biology - proteins

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what percentage of the body is made up of protein?
15%
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what does protein form in terms of appearance? (6)
skin, hair, nails, horns, claws, feathers
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what does protein form inside the body? (3)
antibodies (protection from disease), enzymes (metabolism and digestion), hormones (control various body systems)
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what do they allow to happen? (3)
muscle fibres to contract, help clot blood, transport oxygen in form of haemoglobin
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how do they differ from lipids and carbohydrates?
all contain nitrogen, many contain sulfur; contain carbon, hydrogen, and oxygen like the other two
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what are proteins made up of?
amino acids; small monomer units joined by condensation reactions
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how many different types of naturally occurring amino acids are there?
20
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what is the general formula for amino acids?
an amino group (-NH²) and a carboxyl group (-COOH) attached to carbon atom
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what is the R group?
differs with each amino acid; where sulfur and selenium found in some amino acids, structure of R group affects bonding (if R is polar or not)
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where do the amino acids bond?
amino group of one acid and carboxyl of another, R group not involved
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what is the name of the bond between amino acids?
peptide bond; strong
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what is the result of a peptide bond between two amino acids?
a dipeptide
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what is a chain of amino acids called?
a polypeptide chain
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how does one polypeptide contribute to a protein?
when polypeptide coils, folds, or associates with other polypeptides, it forms a protein
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how are hydrogen bonds formed between amino acids?
tiny negative charges on oxygen of carboxyl group attract tiny positive charges on hydrogen atoms of amino group when close together
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why are hydrogen bonds useful? (3)
-weak, but very common as can form between any two amino acids positioned correctly -break easily and reform if pH or temp. conditions change -important in folding and coiling of polypeptide chains
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what is a disulfide bond?
strong covalent bond formed as result of oxidation reaction between sulfur groups in cysteine or methionine molecules (amino acids) which are close together in polypeptide structure
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why are disulfide bonds useful? (2)
-much stronger than hydrogen bonds, occur less often -important for holding folded polypeptide chains in place
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what are salt bridges?
ionic bonds formed deep within protein molecule side chains; between strongly positive and strongly negative amino acids
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why are salt bridges useful?
strong, but not as common as disulfide and hydrogen bonds
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what is keratin?
protein which makes up hair and nails
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how does breaking hydrogen bonds affect hair styling?
blow drying or straightening hair breaks hydrogen bonds and reforms them temporarily until hydrogen bonds reform in original place
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how does breaking disulfide bonds affect hair styling?
perming breaks disulfide bonds between polypeptide chains and reforms them in different place permanently until hair is cut
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what are the four stages of protein structure?
primary, secondary, tertiary, quaternary
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what happens in the primary structure?
linear sequence of amino acids in a polypeptide chain
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what type of bond is involved in the primary structure?
peptide bonds
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what happens in the secondary structure?
arrangement of polypeptide into a regular, repeating structure. example is α helix (right-handed helix) which is a spiral coil or β-pleated sheet. if no secondary structure, polypeptide forms random coil
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what type of bond is involved in the secondary structure?
hydrogen bonds
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what is an example of proteins in the secondary structure?
fibrous proteins; e.g. collagen
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what happens in the tertiary structure?
3D organisation of polypeptides held by bonds, folded further into complex shapes
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what type of bonds are involved in the tertiary structure?
ionic, disulfide, hydrogen
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what is an example of proteins in the tertiary structure?
globular proteins; e.g. haemoglobin and enzymes
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what happens in the quaternary structure?
3D organisation of more than one tertiary polypeptide
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what is an example of proteins in the quaternary structure?
enzymes and haemoglobin
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what condition changes might affect the 3D shape?
temperature, pH cause bonds to break
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what is it called when changes in conditions affect protein shape?
denaturing
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what are some fibrous protein characteristics? (3)
-long, parallel polypeptides with occasional cross-linkages which form fibres -insoluble in water -very tough
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where are fibrous proteins found? (4)
-in structure of connective tissue in tendons and the matrix of bones -structure of muscles -forms silk in spiders' webs and cocoons -keratin in hair, nails, claws, feathers, horns
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what is collagen?
strong fibrous protein with triple helix structure
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what does collagen do?
gives strength to tendons, ligaments, bones, and skin
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what percentage of body protein is collagen?
35%, most common structural protein in animals
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how is collagen so strong?
has tensile strength comparable to steel due to structure of triple helix of polypeptides (each 1000 amino acids long)
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what is the primary structure of the three α chains?
repeating sequences of glycine and two other amino acids (usually proline or hydroxyproline) arranged in triple helix
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how is the triple helix held together?
large number of hydrogen bonds
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what is another reason why collagen is so strong?
collagen fibres often found combined with bone tissue, giving it tensile strength comparable to steel rods in reinforced concrete
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what is the genetic disease osteogenesis imperfecta?
triple helix not formed properly so bones brittle and break easily
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what are the five stages of collagen fibre formation?
-precursor α chain -procollagen (triple helix with loose ends) -collagen molecule -collagen fibril -collagen fibre
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what are globular proteins?
spherical, complex tertiary and sometimes quaternary
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how does their large size affect their behaviour in water?
form a colloid instead of dissolving
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what important things do globular proteins do? (2)
-hold molecules in position in cytoplasm -important in immune system (form antibodies)
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what type of protein is haemoglobin?
globular and conjugated
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what is a conjugated protein?
a protein associated with a prosthetic group; e.g. for haemoglobin it is an iron-containing haem group
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how many amino acids is haemoglobin made up of?
574 amino acids
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what type of bonds hold haemoglobin together?
disulfide bonds
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what is the significance of the haem prosthetic group?
iron enables haemoglobin to bind and release oxygen molecules, arrangment of polypeptides around haem group determine how easily oxygen can bind or release
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what is another example of a conjugated protein?
chlorophyll, with prosthetic group of magnesium (needed to produce chlorophyll)
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what is a glycoprotein?
protein with carbohydrate prosthetic group
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why are glycoproteins useful?
carbohydrate part of molecule helps them to hold onto a lot of water and makes it harder for proteases to break them down
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what are some examples of glycoproteins?
mucus and synovial fluid (lubricants); water-holding properties allow them to be viscous, reducing friction, how mucus stops protein walls in stomach from being digested
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what are lipoproteins?
proteins with lipid prosthetic group
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why are lipoproteins useful?
important in transport of cholesterol in blood, lipid part allows it to combine with lipid cholesterol
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what are the two main types of lipoproteins in the blood?
LDLs (low density lipoproteins) (22nm in diameter) and HDLs (high density lipoproteins) (8-11nm in diameter)
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why are HDLs more dense?
contain more protein; proteins more compact than lipids
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what are the two tests for protein?
(1) add 5% potassium or sodium hydroxide and 1% copper sulfate (2) biuret reagent (two chemicals already mixed); for both, results should be colour change from blue to purple
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Other cards in this set

Card 2

Front

what does protein form in terms of appearance? (6)

Back

skin, hair, nails, horns, claws, feathers

Card 3

Front

what does protein form inside the body? (3)

Back

Preview of the front of card 3

Card 4

Front

what do they allow to happen? (3)

Back

Preview of the front of card 4

Card 5

Front

how do they differ from lipids and carbohydrates?

Back

Preview of the front of card 5
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