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Summary A Level Biology AQA Biological molecules (Unit one) revision notes

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Condensed notes for unit one of AQA A Level Biology specifically on biological molecules

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Biological molecules :


Carbohydrates Polysaccharides - - disaccharides -> monosaccharides
Examples : Glucose , fructose , galactose ↳ sucrose

join to create
Glucose :
Alpha + Bet a + lactose di +
poly by a

Alpha : Beta : + mal lose condensation
CH2OH CH2OH reaction
H
I
c -
o I
H H
I
c -
o I
OH ↳ forms a


Y Y
-
bond
-


COH
1 H
H
S
COH
H
H glycosidic
oH -C oH' d
I
c OH
I I
- -
C H
it di it di
Disaccharides :


Maltose >
-


glucose-glucose
Sucrose - glucose + fructose
Lactose >
-

glucose +
galactose

To break polysaccharides/disaccharides apart ,
a hydrolysis reaction
occurs to break the bonds using water


Starch (main energy storage :
plants) :

↳ when the plant needs energy , starch is broken down
to release glucose
Starch Amylose :
+
Amylopectin
Amylose :



Long , unbranched chain Calpha-glucose) ,
coiled structure
The coiled structure makes it compact so good for storage
Amylopectin :



Long branched,
chain (alpha-glucose) , side branches/many
terminal ends

enzymes can break glycosidic bonds easily to release glucose
quickly

Starch is insoluble in water + doesn't affect water potential so
doesn't affect osmosist water can't enter the cell , making it swell
So it's good for storage

Glycogen (main energy storage : animals) :


Animals store excess glucose as glycogen
Similar structure to amylopectin but has a lot more terminal
branches so more energy released quickly
Compact so good for storage

Cellulose :
Long unbranched chain
, (beta-glucose) , straight
Chains are linked by hydrogen to form microfibrils and
macrofibrils

, Proteins :

-
Quaternary >
-

Tertiary -
Secondary >
-

Primary

Quaternary Multiple polypeptide chains
-


Tertiary -> further folding formation of hydrogen ionic , , , disulphide bridges
Secondary -> Formation of hydrogen bonds to form alpha helices +


beta-pleated sheets
primary Sequence >
-
of amino acids in the polypeptide chain joined by
peptide bonds


Fibrous proteins :
Globular proteins :


Cross links from hydrogen bonds very compact
Repetitive amino acids Roughly spherical
Little/no tertiary structure e g
.
pepsin
.




Insoluble in water because of R groups


Lipids :


non-polar ,
hydrophobic , provide source of energy
uses/properties :


Energy supply -
can be oxidised
Structural components (cell membrane (
Waterproofing (insoluble lipids (
Insulation -
help retain heat
Protection (delicate organs surrounded by layer of fat)

Triglycerides :
Fatty acids :


↳ three latty acids + one glycerol ↳ RCOOH
Can change in length

-
o
11
-
ester bond Saturated + Unsaturated
H 0 C R
↓ ↓
- -
-
,


I
O
I
c 0 C R2 >
triglycerides Maximum No maximum
-

H -
- - -




G
I 11 formed by number of number
H - c -
0 -
C -

Rs esterification hydrogen At least one C = C

it bonds Chain kinks
Noc = C


Phospholipids :


Acts as part of the phospholipid
0 -
R -
phosphate bilayer
I
group
-
> A barrier to water soluble
0 = D -
0-
I
Chydrophilic molecules

HH O
+
polar ( Make the membrane more fluid
I I I

H- C- C -
C -
H

!' I
c 0 = = o
>
-


fatty acids
R Chydrophobic
+
non-polar (

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