1.1.2 Molecules

Sylabus guided notes for AS OCR Biology (Human) 1.1.2 Molecules

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1.1.2 Molecules
(a) Amino Acids
(b) Peptide Bond Formation
(c) Proteins
1. Primary structure ­ the sequence that particular amino acids are linked together is called the primary
structure of a protein. The positioning and chemical behaviour of these amino acids ultimately
determines how the polypeptide chain folds up and the final function of that protein. Altering the amino
acid types and/or sequence will change the shape and nature of the protein that forms.
2. Secondary structure ­ localised folding within a polypeptide chain form recognisable, organised
shapes. Alpha helix is a spiral shape which is stabilised by hydrogen bonding that occurs between every
fourth peptide bond in that part of the polypeptide chain. Globular proteins like haemoglobin and
enzymes possess a high degree of this type of secondary structure. Beta pleated sheet forms stiffer

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Tertiary structure ­ the overall 3D shape one polypeptide chain folds into. It is stabilised by several
types of chemical interaction : hydrogen bonding, ionic bonds, hydrophobic / hydrophilic interactions
and disulphide bridges - strong covalent bonds that form between two cysteine amino acids R groups
4. Quaternary structure ­ more than one polypeptide chain can interact to form a final protein complex
eg haemoglobin.
(d) Haemoglobin
Haemoglobin is a globular protein that carries oxygen in the blood.…read more

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Diffusion
Diffusion is the net movement of a substance from a region where it is in higher concentration to a region
where it is lower. This continues until the concentrations are evenly distribution. Small, lipid soluble
molecules can diffuse across the plasma membrane .
Facilitated diffusion requires special proteins. Proteins that are permanently open are called channel
proteins and are lined with hydrophilic amino acids. A carrier protein works when molecules bind to
them.…read more

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Water Potential in Cells
(n) Blood Sugar Testing
Suffers from diabetes mellitus must monitor their blood glucose levels carefully. This disease results
from a failure to produce enough insulin, the hormone responsible for removing glucose from the
bloodstream after a carbohydrate meal and lowering its plasma concentration to a safe level. This is
usually done using an electronic device which contains a biosensor.…read more

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The Role Of Glucose
Glucose is an example of a monosaccharide. It is a respiratory substrate meaning it can be easily broken
down by cells during cellular respiration.
(r) Glycogen Formation
When many alpha glucose molecules join together in human cells, a polysaccharide called glycogen is
formed. One glucose residue in a chain can form a glycosidic link with three different glucose molecules.
This produces a branched molecule.…read more

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Fatty Acids
(w) Phospholipids…read more

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