Proteins

What are proteins made from?
They are polymers of long chains of amino acids.
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What are the structures of amino acids?
They have an amino group on one end (-NH2) and a carboxyl group at the other (-COOH) and an R group in between, bonded to the central carbon.
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What is the R group?
It is different in every amino acid. It can be simple or complicated; small or large and can have different charges and polarities (some can be hydrophobic and some hydrophilic).
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What are the main functions of proteins?
They can be structural compnents (e.g. muscle is made of protein); they form enzymes, antibodies and some horomones; they can form channels and carriers in the plasma membrane to allow active transport and facilitated diffusion.
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What does it mean to say that amino acid is proteinogenic?
It means they can form proteins. Only 20 of the over 500 different types of amino acids are proteinogenic.
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What are the covalent bonds that join amino acids together called?
Peptide bonds.
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What do protease enzymes in the intestines do?
Break peptide bonds during digestion. They also break down protein hormones so that they don't have permanent effects.
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What is the primary structure of a protein?
The sequence of amino acids in a protein chain. The number and order of the amino acids is very important as just one change in this can change the function of the protein.
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What is the secondary structure of a protein?
How an amino acid chain coils or folds. Some coil into an α-helix and others a β-pleated sheet. Some don't adopt any regular structure of have different ones at different ends of the chain.
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Describe the structure of an α-helix coil.
It is held together by hydrogen bonds between the -NH group of one amino acid and the -CO group of one four ahead. There are 36 amino acids per 10 turns.
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Describe the structure of a β-pleated sheet.
Hydrogen bonds between the -NH group of one amino acid and the -CO group of another further down hold the sheet's shape.
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What is the tertiary structure of proteins?
When the secondary structure of the protein itself begins to fold, forming a precise 3D shape that's held together with bonds between amino acids that lie close to each other.
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What is the quarternary structure of a protein?
How SEVERAL polypeptide chains are arranged to make the complete protein.
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How are hydrogen bonds formed in proteins?
Most are between the amino and the carboxyl groups of different amino acids but R groups can also be involved if they are polar.
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How are ionic bonds formed in proteins?
Between parts of the polypeptide chains with opposite charges. + and -.
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What are disulfide links?
Strong covalent bonds between the R groups of two cysteines (a type of amino acid) because they contain sulfur.
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How do hydrophobic and hydrophilic interactions affect the structure of a protein?
The hydrophobic parts of R groups tend to associate together in the centre of a polypeptide to avoid water and the hydrophilic parts are usually found on the edge to be close to water. This causes the amino acid chain to twist, affecting structure.
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What is a fibrous protein?
They have regular and repetitive structures of amino acids. They are usually insoluble in water. These features mean they form fibres and tend to have structural functions.
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What is a globular protein?
Tend to be almost spherical with hydrophilic R groups on the surface and hydrophobic turned inwards. This makes them soluble in water. They usually also have very specific shapes which means they form enzymes, hormones and haemoglobin.
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What is collagen?
A FIBROUS protein that provides mechanical strength.
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Where does collagen provide mechanical strength in our bodies?
A layer in the artery walls helps withstand pressure; tendons are made of collagen; bones are made from collagen reinforced with calcium phosphate; cartilage and connective tissue is made from collagen.
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What is Elastin?
A FIBROUS protein that is strong and extensible so that it can help areas stretch and adapt its shape.
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Where does elastin function in our bodies?
Skin is stretchy and can adapt its shape because of elastin; lungs can inflate and deflate because of elastin; elastin helps our bladder expand for urine; elastin in blood vessels allows them to stretch and recoil, maintaining the pressure.
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What is haemolglobin?
A GLOBULAR protein whose quarternary structure is two α-globin chains and two β-globin chains. On the outside of each chain there is haem group (which contains an iron ion) which is a prosthetic group.
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What is a prosthetic group?
An essential part of the protein molecule that is needed for its function but is not made of amino acids.
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What is the function of haemoglobin?
In the lungs, the iron of each haem group binds to an oxygen molecule and this is how oxygen is transported in the blood.
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What is insulin?
A GLOBULAR protein that is made of two polypeptide chains. Chain A begins with a section of α-helix and the B chain ends with a section of β-pleat. Both chains fold into a tertiary structure and then joined together with disulfide links.
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What makes insulin soluble in water?
The amino acids with hydrophilic R groups are on the outside of the molecule.
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What is the function of insulin?
A hormone that binds to the glycoprotein receptors on the outside of muscle and fat cells which increases their uptake and rate of consumption of glucose.
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What is pepsin?
An enzyme that digests protein in the stomach made of a single polypeptide chain folded into a symmetrical tertiary structure held together with hydrogen bonds and two disulfide bridges.
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Why does the acidic environment of the stomach not affect the structure of pepsin?
Because only 4 R groups are basic and 43 are acidic so there are very few basic R groups to accept H+ ions and therefore there can be little effect on its structure.
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Other cards in this set

Card 2

Front

What are the structures of amino acids?

Back

They have an amino group on one end (-NH2) and a carboxyl group at the other (-COOH) and an R group in between, bonded to the central carbon.

Card 3

Front

What is the R group?

Back

Preview of the front of card 3

Card 4

Front

What are the main functions of proteins?

Back

Preview of the front of card 4

Card 5

Front

What does it mean to say that amino acid is proteinogenic?

Back

Preview of the front of card 5
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