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A level Biology > 2.2 biological molecules > Flashcards

2.2 biological molecules Flashcards

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1
Q

How do hydrogen bonds form between molecules?

A

Water is polar as oxygen is more electronegative than hydrogen so attracts electrons in covalent bonds and forms slightly negative O and slightly positive H

There are intermolecular forces of attratction between the lone pair of Os- and Hs+ on an adjacent molecule

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2
Q

state 7 biologically important properties of water

A

high specific heat capacity
high specific latent heat of vaporisation
high boiling point
high surface tension
solvent
density
liquid

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3
Q

Why is the cohesion and surface tension nature of water important for organisms?

A

The surface of water has the ability to resist force applied to it due to the hydrogen bonds causing the water molecules to be more attracted to other water molecules than air molecules.
Due to this insects like pond skaters can walk on water and water is able to be pulled up the xylem tissue from the roots lowering demand on on root pressure and slows water loss due to transpiration in plants.

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4
Q

Explain why ice floats on water and why this is important.

A

Ice is less dense than water because h-bonds hold molecules in fixed positions further away from each other.

The ice insulates water in arctic climates so aquatic organisms can survive and move and oxygen/ nutrients/gamete can still move. Water acts as a habitat.

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5
Q

Why is water an important solvent for organisms?

A

Polar universal solvent and transports charged particles involved in intra and extracellular reactions e.g. PO4 3- for DNA synthesis

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6
Q

Why are the high specific heat capacity and latent heat of vaporisation of water important for organisms?

A

Acts as a temperature buffer and resists fluctuations in core temperatures to maintain optimum enzyme activity
Cooling effect when water evaporates from skin as sweat.

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7
Q

Define monomer and polymer and give some examples

A

Monomers are smaller units that join together to form larger molecules e.g. monosaccharides such as galactose and ribose
Polymers are made of joined monomer units for example DNA

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8
Q

What happens in condensation reactions?

A

A chemical bond forms between 2 molecules and a water molecule is produced

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9
Q

What happens during a hydrolysis reaction?

A

A water molecules is used to break a chemical bond between 2 molecules for example peptide bonds in proteins.

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10
Q

Name the elements found in carbohydrates lipids proteins and nucleic acids

A

carbohydrates + lipids = C,H,O
proteins= C,H,O,N,S
nucleic acids = C,H,O,N,P

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11
Q

Draw the structure of alpha and beta glucose

A

They are both hexose monosaccharides (6c) with a ring structure
CH2OH
I
H C——-O ( H)
I / \ I
IC OH H CI alpha glucose
I \ I I / I
HO C——-C (OH)
I I
H OH

CH2OH
I
H C——-O (OH)
I / \ I
IC OH H CI beta glucose
I \ I I / I
HO C——-C ( H)
I I
H OH

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12
Q

Describe the properties of alpha glucose.

A

Small and water soluble making it easily transported in the bloodstream
energy source and component of starch and glycogen which act as energy stores

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13
Q

describe the role of beta glucose

A

energy source and component of cellulose which provides structural support in plant cell walls

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14
Q

What types of bonds form when monosaccharides react?

A

(1,4 or 1,6) glycosidic bonds

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15
Q

Name 3 disaccharides and how they form.

A

Condensation reaction between 2 monosaccharides
maltose = glucose + glucose
sucrose= glucose + fructose
lactose glucose + galactose
all have the molecular formula c12h22011

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16
Q

Describe the structure and function of starch.

A

Storage polymer of alpha glucose in plant cells
insoluble so it has no osmotic effect on cells and is large so it does not diffuse out of cells
Amylose =
1.4 glycosidic bonds and is a helix with intermolecular h bonds making it compact

Amylopectin =
1.4 and 1.6 glycosidic bonds and is branched with many terminal ends for hydrolysis into glucose

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17
Q

Describe the structure and function of glycogen.

A

Main storage polymer of alpha glucose in animal cells
It contains both 1-4 and 1-6 glycosidic bonds and is branched with many terminal ends for hydrolysis
It is also insoluble and compact.

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18
Q

describe the structure and function of cellulose.

A

It is found in plant cell walls and is a tough, fibrous and insoluble substance. It is a homopolysaccharide made up of long chains of beta glucose bonded together by a condensation reaction with strong beta 1-4 glycosidic bonds (Every other molecule is inverted making the chains linear)

Hydrogen bonding between the rotated B glucose molecules in different chains gives the whole structure additional strength.

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19
Q

Describe the hydrogen bonds in cellulose.

A

The hydroxyl group on carbon 2 sticks out enabling hydrogen bonds to be formed and the chains run parallel with h bonds between like a brick wall

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20
Q

describe micro and macrofibrils

A

When 60-70 cellulose chains are bound together they form microfibril and these then bundle together (around 400) to form macrofibrils which are embedded in pectins and run in all directions criss crossing the wall for extra strength

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21
Q

Why is cellulose a good material for plant cell walls?

A

high tensile strength
and macrofibrils cross for extra strength but gaps are left allowing water and mineral ions to pass making it fully permeable.
Prevents the cell from bursting when turgid

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22
Q

What are some uses for cellulose

A

cotton and paper and rayon.

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23
Q

How do triglycerides form?

A

Condensation reaction between 1 molecule of glycerol and 3 fatty acids which forms ester bonds.

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24
Q

What are the differences between saturated and unsaturated fatty acids?

A

Saturates contain ONLY SINGLE BONDS and form straight chain molecules and have a higher melting point making them solid at room temperature and are usually found in animal fats.

Unsaturated contain DOUBLE CARBON BONDS C=C creating kinked molecules and have a lower melting point so theyre liquid at room temperature and are usually found in plant oils.

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25
Q

Relate the structure of triglycerides to their function.

A

they have a high energy to mass ration so hey have a high calorific value
They are an insoluble hydrocarbon chain and a slow conductor of heat (thermal insulation)
less dense and can create buoyancy for aquatic animals

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26
Q

Describe the structure and function of phospholipids

A

They have a glycerol backbone attached to 2 hydrophobic fatty acid tails and a hydrophilic polar phosphate head

Forms a phospholipid bilayer in water so it is a component of membranes

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27
Q

Are phospholipids and triglycerides polymers

A

NO theyre macromolecules as they are not made from a small repeating unit.

28
Q

Describe the structure and function of cholesterol

A

steroid structure of 4 hydrocarbon rings
adds stability to cell surface phospholipid bilayer by connecting molecules and reducing fluidity.
hormones

29
Q

What are the three types of lipids?

A

Triglyceride- energy source/store
phospholipids- membranes phospholipid bilayer
Cholesterol - membrane fluidity and hormones.

30
Q

What is the general structure of an amino acid?

A

COOH carboxylic acid group
R variable group
NH2 amine / amino group

31
Q

How do polypeptides form?

A

Condensation reaction between amino acids form peptide bonds
(-CONH-)

32
Q

Define primary and secondary structure of a protein

A

primary - sequence number and type of amino acids in the polypeptide determined by sequence of codons on mRNA
Secondary - hydrogen bonds form causing the molecule chain to either fold or coil

33
Q

Describe the 2 types of secondary structure.

A

alpha helix
All N-H bonds on the same side of protein chain
spiral shape
H-bonds parallel to helical axis

beta pleated sheet
N-H &C=O groups allternate from one side to the other

34
Q

Define the term tertiary structure of a protein.

A

3D structure of the protein molecule formed by further folding

35
Q

What are the bonds present in the tertiary structure of a protein?

A

Disulfide bridges
ionic bonds
hydroen bonds
Hydrophobic interactions

36
Q

Describe disulfide bridges

A

Strong covalent bonds between the amino acid cysteine S-S

37
Q

Describe ionic bonds

A

relatively strong bonds between charged R groups

38
Q

describe hydrophobic interactions.

A

Hydrophobic r groups tend to associate in the centre of the polypeptide whereas the hydrophilic associate on the periphery

39
Q

Define quaternary structure of a protein

A

Functional proteins may consist of more than one polypeptide and it is a precise 3D structure held together by the same bonds as the tertiary structure

May involve additional prosthetic groups.

40
Q

Describe the structure and function of globular proteins.

A

Spherical and compact and hydrophilic R groups face outwards making them water soluble and are involved in metabolic processes e.g. enzymes such as amylase

41
Q

Describe the structure of haemoglobin.

A

Globular conjugated protein with 2 A and 2B chains with 4 prosthetic haem groups (Fe2+ which binds reversibly to oxygen) and is water soluble so dissolves in plasma.

42
Q

Describe the structure and function of fibrous proteins

A

Long insoluble molecules due to a high proportion of hydrophobic r groups and can form long chains or fibres.
Useful for structure and support

43
Q

Why is collagen suited to its function

A

3 polypeptide chains in a helix structure and is glycine rich (1/3) making it small and compact
Held together by hydrogen bonds and is a component of bones, cartillage connective tissue and tendons

44
Q

How is elastin fit for purpose?

A

It is a protein with a quaternary structure made from linking tropoelastin making a large insoluble cross-linked structure
provides elasticity to connective tissue, arteries, skin, lungs, ligaments

45
Q

How is keratin fit for purpose

A

Has a large proportion of cysteine resulting in many disulphide bridges forming strong insoluble inflexible material used as a structural component of hair nails claws and hooves.

46
Q

Define conjugated protein and give examples

A

Contain a non-protein element called a prosthetic group e.g catalase and haemoglobin

47
Q

Describe the structure and function of catalase

A

Globular Protein with a quaternary structure containing 4 prosthetic groups (Fe2+) allowing catalase to interact with hydrogen peroxide to speed up it break down

48
Q

describe how to test for protein in a sample

A

Biuret test confirms the presence of a peptide bond
1 add equal volumes of biuret reagent to the sample and a positive result would be a change in colour from blue to purple

49
Q

describe how to test for lipid in a sample

A

dissolve the solid sample in ethanol and add an equal volume of water a positive result will be a milky white emulsion

50
Q

describe how to test for reducing sugars

A

Add an equal volume of benedicts reagent to the sample and heat the mixture in a water bath and a positive result is a colour change from blue to brick red

51
Q

Describe the benedicts test for non-reducing sugars

A

hydrolyse non reducing sugars e.g. sucrose into their monomers by adding 1cm3 of HCL and heating in a water bath. Then neutralise the solution using sodium carbonate solution and continue the bendicts test as usual.

52
Q

describe the test for starch.

A

Add iodine and a positive result is a colour change from orange to blue-black

53
Q

state the role and chemical symbol of hydroxide and phosphate ions

A

OH- ions affect pH and can interact with bonds in tertiary protein structure to cause denaturation

PO4 3- is a component of ATP/ADP for energy release and NADP

54
Q

State the role and chemical symbol of sodium, potassium ions

A

Na+ = affects absorption of carbohydrate in small intestine and water in kidney
K+ = generates healthy leaves and flowers in flowering plants
They both control water level of bodily fluids and pH maintenance
Contribute to nervous transmission and muscle contractions

55
Q

What is the formula and function of calcium ions

A

Ca2+
Increases rigidity of bones, teeth and exoskeleton of crustaceans.
Important in blood clotting and muscle contraction
regulates transmission of nerve impulses
Regulates permeability of cell membranes

56
Q

What is the formula and function of hydrogen ions?

A

H+
Involved in photosynthesis and regulation of blood pH
Also involved in CO2 and O2 transportation in blood

57
Q

What is the function and formula of ammonium and nitrate ions?

A

NH4+
NO3-
Maintenance of blood pH
Component of nucleic acids, vitamins, chlorophyll and the nitrogen cycle.

58
Q

What is the function and formula of hydrogen carbonates?

A

Blood pH regulation and transport of CO2 in and out of blood.

59
Q

What is the stationary and mobile phase in chromatography?

A

Stationary - chromatography paper or TLC plate
Mobile- solvent

60
Q

How does chromatography work?

A

The speed at which molecules move along the paper depend on their solubility in the solvent.

Exposed -OH groups on the surface of the paper make it very polar and allow it to form hydrogen bonds with the molecules alongside other dipole interactions.
A highly polar solute will tend to stick to the surface and move more slowly (adsorbed) whereas a non-polar solute will move up the paper very quickly.

61
Q

How is chromatography used?

A

Monitor the progress of reactions
Drug testing in urine samples.
Drug analysis for purity
Analysis of food to search for contaminants

62
Q

What do you do if the molecules are colourless and you cannot see the end result of the chromatography?

A

UV light
Ninhydrin
Iodine

63
Q

How does UV light help in a chromatography PAG?

A

TLC plates usually have a chemical which fluoresces under UV light and by shining it the paper will glow except for where the spots have travelled.

64
Q

How does ninhydrin help in a chromatography PAG?

A

Allows us to see amino acids by allowing the plate to dry then spraying some ninhydrin which binds to amino acids making them visible as brown or purple spots.

65
Q

How can Iodine help a chromatography PAG?

A

Allow the plate to dry and place in an enclosed container with a few iodine crystals. The iodine forms a gas which binds to the molecules in each spot

A level Biology (25 decks)

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