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MY BIOLOGY > Proteins and Enzymes > Flashcards

Proteins and Enzymes Flashcards

1
Q

What is an enzyme?

A

Globular proteins which reduce the activation energy of a chemical reaction by binding directly to one or more substrates

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2
Q

What do we mean by a catalyst?

A

A biological catalyst is something that speeds up a chemical reaction by reducing activation energy without being used up.

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3
Q

What is a globular protein?

A

A compact globe with hydrophobic bits on the inside and hydrophilic bits on the outside - therefore is soluble
They have a unique tertiary structure giving them a specific active site.

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4
Q

What is the general structure of an amino acid?

A

Amino group on the left, CH and a variable group in the middle, carboxylic acid group on the right hand side.

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5
Q

How are amino acids joined together?

A

Condensation reaction: a peptide (covalent) bond is formed and a water molecule is produced.

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6
Q

How is a dipeptide broken?

A

A water molecule is used to break the peptide bond in a hydrolysis reaction

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7
Q

What is a chain of amino acids called?

A

A polypeptide

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8
Q

What are polypeptides and proteins synthesised on?

A

The ribosomes on the rough endoplasmic reticulum

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9
Q

What is the primary structure of proteins?

A

The order of the amino acids

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10
Q

What is the primary structure of proteins held together by?

A

Peptide bonds

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11
Q

What is the secondary structure of a protein and what are the names of the two main structures?

A

Areas of initial folding
Two mains: alpha helices and beta pleated sheet

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12
Q

What holds the secondary structure of protein together?

A

Hydrogen bonds

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13
Q

What is the tertiary structure of a protein?

A

The tertiary structure is the 3D shape which involves interactions of the R groups and 4 types of bond/interaction

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14
Q

Name and explain the 4 types of bonds involved in tertiary structure of a protein?

A

1) Hydrogen bonds: when slightly positively charged H and slightly negatively charged O come into close contact hydrogen bonds form. Very weak.
2) Ionic bonds: some R groups are charged. Where oppositely charged groups come into close contact an ionic bond forms. Not particularly strong.
3) Disulfide bonds/ bridges: Cysteine (a type of amino acid) contains sulfur. When two cysteines are close, double covalent bonds form. These are very strong and difficult to break.
4) Hydrophobic and hydrophilic interactions: hydrophobic amino acids will be most stable where there is no water present. Hydrophilic amino acids will be found on outside and hydrophobic on inside (of enzyme)

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15
Q

What is the quaternary structure of a protein?

A

When two or more polypeptides join together or there is a prosthetic group (a non protein group)

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16
Q

What is a conjugated protein?

A

A globular protein with a prosthetic group

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17
Q

State the functions of globular proteins.

A

Globular proteins can act as enzymes, hormones and haemoglobin
Enzyme - Amylase
Hormone - insulin

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18
Q

What makes globular proteins soluble?

A

The hydrophilic amino acids are on the outside and the hydrophobic amino acids are on the inside.

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19
Q

Describe the structure of haemoglobin?

A

It has 4 polypeptide chain subunits (2 alpha 2 beta)
Embedded within 4 subunits there are 4 haem groups (prosthetic groups) containing Fe2+
It is a conjugated protein which is soluble

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20
Q

Describe the structure of Amylase.

A

Globular protein
Soluble
Single chain of amino acids
Secondary structure has both alpha helix and beta pleated sheets
Only works if the ion/ cofactor Cl- is bound to it

21
Q

Describe the structure of insulin.

A

Globular protein
Soluble
Two amino acid chains joined by disulphide bonds

22
Q

Describe the features of fibrous proteins.

A

Only has secondary structure (no tertiary or quaternary)
Long parallel chains
Insoluble
No prosthetic group
Usually form fibre structures

23
Q

Name 3 fibrous proteins.

A

Collagen
Keratin
Elastin

24
Q

What are the functions of collagen?

A

Prevents the walls of arteries from bursting under high pressure (strong)
Tendons (connect muscle to bone) are made of collagen. Form a strong connection that permits muscles to pull the bone creating movement.
Spongy layer in the middle of bones consists of collagen.

25
Q

Give an example of an enzyme that catalyses intracellular reactions.

A

Catalase: catalyses decomposition of hydrogen peroxide into water and oxygen

26
Q

Give 2 examples of enzymes that catalyse extracellular reactions.

A

Amylase: carbohydrase catalyses digestion of starch to maltose in saliva/ small intestine lumen
Trypsin: pancreatic endopeptidase catalyses hydrolysis of peptide bonds in small intestine lumen

27
Q

Explain the induced fit model of enzyme action.

A

The substrate isn’t exactly complimentary to the active site. The active site has to change shape slightly to fit the shape of the substrate in order to form an enzyme substrate complex

28
Q

Explain the lock and key model of enzyme action.

A

This model suggests that the active site has a rigid shape determined by the tertiary structure so is only complementary to 1 substrate.

29
Q

Name 5 factors that affect the rate of enzyme controlled reactions.

A

Enzyme concentration
Substrate concentration
Concentration of inhibitors
pH
Temperature

30
Q

How does substrate concentration affect rate of reaction?

A

As we increase substrate molecules there are more collisions so the rate of reaction increases. This only continues until all the enzymes active sites are full. After this point substrate concentration will have no effect on the rate of reaction.

31
Q

What are the biological roles of proteins?

A

Structural: muscle, skin, hair
Catalytic: enzymes
Cell signalling: hormones and receptors
Immunological: antibodies

32
Q

How many different variable groups (r groups) can there be on an amino acid?

A

20

33
Q

When does a protein stop working properly?

A

When the bonds that maintain its shape are broken and the protein has denatured.

34
Q

When denatured what happens to fibrous and globular proteins?

A

Fibrous proteins lose their structural strength and globular proteins become insoluble and inactive

35
Q

What are the functions of keratin?

A

Keratin is the main component of hard structures such as hair nails claws etc

36
Q

What is the function of elastin?

A

It is a major protein component of tissues that require elasticity such as arteries, ligaments etc

37
Q

Explain the effect of increasing enzyme concentration on rate of reaction.

A

More enzyme substrate complexes form so rate of reaction increases until the point where all of the substrate molecules are occupying active sites

38
Q

What is an inhibitor?

A

Any substance or molecule that slows down the rate of an enzyme controlled reaction by affecting the enzyme in some way

39
Q

What is a competitive inhibitor?

A

Competitive inhibitors have a similar shape to substrates and occupy the active site to form an enzyme inhibitor complex. This stops the substrate from fitting into the active site so it cannot catalyse the reaction.

40
Q

What are non competitive inhibitors?

A

Non - competitive inhibitors attach to an area away from the active site called the allosteric site. They distort the 3D tertiary structure which does change the enzymes active site and the substrate can no longer fit into active site.

41
Q

What is a cofactor?

A

A non protein substance needed for the enzyme to work

42
Q

What are coenzymes?

A

Small organic non proteins which temporarily bind to the active site and take part in the reaction.

43
Q

How can ions increase rate of reaction?

A

They can combine with the enzyme or substrate so that the enzyme substrate complex can form easier by changing charge distribution and sometimes shape.

44
Q

Give an example of an inorganic ion and where it is used.

A

In order for amylase to work it requires chloride ions

45
Q

Give an example of a prosthetic group.

A

Zinc is a prosthetic group for the enzyme carbonic anhydrase

46
Q

What is end product inhibition?

A

When there is a metabolic pathway (the product of one reaction is the substrate of another) the final product must not build up so it acts as an inhibitor to the first reaction to stop it from happening.

47
Q

How does temperature affect enzyme activity?

A

More kinetic energy means more vibrations which puts a strain on bonds
This can break the weaker bonds (hydrogen and ionic) and change the shape of the active site
As you heat an enzyme, more and more bonds are broken
Rate of reaction decreases until tertiary structure of enzyme unravels and enzyme denatures

48
Q

How does pH affect enzyme activity?

A

As H+ ions are positively charged they attract negatively charged molecules. Tertiary structure is held together by lots of H bonds and ionic bonds
H+ ions interfere with H bonds and ionic bonds
So if you increase the amount of H+ ions you can change the active site and if you increase the number or OH_ ions you can change the active site

MY BIOLOGY (11 decks)

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