Biological molecules

Why is starch a good storage molecule?

• large - so it does not diffuse out of membranes

• compact so good for storage

• insoluble so does not affect the water potential of cells

• amylopectin is densely branched, so glucose molecules can be released quickly as enzymes can act simultaneously at branches

• when hydrolysed, forms alpha glucose, which is easily transportable, and used in respiration.

Structure of amylose

Long, unbranched chain of alpha-glucose; has a coiled structure, making it compact and good for storage

structure of amylopectin

Long, branched chain of alpha-glucose, side branches allow the enzymes that break the molecule down to access the bonds easily, meaning glucose can be released quickly

Test for starch

Iodine solution

-Positive:Blue black

-Negative:Orange yellow

how is starch held together?

OH groups form hydrogen bonds, which hold the helices together

general formula of monosaccharides

(CH2O)n

what is the structure of glucose

hexose monosaccharide

How is a dissacharide formed?

Two monosaccharides join in condensation reaction forming a 1-4 glycosidic bond

glucose + glucose

maltose + H2O

glucose + fructose

sucrose + water

glucose + galactose

lactose + water

what is the difference between alpha and beta glucose?

the hydroxyl group on Carbon 1 in beta glucose is inverted

How is a glycosidic bond broken?

A hydrolysis reaction where water is added

function of glycogen

energy storage in animals

where is glycogen found?

liver and muscles in granules

Structure of glycogen

straight chain of alpha-glucose (1,4-glycosidic bond) with side branches (1,6-glycosidic bond)

which is more densely brached, amylopectin or glycogen?

glycogen

Why is glycogen a good storage molecule?

very compact, more densely branched than starch, meaning that alpha glucose molecules can be released quickly when hydrolysed, large so does not diffuse out of membranes, insoluble so doesn't effect water potential of cells.

why is it important that glycogen is more densely branched than starch?

animals have a higher metabolic rate than plants, so require the quicker release of glucose molecules for respiration.

monomer of cellulose

beta glucose

what properties of cellulose give it strength?

- every other monomer is inverted to give it high tensile strength

- hydrogen bonds form between adjacent long straight chains.

- OH groups occur on both sides of the molecule so it can form H bonds on both sides

- chains group together to form microfibrils, which form fibres.

how does cellulose prevent the cell from bursting?

exerts inward pressure that stops any further influx of water

how does the cell wall increase the surface area for photosynthesis

makes the cells turgid by inserting inward pressure

Test for reducing sugars

Benedict's test. A blue solution, add a few drops to your solution. Heat in a water bath and if reducing sugars are present the benedict's will turn brick red

Test for non-reducing sugars

Test for non-reducing sugar

Heat with Benedict's

If negative (stays blue), hydrolyse substance with HCl and neutralise with NaOH. (or hydrolyse with an enzyme)

Heat with Benedict's Brick red precipitate indicates non- reducing sugar.

what causes the colour change in Benedicts

the reducing sugars cause Cu2+ ions to change to Cu+, which have a red colour

Results of Benedict's Test

green- very low, yellow- low, orange- medium, red- high

Role of lipids

source of energy due to high proportion of C-H bonds compared to C atoms, waterproofing- insoluble in water,

insulation, slow conductors of heat and electricity, so used as insulation around myelin sheath of nerve cells, protection of delicate organs

Why do saturated fats have higher melting points than unsaturated fats?

because there are no C--C bonds in saturated fats, so the chains are long and straight, so can pack more tightly together, so the inter molecular forces are stronger

what bond is formed in a triglyceride

ester bond

how many fatty acids bond to a glycerol molecule in a triglyceride?

3

how are unsaturated fatty acids found

as oils

why are lipids good storage molecules?

-insoluble in water- does not effect the water potential of cells

-high ratio of C-H bonds to C atoms

-high ratio of hydrogen to oxygen atoms so an important source of water

-low energy to mass ratio

how are phospholipids different from triglycerides?

one fatty acid group is swapped out for a phosphate group

which section of a phospholipid is hydrophobic and which is hydrophillic?

tail- hydrophobic, head- hydrophyllic

Why is the head of a phospholipid hydrophilic?

Due to the negatively charged (polar) phosphate group attached to the head

Why is the tail of a phospholipid hydrophobic?

the tail is composed of fatty acids, which are naturally non-polar

what do phospholipids form in a membrane and why?

form a bilayer as the hydrophobic tails face inwards to avoid the liquid cytoplasm, whilst the hydrophillic heads face out.

what is the formula of a glycerol molecule?

monomer of proteins

amino acids

How many amino acids are there?

20

what compounds are proteins and why?

amphoteric compounds becuase the amine group is basic, whilst the carboxyl group is acidic.

What elements make up proteins?

carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur

what do two amino acids form?

a dipeptide, connected by a peptide bond in a condensation reaction, which also produces water

from which groups does the water molecule formed in the condensation of amino acids come from?

H from the amine group, OH from the carboxyl group

Where does protein synthesis occur?

ribosomes

how are polypeptide chains broken?

hydrolysis reactions

What is the primary structure of a protein?

sequence of amino acids in a polypeptide chain

What is the secondary structure of a protein?

folding of chain to form alpha helix or beta pleated sheet

What is the tertiary structure of a protein?

folding of a polypeptide chain due to interactions between side chains of amino acids that lie in different regions of the primary sequence

What is quartenary protein structure?

protein consisting of more than one amino acid chain

give an example of a quartenery structure

haemoglobin

where does oxygen bind in haemoglobin?

to the Fe2+ ions contained in the haem group of haemoglobin

What bonds are in the tertiary structure?

hydrogen, ionic, disulphide

globular proteins

spherical, water-soluble proteins.

Why are globular proteins soluble?

The hydrophobic R groups clump together pushing the hydrophilic R groups to the outside of the molecule allowing them to interact with a solvent

what are the ionic bonds in a tertiary structure formed between?

between carboxyl and amino groups not involved in peptide bodning

Why are fibrous proteins insoluble?

they contain a high proportion of hydrophobic R-groups

example of globular protein

haemoglobin, insulin, enzymes

Test for lipids (emulsion test)

1. Shake the test substance with ethanol (one min).

2. Mix solution with water

Positive test = white emulsion formed as a layer on top

Negative test = stays clear

why is an emulsion formed in the emulsion test?

lipid i finely dispersed as bonds broken between molecules.

Test for protein

Buriet solution

-Positive:Purple

-Negative:No change

what is buiret made up of?

sodium hydroxide and copper sulfate

structure of collagen

triple helix

what does collagen form that makes it strong?

helixes form fibrils, which form fibres.

where and how is starch found?

in plants, in the form of granules

what is starch made up of

amylose and amylopectin

what are amylose and amylopectin polymers of?

alpha glucose

how are saturated fats usually found

as fats

What is a prosthetic group?

A non-protein component that forms a permanent part of a functioning protein molecule