
Usually Proline-Alanine-Glycine repeat
Glycin has the samllest R group!
🡢so it can be tightly wound

  • 3 polypeptide chains form a triple helix collagen molecule.
    🡢held by hydrogen bonds.

Collagen molecules lie parallel and form covalent cross-links between R groups of Lysine.

Staggered ends so no weak points.
forms fibrils and fibres.

60
Q

Describe the test for the presense of proteins.

A

Bieuret reagent
Copper (II) sulphate and dilute potassium hydroxide.
Add 2cm3 of bieuret solution to 2cm3 of sample

Purple-protein present
Blue-no protein

NH2 groups in amine react eith copper ions🡢Purple.

61
Q

Describe the structure of water.

A

Dipole in nature
🡢O atom has slight negative charge
🡢H has slight positive charge

Hydrogen Bonding
🡢Between the O and H atoms of different water molecules.
🡢Induvidually weak, cumulatively strong.

62
Q

Why does water have a high specific heat capacity?

A
  • Specific heat capacity=amount of heat required to raise the temperature of 1kg of water by 1 degrees celcius.
  • large amount of energy need to raise the temperature of water.
    🡢Due to H bonding in water.
    🡢Large energy needed to break the hydrogen bonds..
  • Provide stable tempreature/enviroment.
    🡢Acts as a buffer against sudden temperature change.
    🡢Temperature of water does not chane quickly.
63
Q

Why does water have a high latent heat of vaporisation?

A
  • Large amount of energy needed for water to evaporate
    🡢 Due to H bonding in water
  • When water does evaporate it is able to remove a large amount of heat energy from surroundings.
    🡢Important as a cooling mechanism.
64
Q

Explain why water has a high latent heat of fusion.

A
  • Water also needed to lose a large amount of heat to freeze.
    🡢due to hydrogen bonds between water molecules
    🡢Provide stable habitat for aquatic organisms, less likely to freeze.
  • Ice is less dense than water
    Water is most dense at 4 degrees celsius
    Floats🡢acts as an isulator on surface of frozen lakes.
65
Q

explain why water can be used as a solvent.

A

water is dipolar
Dissolve ions and polar molecules for example oxygen, CO2 and ammonia.

Important for:
Transport, removal of wastes, secretios, medium for enzymatic action.

Not solvent for non-polar molcecules (lipids).

66
Q

What is cohesion and adhesion?

A

Water tends to stick to each other (cohesions) and stick to surfaces (adhesion) because of hydrogen bonds.

Useful for:
1) transport of water in xylem tissue of plants
🡢long, unbroken coloumn of water

2) High surface tension
🡢Surface dwellers habitat for e.g. pond skater.

67
Q

Name the type of polypeptide in a haemoglobin molecule that is different in sickle cell haemoglobin compared to normal haemoglobin.

A

Beta Globin

Past paper question

68
Q

Outline the affect of the change in the amine acid sequnce of a beta globin on the structure and function of haemoglobin.

A

R groups of glutamic acid is polar and R groups of valine is non polar.
Change in tertiary structure.
Change in quatenary structure of hameoglobin.
Haemoglobin is less soluble.
Haemoglobin is less effiencet and biding and transporting oxygen.

69
Q
A

A level biology-CIE (13 decks)

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