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Amino Acids
· Proteins are made of amino acids.
· Amino acids are made of 5 elements CHONS (carbon, hydrogen, oxygen,
nitrogen, sulfur)
· All amino acids have the same general structure ­ a carboxyl group (COOH), and
an amino group (NH) attached to a carbon atom. The difference between different
²
amino acids is the variable group (R).
· The amino group is attached by a covalent bond to a central carbon atom called
the alpha carbon.
· The R group determines the specific properties of a given amino acid (there are
20 different R groups)
· Amino acids are amphoteric; they
have both acidic and basic properties
when they dissociate in water.
· The ability to donate or receive protons
causes amino acid solutions to behave as
buffers.…read more

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Peptide Bonds
· Amino acids are linked together by peptide bonds to form dipeptides and
polypeptides.
· It is a condensation reaction, which means a molecule of water is released during
the reaction. a hydrolysis reaction
· The reverse of this reaction adds a molecule of water to break the peptide bond.
· Dipeptide (2 amino acids join together), Tripeptide (3 amino acids join together),
polypeptide (many amino acids join together).
· Proteins are made up of one or more polypeptides.
· Amino acid polymerisation to form polypeptides is part of protein synthesis. It
takes place in ribosomes.…read more

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Protein Structure
Proteins are polymers made up of amino acid monomers.
Primary Structure: Amino acid
· This is the sequence of amino acids in the polypeptide chain.
· For example in myoglobin or any other protein to carry out its specific function, it
must contain the correct amino acids arranged in a precise order.
· If only one amino acid is out of place its function may be disrupted. For example; in
haemoglobin (the main oxygen-carrying blood protein) a change in a single amino acid,
causes sickle-cell anaemia, a serious blood disorder.
Secondary Structure:
· The polypeptide chain doesn't remain flat and straight.
· Hydrogen bonds form between the amino acids in the chain. This makes it
automatically coil into an alpha () helix or fold into a beta () pleated sheet.
· Both the helix and the sheet are held together by many hydrogen bonds, which makes
them very stable and strong structures.
Tertiary Structure:
· This refers to the 3D shape of a polypeptide chain.
· The tertiary structure is held together by bonds between the R group of the amino
acids in the protein. ( more bonds form in the tertiary structure)
· The coiled and folded chain of amino acid is often coiled and folded further.…read more

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Proteins are classified into 2 main groups on the basis of their tertiary structure;
globular or fibrous.
· Globular proteins:
· They have polypeptide chains that are tightly folded to form a spherical shape.
· Many are folded so that their hydrophobic groups are on the inside of the
molecule, and the hydrophilic groups face outwards, making these proteins soluble
in water.
· The group includes enzymes, antibiotics and many hormones.
· There shape is maintained by various bonds including ionic bonds, hydrogen bonds,
disulfide bonds and hydrophobic interactions.
· Fibrous proteins:
· Consists of parallel polypeptide chains, cross-linked at intervals to form long
fibres or sheets.
· They are usually insoluble in water and physically tough.
· They include collagen (bone), silk and keratin (hair). Haem group Alpha chain
Quaternary Structure:
· Many proteins consist of more than one polypeptide chain
bonded together. The quaternary structure is the
arrangement of the of the different chains.
· For example; Haemoglobin is made of 4 polypeptide chains
2 distinct types (alpha and beta) and 4 non-protein haem
groups.
Beta chain…read more

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Protein Denaturing
· If the hydrogen bonds holding the protein in shape are broken, a process called
denaturing occurs.
· The covalent bonds in the primary structure are not broken, but the polypeptide
chains unravel and lose their specific shape.
· It can be caused by changes in pH, salt concentration or temperature.
Denaturing of a globular protein
Denaturing of a fibrous protein…read more

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