Biological Molecules

what are hydrogen bonds

Force of attraction between oppositely charged regions of neighbouring water molecules

define cohesion

Attraction between molecules of the same substance

define adhesion

attraction between molecules of different substances

properties of water

Good solvent

Can transport dissolved substances into and out of cells

Cohesive properties

Adhesive properties

high specific latent heat

high specific heat capacity

Why is water a good habitat (3)

Difference in structure between alpha and beta glucose

In alpha glucose OH below C1

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In beta glucose OH above C1

which 2 polysaccharides are in starch

Amylose and Amylopectin

How is glucose stored in plants

As starch

How is glucose stored in animals and fungi

As glycogen

Examples of monosaccharides

glucose, fructose, galactose, ribose

Examples of disaccharides

maltose, sucrose, lactose

Examples of polysaccharides

starch, glycogen, cellulose

Condensation reaction

when 2 molecules join together releasing H₂O

Hydrolysis reaction

1 water molecule required to break each bond

advantages of glucose being soluble

glucose can dissolve in cytosol of cells

can be transported in blood

Structure of alpha glucose

Structure of beta glucose

Structure of ribose

Structure of deoxyribose

Which monosaccharides make lactose

beta glucose + galactose

Which monosaccharides make sucrose

glucose + fructose

Which monosaccharides make maltose

glucose + glucose

How to use colorimeter?

(6 steps)

1. precipitate is filtered so only the blue benedicts solution remains

2. red light is shined through the solution because red is complimentary to blue light

3. a photoelectric cell measures the amount of red light transmitted through the blue benedicts solution

4. more red light is transmitted, higher the concentration of glucose

5. this is repeated with a range of known concentrations of glucose and the amount of red light transmitted is noted down

6. a calibration curve can be drawn, which can be used to work out unknown concentrations based on amount of red light transmitted

Structure of cellulose

Chain of beta glucose monomers

Each alternate monomer is flipped

Bonded with 1,4 -beta glycosidic bonds

Properties of cellulose (5)

Structure of Starch

branched molecule

made of 2 polysaccharide chains - amylose and amylopectin

Structure and properties of amylose

Structure

Unbranched

1,4 -alpha glycosidic bonds

twists to form helical structure and stabilised by hydrogen bonds

Properties

compact

insoluble

Why is amylose being insoluble an advantage

It does not affect osmotic balance of cells

Structure and property of amylopectin

Structure

branched

made of alpha glucose monomers

1-4 and 1-6 alpha glycosidic bonds

Properties

compact

glucose quickly hydrolysed

more insoluble than amylose

why is starch a good storage molecule of energy in plants (3)

insoluble so doesn’t affect osmotic balance of cell

large so cannot diffuse out of cell

compact so can store lots of glucose in small space

structure of glycogen (3)

more branched than amylopectin

made of alpha glucose monomers

1-4 and 1-6 alpha glycosidic bonds

why is glycogen a good store of glucose in animals (3)

compact

lots of free ends so glucose can be rapidly added or removed

useful as animals move around alot - high metabolic rate

where are major stores of glycogen found in animals

liver and muscle cells

how to test for reducing sugars

add sample to test tube

add equal volume benedicts reagent

heat gently in waterbath

observe colour change

why does benedicts reagent change colour in presence of reducing sugars

Cu2+ ions in benedicts are reduced to Cu+ ions

how to test for non reducing sugars

boil sample with dilute hydrochloric acid to hydrolyse into monosaccharides

add NaHCO3 to make solution alkaline

add benedicts reagent and heat in water bath

observe colour change

How to test for starch

Add few drops of iodine to sample

colour change from orange to black if positive

how does a biosensor work

proteins such as enzymes or antibodies are used to detect presence of biological molecules

what is the substance being tested in a biosensor called

analyte

3 types of lipids

triglycerides, phospholipids, sterols

structure of triglycerides

3 fatty acid molecules attached to 1 molecule of glycerol

What is a saturated triglyceride

no double bonds between carbon atoms in fatty acid tails

why is boiling point of unsaturated triglycerides lower (3)

double bond causes kinks in structure of fatty acid tails

molecules cannot pack closely together

weaker Van der Waals forces

function of triglycerides (6)

energy store

respiratory substrate

thermal insulator (blubber in seals)

protection of internal organs

aids in buoyancy (whales)

waterproofs fur (otters)

Why are triglycerides a good energy store (3)

2x more energy dense compared to same mass of glucose

due to large number of C-H bonds

insoluble so does not affect osmotic balance of cells

why are triglycerides insoluble

because nonpolar fatty acid chain does not form hydrogen bonds with water

structure of phospholipids

1 phosphate group and 2 fatty acid chains bound to 1 glycerol molecule

why is the head of phospholipids hydrophillic

due to negatively charged phosphate group

function of phospholipids (3)

cell membrane

act as emulsifiers in food

regulate cellular activities such as cell migration

how do phospholipids act as emulsifiers in food

they prevent water and oil forming seperate layers by dispersing oil droplets

name of bond between phosphate group and glycerol in phospholipids

phosphate ester bond

function of cholesterol in body (4)

regulates fluidity of cell membrane

used in liver to produce bile

used to make vitamin D

used as starting point for many hormones

what is the general structure of an amino acid

amino group (NH2), carbon, hydrogen, R-group and carboxyl group (COOH)

how is a peptide bond formed

when amino group and carboxyl group react in a condensation reaction

which enzyme catalyses formation of peptide bonds in ribosome

peptidyl transferase

what is a dipeptide

molecule formed by 2 amino acids

what is a polypeptide

molecule formed from 3 or more amino acids

what are the 4 levels of protein structure

primary, secondary, teritiary, quaternary

what is the primary structure of proteins

the specific sequence of amino acids in the polypeptide chain

what determines the primary structure of proteins

base sequence in the gene for that protein

what does primary structure of proteins affect

determines final 3d shape of protein

what is the secondary structure of proteins

either alpha helices or beta pleated sheets are formed due to hydrogen bonds forming between peptide bonds

what is the tertiary structure of proteins

interactions between R - groups of amino acids

determines final shape of polypeptide chain

what are the interactions that occur in tertiary structure of proteins

hydrophillic and hydrophobic - weak interactions between polar and non-polar R groups

hydrogen bonds - formed formed between OH groups of R groups

ionic bonds - bonds between oppositely charged R groups

disulfide bridges - covalent bonds between sulfur atoms in R groups

what is the quaternary structure of proteins

interactions between 2 or more different polypeptide chains called subunits

properties of globular proteins (3)

Soluble

roughly spherical in shape

play a metabolic role in body

why are globular proteins soluble

because they have hydrophillic R groups on the outside

Structure of haemoglobin (2)

conjugated protein made of 2 alpha and 2 beta subunits

each subunit has prosthetic haem group

which metal ion is in a haem group

Fe2+

function of haemoglobin

binds reversibly to oxygen to transport it in blood

Structure of insulin

2 subunits linked by disulfide bridges

function of insulin

regulates blood sugar levels

structure of lyzozyme

single polypeptide chain

folds to form groove on surface which is the active site

function of lyzosyme emzyme

catalyse breakdown of a molecule in bacterial cell wall

where is lyzosyme enzyme found

tears and saliva

structure of catalase

conjugated protein with 4 haem groups

function of catalase (2)

breaks down hydrogen peroxide into hydrogen and oxygen

prevents build up of hydrogen peroxide in cells

properties of fibrous proteins (4)

insoluble

play a structural role in body

long rope-like molecules

organised structure

why are fibrous proteins insoluble

have large proportion of amino acids with hydrophobic R groups

why do fibrous proteins have an organised structure

repetitive amino acid sequence in primary structure

what is collagen (2)

connective tissue found in skin, tendons, ligaments and nervous system

used for shock absorbtion

properties of collagen

strong and flexible

what is keratin

strong protein found in hair and nails

properties of keratin

very strong due to large number of disulfide bridges

what is elastin

protein found in elastic fibers in skin, walls of blood vessels, alveoli

properties of elastin

very flexible - allows elastic recoil

how to perform emulsion test for lipids

mix sample with ethanol

mix ethanol-sample solution with water and shake

look for white emulsion

why is starch compact

has lots of branches

helical shape

3 marks

describe how structure of llama haemoglobin is likely to be different from that of camel haemoglobin with reference to the four levels of protein structure (6 marks)

• difference in primary structure

• different amino acid sequence

• one amino acid changed

• amino acid change could cause change in secondary structure

• initial coiling of polypeptide change different

• different number of hydrogen bonds formed

• different arrangement of alpha helices, beta pleated sheets

• amino acid change could cause change in tertiary structure

• different 3d shapes of polypeptide chains

• ionic bonds, disulfide bridges

• amino acid change has not changed quaternary structure

• alpha and beta subunits still able to form haemoglobin in both camel and llama

2 marks

3 marks`

describe and explain how the structure and properties of different carbohydrates suit them to their role as energy storage molecules in plants and animals (6)

describe and explain how the structure and properties of lipids suit them to their role as energy storage molecules in plants and animals (4)

1 mark

Lipids less dense than protein

explain how water molecules can form hydrogen bonds with nitrate ions (NO₃^-) (2 marks)

• water molecules are polar

• nitrate ion is negatively charged

• hydrogen bonds form between H on water and O on nitrate