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BIOLOGY TOPIC 1.2 > PROTEINS > Flashcards

PROTEINS Flashcards

1
Q

What are amino acids?

A

They are the building blocks of proteins, consisting of an amino group (-NH₂) and a carboxyl group (-COOH) attached to a carbon atom and an R group that varies between amino acids.

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2
Q

What is a peptide bond?

A

The bond formed by condensation reactions between amino acids.

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3
Q

What is a dipeptide?

A

Two amino acids joined by a peptide bond.

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4
Q

What is a polypeptide?

A

A long chain of amino acids joined by peptide bonds.

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5
Q

What are fibrous proteins?

A

Proteins that have long, parallel polypeptide chains with occasional cross-linkages that form into fibres, but with little tertiary structure.

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6
Q

What is a disulfide bond?

A

A strong covalent bond formed as a result of an oxidation reaction between sulfur groups in cysteine or methionine molecules, which are close together in the structure of a polypeptide.

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7
Q

What are globular proteins?

A

Large proteins with complex tertiary and sometimes quaternary structures, folded into spherical (globular) shapes.

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8
Q

What is haemoglobin?

A

A large conjugated protein involved in transporting oxygen in blood, and gives the erythrocytes their red colour.

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9
Q

What is collagen?

A

A strong fibrous protein with a triple helix structure.

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10
Q

What is denaturation?

A

The loss of the 3D shape of a protein, e.g. as a result of temperature change or pH.

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11
Q

What is a prosthetic group?

A

The molecule that is incorporated in a conjugated protein.

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12
Q

What is a glycoprotein?

A

A protein with a carbohydrate prosthetic group.

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13
Q

What is a protease?

A

A protein-digesting enzyme.

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14
Q

What is a lipoprotein?

A

A protein with a lipid prosthetic group.

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15
Q

What do proteins do in the body? (5)

A
  • Form enzymes needed for metabolism & digestion.
  • Enable muscle fibres to contract.
  • Form antibodies that protect from disease.
  • Help clot blood.
  • Form hair, skin and nails.
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16
Q

What are proteins?

A

A group of macromolecules made up of many small monomer units called amino acids joined together by condensation reactions.

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17
Q

How many naturally occurring amino acids are there?

A

20.

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18
Q

What varies between amino acids and how does it affect the protein?

A

The R group, the structure of the R group affects the way the amino acid bonds with others in the protein, depending largely on whether the R group is polar or not.

19
Q

How do you form proteins from amino acids?

A
  • Amino acids join together by the reaction between the amino group of one amino acid, and the carboxyl group of another.
  • They join in a condensation where water is lost.
  • A peptide bond is formed when 2 amino acids join and a dipeptide is the result.
  • The R group is not involved.
  • More join together forming a polypeptide chain, when this folds or coils, it forms a protein.
20
Q

What other three bonds can form in amino acids depending on the R group?

A

Hydrogen, disulfide and ionic bonds.

21
Q

How do hydrogen bonds form in amino acids?

A
  • Tiny negative charges are present on the oxygen of the carboxyl groups & ting positive charges are present on the hydrogen atoms of the amino groups.
  • When they are close they attract, forming hydrogen bonds.
22
Q

Describe the strength of hydrogen bonds in amino acids.

A
  • Hydrogen bonds are weak, but they can potentially form between two amino acids positioned correctly, so there are lots of them holding the protein together firmly.
  • Hydrogen bonds break easily and reform if pH or temperature conditions change.
23
Q

How do disulfide bonds form?

A
  • When two cysteine molecules are close together in the structure of a polypeptide.
  • An oxidation reaction takes place between two sulfur containing groups, resulting in a strong covalent bond known as a disulfide bond.
24
Q

Describe the strength of disulfide bonds in amino acids.

A

-Disulfide bonds are much stronger than hydrogen bonds, but they occur much less often.

25
Q

How do you test for protein?

A

Either add 5% potassium or sodium hydroxide solution and 1 % copper sulfate solution, or Biuret reagent which is the two chemical ready mixed. When the reagent is added to a test solution, a purple colour indicated the presence of protein.

26
Q

How do ionic bonds form and what are the links called?

A

They form between some of the strongly positive and negative amino acid side chains found buried deep in the protein molecules. These links are known as salt bridges.

27
Q

Describe the strength of ionic bonds in amino acids.

A

They are strong bonds but not as common as other structural bonds.

28
Q

What protein is your hair made of?

A

Keratin.

29
Q

What does blow drying of straightening you hair do to it?

A

It breaks the hydrogen bonds and reforms them with the hair curling in a different way temporarily until the hydrogen bonds reform in their original places.

30
Q

What does perming do do your hair?

A

It breaks the disulfide bonds between the polypeptide chains and reforms them in a different place. The effect is permanent - until your hair is cut.

31
Q

What is the primary structure of a protein?

A

The linear sequence of amino acids that make up the polypeptide chain held together by peptide bonds.

32
Q

What is the secondary structure of a protein?

A

The secondary structure of a protein is the arrangement of the polypeptide chain into a regular, repeating structure, held together by hydrogen bonds. Such as an α-helix or β-pleated sheets.

33
Q

What is the tertiary structure of a protein?

A

The three-dimensional folding of the secondary structure.

34
Q

What is the quaternary structure?

A

The three-dimensional arrangement of more than one tertiary polypeptide.

35
Q

Explain how the structure of collagen results in its high strength.

A
  • The fibres have a high tensile strength.
  • The structure is made up of three polypeptide chains, which are each up to 1000 amino acids long.
  • The primary structure of these chains is repeating sequences of glycine w/ two other amino acids.
  • The 3 α-chains are arranged in a triple helix, held together by hydrogen bonds.
36
Q

Collagen fibres are found combined with…

A

Bone tissue.

37
Q

How does the size of globular proteins affect their behaviour in water?

A

Because the carboxyl & amino ends give them ionic properties you might expect them to dissolve in water and form a solution, but the molecules are so big they form a colloid.

38
Q

What roles do globular proteins play?

A
  • Important role in holding molecules in position in the cytoplasm.
  • Important in immune system, antibodies are globular proteins.
  • Globular proteins form enzymes and some hormones.
39
Q

Explain how the structure of haemoglobin is related to its function.

A
  • It is very large, made of 574 amino acids arranged in four polypeptide chains which are held together by disulfide bonds.
  • Each chain is arranged around an iron-containing haem group.
  • It is the iron that enables the haemoglobin to bind & release oxygen molecules, and its arrangement of polypeptide chains that determines how easily the oxygen binds/releases.
40
Q

What do lipoproteins do?

A
  • They are important in the transport of cholesterol in the blood.
  • The lipid part of the molecule enables it to combine w/ the lipid cholesterol.
41
Q

What are the two main forms of lipoproteins in your blood?

A

Low-density lipoproteins(LDLs)

High-density lipoproteins(HDLs)

42
Q

Why are HDLs more dense than LDLs?

A

HDLs contain more protein.

43
Q

What does the carbohydrate prosthetic group do in glycoproteins?

A

It helps them hold on to a lot of water and also makes it harder for protein-digesting enzymes (proteases) to break them down.

44
Q

Why are glycoproteins lubricants in the body?

A

Because they are slippery and viscous, which reduces friction.

BIOLOGY TOPIC 1.2 (4 decks)

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