2.4 Proteins

Question 1

What are all protein polymer constructed from? What are the building blocks of proteins?

Answer 1

From the same set of 20 amino acids

Amino acids are the building blocks of proteins

Question 2

What are the monomers of proteins called? What bond is formed between amino acids?

Answer 2

Amino acids, also called peptide (or monopeptide)

Peptide bonds are formed between amino acids to make a chain called polypeptides

Question 3

What does the general structure of an amino acid have? What determines the reactivity of the amino acid?

Answer 3

An amino group, hydrogen, a carboxyl group, and a side chain.
The side chain is the most important in determining reactivity of the amino acid

Question 4

What is the order in which the different amino acids are linked together controlled by?

Answer 4

Genes on the chromosome

Question 5

What are essential amino acids?

Answer 5

Amino acids that must be obtained from our diet because we can’t manufacture them in our bodies

Question 6

How is a polypeptide chain formed? What is the process called? How functional is a polypeptide chain by itself?

Answer 6

• Formed when amino acids are linked together by peptide bonds to form long chains.
• The process of joining amino acids is called condensation.
• A polypeptide chain may be functional by itself, or may need to be joined to other polypeptide chains to become functional.

Question 7

What key role do proteins play in the body? What are they involved in?

Answer 7

• enzyme reactions
• oxidation – reductions
• structure
• Storage
• transport
• cell signaling
• defense

Question 8

What determines the confirmation of a protein? Is the function affected? What are the four levels of structure?

Answer 8

• The R groups of each amino acid reacts and interact with each other. This interaction determine the final conformation of the protein.
• If the shape is altered then the protein may no longer be able to perform its biological role
• primary, secondary, tertiary, quaternary

Question 9

What is it called when the bonds or interactions of the dimesional structure of proteins are broken? How can they we broken? Easy?

Answer 9

These bonds or interactions are weak and can’t be broken and disrupted fairly easily. When there is a change in confirmation of the proteins this is known as denaturation. It can be temporary or permanent. Two factors that come to nature proteins are heat and pH

Question 10

How does heat the nature proteins?

Answer 10

Heat can denatured proteins because it causes vibrations in the molecule that breaks the bond.
Proteins vary in their tolerance of heat and can cause temporary or permanent changes.

Question 11

How does PH cause proteins to denature?

Answer 11

Causes changes in the charges on R groups which breaks the bonds or causes new bonds to form. This will alter the structure of the protein

Question 12

What is the primary structure of proteins?

Answer 12

The amino sequence. Hundreds of amino acids linked together to form polypeptide chains.

Question 13

What is the secondary structure of proteins? What are two common types? What causes the secondary structure?

Answer 13

• Is the shape of the polypeptide chain.
• alpha-helix coil and beta-pleated sheets.
• Most proteins contain a mixture of the two secondary structures but the levels of each vary.
• It is a result of hydrogen bonds interaction between neighboring CO and NH groups of the polypeptide backbone.

Question 14

What is the tertiary structure of proteins? What causes it? What interactions may be involved?

Answer 14

• Is the way in which it is folded
• they fall because of interactions between the R group on the amono acids.
• disulfide bonding (reactions between two cysteine amino acids)
• weak bonding (ionic and hydrogen)
• hydrophobic interactions

Question 15

What is the quaternary structure of proteins? Why?

Answer 15

Some proteins contain more than one polypeptide chain. It is the aggregation of subunits.

• The polypeptide chains, or subunits, aggregate together to become a functional unit
• The aggregation of subunits is called a quaternary structure of a protein

Question 16

What does protein denaturation refer to? What are some examples of irreversible and reversible denaturation in everyday circumstances?

Answer 16

Proteins denaturation refers to the loss of a proteins 3 dimensional structure.
Occurs when the bonds responsible for maintaining protein structure are altered, usually results in loss of function, it is often irreversible.
e.g. cooking food denatures proteins and makes it easier to digest, alcohol disinfect by denaturing bacterial and viral proteins.
e.g. waving hair. The keratin protein in hair is denature using a reducing agent, then set, and finally glued back into a disulfide bridges by an oxidizing agent

Question 17

What causes proteins denaturation? (4)

Answer 17

• strong acids and alkalis
  These disrupt ionic bonds and resulting coagulation of the protein. Long exposure can also break down the primary structure of the protein
• heavy metals
  This may disrupt ionic bonds and form strong bonds with the carboxyl groups of the R groups and reduce the protein charge. This results in protein precipitation.
• heat and radiation
  These cause disruption of the bonds in the protein through increased energy provided to atoms
• detergent and solvents
  This form bonds with the non-polar groups in a protein, thereby disrupting hydrogen bonding

Question 18

How to categorize proteins? (2)

Answer 18

Proteins can be categorized according to the tertiary structure

• globular proteins
• Fibrous proteins

Question 19

What are globular proteins? What are their properties (3)? What are some functions? (4)

Answer 19

• globular proteins are very diverse in the structure. They can comprise as a single chains or comprise several chains, as occurs in hemoglobin and insulin.
• easily solvable, tertiary structure is critical to function, polypeptide chains are folded in a spherical shape
  Functions: catalytic (enzymes), regulatory (hormones), transport (hemoglobin), protective (antibodies?)

Question 20

What are fibrous proteins? What are the properties (3)? Where can they be found? Functions (2)?

Answer 20

• they form long shapes, and are only found in animals
• water insoluble, very tough physically; they may be supple or stretchy, parallel polypeptide chains in long fibres or sheets
• structural role in cells and organisms e.g. collagen in connective tissue, bones, tendons
• contractile e.g. myosin, actin

Question 21

How are proteins classified? What are some? (6)

Answer 21

Proteins can be classified according to their functional role in an organism

• structural: forming a structural components of tissues and organs
• regulatory: Cellular function (hormones, cell signalling)
• contractile: show me the contractile elements in muscle
• immunological: functioning to combat invading microbes
• transport: acting as carrier molecules
• catalytic: catalyzing metabolic reactions (enzymes)

Question 22

Why are proteins modified? Where are they modified? What does protein modification involve the additional of?

Answer 22

• are modified to perform specific roles
• proteins are produced by ribosomes, and can be modified at the RER or the golgi apparatus
• involves the addition of carbohydrates to form glycoprotein, or the addition of fatty acids to form lipoproteins

Question 23

What are glycoproteins? What are the roles?

Answer 23

• Proteins with carbohydrate groups covalently linked to them
• the carbohydrate groups help position or orientate glycoproteins in membranes. The carbohydrate groups prevent them from rotating in the membrane.
• may be important to intercellular recognition

Question 24

What are the basic types and functions of proteins? (8)

Answer 24

1) structural proteins - provide support
2) Storage proteins - developing embryo, source for baby animals, store proteins for plants
3) transport proteins - in body and across a membrane
4) hormonal proteins - coordination of an organisms activities
5) receptor proteins - response of cell to chemical stimuli
6) contractile proteins - movement of muscles
7) defensive proteins - protection against disease - antibodies
8) somatic proteins - selective acceleration of chemical reactions

Question 25

What is Rubisco and its function as a protein?

Answer 25

RuBisCO is the enzyme with an active site that catalyses the photosynthesis reaction that fixes carbon dioxide from the atmosphere, providing all the carbon needed by living organisms to make sugars and other carbon compounds

Question 26

What is insulin and its function as a protein?

Answer 26

Insulin is a hormone that is carried dissolved in the blood and bind specifically and reversibly to insulin receptors in the membranes of body cells, causing the cells to absorb glucose and lower the blood glucose concentration

Question 27

What is immunoglobulin and its function as a protein?

Answer 27

Immunoglobulins are antibodies that bind to antigens and pathogens. The immune system can produce a huge range of immunoglobulins, each with a different type of binding site, a lot of specific immunity against many different diseases

Question 28

What is rhodopsin and its function as a protein?

Answer 28

Rhodopsin is the pigment that makes the rod cells of the retina light sensitive. It has a non-amino acid part called retinal that absorbs a photon of light and when this happens the rod cell sends a nerve impulses to the brain

Question 29

What does collagen and it’s function as a protein?

Answer 29

Collagen is a structural protein. It has 3 polypeptides wound together to form a rope-like confirmation and it’s used in skin to prevent tearing, and bones to prevent fractures and tendons and ligaments to give tensile strength

Question 30

What is spider silk and its function as a protein?

Answer 30

Spider silk is a structural protein that is used to make webs for catching free and lifelines on with spiders suspend them selves. It has very high tensile strength and become stronger when it is stretched, so resisting breakage

Question 31

All the function of proteins

Answer 31