Biological molecules (M2)

water carbs lipids membranes

what type of molecule is water ?

polar molecule

why is water a polar molecule ?

it is a neutral molecule but has dipoles

what are dipoles in molecules ?

areas with a slight charge caused by having fewer or more electrons of different regions in the same molecule

how do water molecules bond in terms of dipoles ?

the positive ( hydrogen ) dipoles of one water molecule attract the negative dipoles (oxygen) forming hydrogen bonds

What is cohesion ?

water molecules ‘sticking tg ‘ bcs of hydrogen bonds .

Adhesion

water molecules ‘sticking’ to other molecules on surfaces because of hydrogen bonds

why is water a good solvent for ions or other polar molecules ?

the negative ions attract the positive dipoles in the water molecule while the positive ions attract the negative dipoles in the water which form hydration shells around the ions allowing the water molecules to dissolve the substances that are either ionic or polar

cohesion of water causes s____ t____

surface tension

What is surface tension?

A measure of how difficult it is to stretch or break the surface of a liquid.

How does surface tension benefit organisms?

It enables appropriately adapted organisms to use the surface of the water as a habitat.

biological consequences of water having a high shc

aquatic environments maintain a relatively stable temp throughput the year regardless of weather temps making them hospitable habitats for life

biological consequences of water having a high latent heat of vaporisation

plants and animals can lose excess heat energy by evaporation of water from their surfaces e.g transpiration or sweating which allows them to maintain a stable body temp

what are monosaccharides give 4 examples and what they have in common 

single sugar molecule e.g. alpha/beta glucose fructose galactose all hexose sugars

what are pentose /hexose sugars

pentose contain 5 Carbons while hexose contains 6

disaccharide

two monosaccharides linked covalently by a glycosidic bond

what type of glucose is this and how do u know

alpha glucose the OH on the right side is on the bottom not the top 

what is this

ribose -pentose monosaccharide

what is this

deoxyribose - pentose monosaccharide

what molecule is this ?

galactose 

what is this ?

fructose

what two monosaccharides make up lactose ?

beta glucose and galactose with a beta 1-4 glycosidic bond 

what two monosaccharides make up maltose

two alpha glucoses with an alpha 1-4 glycosidic bond

which monosaccharides make up sucrose ?

alpha glucose and fructose with an alpha 1-2 glycosidic bond (as the fructose is flipped)

how do yk if a bond is alpha or beta ?

alpha bond points downwards beta points upwards 

what are the three hexose monosaccharides and why are they all soluble in water ?

glucose fructose and galactose which are all structural isomers .

they’re all soluble in water bcs they have OH grps which form hydrogen bonds w/ water molecules  

what are isomers

molecules that have the same molecular formula but differ in their structural arrangement, leading to different properties and functions

glycosidic bond 

covalent bond joining 2 monosaccharides 

condensation reaction

removal of water to form a bond

hydrolysis

addition of water to break a bond

disaccharide

2 monosaccharides joined tg by a glycosidic bond

how are the structural features of glucose related to its functions ?

5 OH grps so… :
-high solubility in water / transport in the blood or phloem

-chemically reactive -can be oxidised to release energy

OH grps ring structure means :

-it forms polymers w/ other glucose molecules

-OH grps can condense to form glycosidic bonds

a and b isomers : 

-form polymers w/ diff roles 

-a glucose = energy storage 

-b glucose = structural 

how are disaccharides hydrolysed ?

by digesting each disaccharide using its specific hydrolytic enzyme (maltose , lactose and sucrase e.g. in our digestive systems ) or by heating in acid

what is this ?

the polysaccharide amylose

consists of long chains of alpha glucose joined by 1-4 glycosidic bonds

coils up into a helix held tg by hydrogen bonds

insoluble due to its coiled structure preventing osmosis

makes up 20-30% of starch grains

only poly detectable by iodine which becomes trapped inside the long coil forming blue/black colour

what is this ?

polysaccharide amylopectin

large molecule 10-100k a glucose units

makes up 70% of starch grains 

consists of chains of a glucose linked by 1-4 glycosidic bonds with  alpha 1-6 glycosidic bonds forming branches every 25-30 glucose residues

significance of branching in amylopectin ?

glucose molecules can be hydrolysed frm the free ends of each branch 

so more branches means more glucose can be released for respiration 

what is this ?

the polysaccharide glycogen

alpha glucose storage molecule of animal cells 

more branches than amylopectin bcs animals need more energy so more glucose needs to be released at a time 

chains o alpha glucose joined by alpha 1-4 glycosidic bonds with alpha 1-6 glycosidic bonds forming branches every 10-12 glucose residues 

how is glycogen stored

stored in cells as glycogen granules

-30-50k a glucose monomers surrounding a core protein called glycogenin 

more branches makes it compact so more energy can be stored in a smaller volume 

what are the features of a good storage molecule ?

compact- doesn’t take up too much space in a cell

insoluble-cant dissolve in water then be lost in cells

no osmotic effect - doesn’t pull water into cells by osmosis 

easily hydrolysed - releases glucose when needed for respiration 

what is this ?

cellulose 

polymer of B glucose monomers joined by 1-4 beta glycosidic bonds to form  straight unbranched chains 

every 2nd glucose must be flipped 180 degrees 

individual chains are held tg by hydrogen bonds to form microfibils which bond tg to form fibres

fibres r laid down in diff directions to form a cell wall 

cellulose has high tensile strength - means it can resist a large pulling force w/o breaking 

reducing sugar test

add benedict’s reagent to sugar solution

heat in a boiling water bath for 5 mins 

-sugars w/ aldehyde or ketone grps reduce Cu2+ ions in benedicts solution to Cu+ which forms brick red precipitate 

what are the reducing sugars

all hexose monosaccharides ( glucose fructose galactose) as they can all open up to form straight chain aldehyde or ketone 

the disaccharides lactose and maltose can open up one of their rings - so r also reducing sugars 

results for sugar test

blue green - low conc

brown / orange - med conc 

brick red - high conc 

why is sucrose a non reducing sugar ?

bcs C1 of A glucose and C2 of fructose form the glycosidic bond neither of the two rings can open up 

the glycosidic bond must first be hydrolysed to form its two monos 

test for non reducing sugars

add benedict’s reagent and boil for 5 mins - neg result

add HCL to sugar solution and boil for 5 mins 

neutralise w/ sodium hydrogencarbonate 

add benedict’s reagent and boil for 5 mins 

what are lipids?

macromolecules containing the elements carbon hydrogen and oxygen

what are the different functions of lipids ?

energy storage 

thermal insulation

protection

membrane structure

electrical insulation

steroid hormones

why are lipids used as energy stores ?

they contain more energy per gram than any other type of food molecule

how are lipids used for thermal insulation ?

subcutaneous deposits of adipose tissue prevent heat loss 

how are lipids used for protection

adipose tissue cushions internal body organs

what is the role of lipids in membrane structure?

all biological membranes are made from phospholipids

what is the role of lipids in electrical insulation?

nerve fibres are surrounded by a fatty myelin sheath

what is the role of lipids in steroid hormones ?

they’re all made of the lipid cholesterol

how are triglycerides formed

by the condensation reaction of 1 glycerol and 3 fatty acids 

what are the two types of fatty acids and compare them 

saturated : 

more common in animals 

high mps make them solid at room temp e.g. lard 

no double bond bcs molecules is saturated w/ hydrogen atoms

unsaturated:

more common in plants

low mps make them liquid at room temp

do contain double bonds bcs molecule is not saturated w/ hydrogen atoms

explain how triglycerides form by condensation reactions ?

a glycerol has 3 OH grps

each one of its OH groups interact with that of a fatty acid leading to the formation of three water molecules and three ester bonds

triglycerides consisting of saturated vs unsaturated fatty acid tails

saturated: 

pack tighter 

higher mp 

less fluidity 

tallow / lard 

unsaturated : 

packs less closely bcs of kinks 

lower mp 

more fluidity 

olive oil 

two types of unsaturated fatty acids

polyunsaturated - more than one double bond

monounsaturated - one double bond 

describe the role of phospholipids 

they naturally form a bilayer 

hydrophilic phosphate head grps make contact w/ water on the inside and outside 

hydrophobic fatty acid tails cluster tg away frm water in the middle 

structure of phospholipids

1 phosphate group - neg charge so water soluble( hydrophilic )

1 glycerol 

2 fatty acids form the tail (being  uncharged and non polar makes them water repelling (hydrophobic) ) 

what are phospholipids ?

modified triglycerides that contain the element phosphorus as well as Carbon hydrogen and oxygen

one of the fatty acids chains in a triglyceride molecule is replaced with a phosphate grp to make a phosphate lipid  

describe the structure of cholesterol 

central sterol nucleus made of 4 HC rings (found in all steroid hormones )

HC tail 

hydroxyl grp

what are sterols ?

another type of lipid found in cells . complex alcohol molecules based on a four C ring structure with an OH grp at one end e.g. cholesterol  

describe the functions of cholesterol

to maintain stability and regulate the fluidity of cell membranes

precursor for the synthesis of steroid hormones , bile acids and vitamin D 

how does cholesterol form part of the cellular membrane ?

makes membranes less fluid (it holds the phospholipids tg so they dont move as much )

OH grp sits between the phosphate head grps and the rest of cholesterol is hydrophobic so sits w/ the fatty acids

effect of cholesterol in the phospholipid bilayer

tighter packing 

incs mp

decreases fluidity

test for lipids

dissolve the sample in alcohol and mix well

pour the alc into water 

if a lipids present a milky white emulsion forms