Proteins (2.1.1)

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What elements do proteins contain?
Carbon, hydrogen, oxygen, nitrogen and sometimes sulphur.
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What is a polymer?
A long chain of monomers joined together to make a large macromolecule.
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What is the general structure of an amino acid?
Each amino acid is made up of an amino group (NH2), a variable R group, and an acid group (COOH).
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How do plants obtain nitrogen to make amino acids?
They take up nitrates from the soil and use the nitrogen from this to make amino acids and proteins.
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How do animals obtain nitrogen to make amino acids?
Consume protein in diet, digest it into amino acids, absorb these into the bloodstream, where they are carried to cells.
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How are amino acids joined together?
By a condensation reaction between the acid group of one, and the amino group of another. This releases a water molecule and forms a covalent bond. This new bond is a peptide bond.
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Where are proteins made?
At the ribosomes/RER. It is controlled by the DNA/genetic code in the nucleus, which instructs the ribosomes on which proteins to make.
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What is the primary protein structure?
The unique sequence of amino acids in the initial polypeptide chain produced.
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Why does the primary structure affect the final structure of the protein?
Different amino acids have different R groups which will affect how the polypeptide chain twists and folds into its final shape. Different R groups allow different bonds to form as the protein structure develops.
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Do proteins function at the primary level?
No, first they must be built up into at least the secondary structure.
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What are the two arrangements for secondary protein structure?
Alpha helix (spiral) and beta pleated sheet (zig zag).
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How is the secondary protein structure held?
They're held together by hydrogen bonds between the amino acids. The hydrogen bonds collectively hold the structure in place.
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What is the tertiary protein structure?
The alpha helices and beta sheets can be folded further to give a protein with a specific shape. These structures are held in place by several types of bond.
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What types of bond hold the tertiary structure in place?
Hydrogen bonds. Ionic bonds- between oppositely charged R groups. Disulphide bonds- One amino acid contains sulphur. When 2 cysteines are close in polypeptide strong covalent bonds form. Hydrophilic/phobic interactions.
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What are hydrophilic/hydrophobic interactions?
Some amino acids have hydrophobic R groups which stay towards the centre of the protein. Others have hydrophilic R groups and are found around the edges. Affects final shape.
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What important molecules do tertiary structures form the basis of?
Enzymes. Some hormones. Membrane proteins (channels and carriers)
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Why is the functioning of a tertiary protein greatly affected by temperature?
Temperature goes up, more k.e & molecules vibrate. The hydrogen bonds in a tertiary protein break easily. If the temperature increases a lot, all of the bonds holding structure will break. Protein loses its specific 3D shape & no longer functions.
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What is a quaternary protein?
Contains more than one polypeptide chain.
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Give an example of a quaternary protein and its structure.
Haemoglobin is made up from 4 polypeptide chains, each with an non-protein haem group- prosthetic group. It has 2 alpha and 2 beta chains.
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What are globular proteins?
Very precise shape due to hydrophilic/hydrophobic interactions. Form anitbodies, enzymes, membrane proteins and some hormones. They're often partially soluble.
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What is the function of haemoglobin?
To carry oxygen from the lungs to the respiring tissues. It is the haem group which picks up the oxygen. They have a high affinity for it when concentration is high, but release it into tissues.
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What are fibrous proteins involved in?
Providing structural strength in organisms.
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What are globular proteins involved with?
Metabolic processes in organisms.
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Where does collagen provide mechanical strength?
Makes up outer layer of artery walls. Tendons are made from collagen. Bone structure, contains collagen. Makes up cartlidge and connective tissue.
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What are fibrous proteins?
Long fibres, that are large and not water-soluble. They tend to have structural roles in the body. Eg: keratin found in hair, collagen found in skin.
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Give an example of a fibrous protein and its structure.
Collagen is a fibrous protein. Every 3rd amino acid of p.p chain is glycine- is small & allows 3 chains to fit closely together. Made of 3 polypeptide chains wound around each other. Many H-bond to make larger collagen fibrils, then collagen fibres.
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