2.7 Proteins

Question 1

What is a protein?

Answer 1

a polymer composed of amino acid monomers

Question 2

What is an amino acid?

Answer 2

an organic molecule composed of a central carbon atom bonded to a hydrogen atom and 3 functional groups

• amino group (–NH2)
• acidic group (–COOH)
• ‘R’ group

Question 3

What does the ‘R’ group of an amino acid determine?

Answer 3

the uniqueness of each amino acid

Question 4

What is the ‘R’ group of an amino acid?

Answer 4

varies from having a single carbon to being a complicated ring structure

Question 5

What is keratin?

Answer 5

structural protein that makes up hair and nails

Question 6

What is collagen?

Answer 6

structural protein that lends support to ligaments, tendons, and skins

Question 7

What are enzymes?

Answer 7

proteins that speed up chemical reactions and are necessary contributors to the chemical workings of the cell, and the body

Question 8

What are hormones?

Answer 8

proteins that are messengers that influence cellular metabolism

Question 9

What are actin and myosin?

Answer 9

proteins that account for the movement of cells and the ability of our muscles to contract

Question 10

What is hemoglobin?

Answer 10

a complex protein in our blood that transports oxygen

Question 11

What are antibodies?

Answer 11

proteins in blood and other body fluids that combine with foreign substances, preventing them from destroying cells and upsetting homeostasis

Question 12

What are the functions of proteins in the plasma membrane of cells?

Answer 12

• some form channels that allow substances to enter and exit cells
• some are carriers that transport molecules into and out of the cell
• some are enzymes

Question 13

What does the synthesis reaction between two amino acids result in?

Answer 13

a dipeptide and a molecule of water

Question 14

What is a polypeptide?

Answer 14

a chain of amino acids that are joined to one another by a peptide bond

Question 15

What is a peptide bond?

Answer 15

a type of bond that joins amino acids together in a polypeptide

Question 16

Why do the atoms associated with a peptide bond unevenly?

Answer 16

because oxygen is more electronegative than nitrogen

• the hydrogen attached to the nitrogen has a slightly positive charge
• oxygen has a slightly negative charge

Question 17

What does the polarity of the peptide bond mean?

Answer 17

hydrogen bonding is possible between the C=O of one amino acid and the N-H of another amino acid in a polypeptide

Question 18

What does hydrogen bonding influence in proteins?

Answer 18

structure/shape of a protein

Question 19

What are the 4 levels of protein organization?

Answer 19

primary
secondary
tertiary
quaternary

Question 20

What is the primary structure?

Answer 20

the linear sequence of the amino acids joined by peptide bonds

Question 21

How do polypeptides differ from one another?

Answer 21

a polypeptide chain is made from 20 different amino acids, each with its own sequence of amino acids and its own sequence of ‘R’ groups

Question 22

How does the secondary structure come about?

Answer 22

when the polypeptide takes on a certain orientation in space

Question 23

What are the 2 possible shapes of the secondary structure?

Answer 23

alpha helix

beta pleated sheet

Question 24

What causes the polypeptide to form a alpha helix or beta pleated sheet?

Answer 24

hydrogen bonding between amino acids

Question 25

What results in an alpha helix?

Answer 25

a coiling of the chain

Question 26

What results in a beta pleated sheet?

Answer 26

a folding of the chain

Question 27

What is the tertiary structure?

Answer 27

the final 3D shape of a protein

Question 28

What shape do myosin molecules in muscles have?

Answer 28

a rod shape ending in globular heads

Question 29

What shape do enzymes have in the tertiary structure?

Answer 29

the polypeptide bends and twists in different ways

Question 30

Where are hydrophobic and hydrophilic portions in the tertiary structure?

Answer 30

hydrophobic: packed mostly on the inside hydrophilic: on the outside where they can make contact with water

Question 31

How is the tertiary shape of a polypeptide maintained?

Answer 31

by various types of bonding among the 'R' groups: covalent, ionic, and hydrogen bonding all occur

Question 32

What is a common form of covalent bonding between 'R' groups?

Answer 32

a disulfide (S-S) linkage between 2 cysteine amino acids

Question 33

How do proteins differ from one another?

Answer 33

- the number of polypeptides (each with its own primary, secondary, and tertiary structure) - length - sequence - structure

Question 34

What gives the tertiary structure a characteristic globular shape?

Answer 34

the polypeptide folds and twists due in part to covalent bonding between 'R' groups

Question 35

What is the quaternary structure?

Answer 35

occurs when 2 or more polypeptides join to form a single protein in proteins with multiple polypeptide chains, these separate polypeptides are arranged to give such proteins a fourth level of structure ie. hemoglobin and most enzymes

Question 36

Why is the final shape of a protein very important to its function?

Answer 36

- enzymes cannot function unless they have their normal shape - ONCE A PROTEIN LOSES ITS NORMAL SHAPE, IT IS NO LONGER ABLE TO FUNCTION NORMALLY

Question 37

What does 'denatured' mean?

Answer 37

describes a protein that has had an irreversible change in its shape due to exposure to extremes in heat and pH

Question 38

Give examples of denaturation?

Answer 38

- adding acid to milk causes curdling | - heating causes egg white (contains a protein called albumin) to coagulate

Question 39

Why does denaturation occur?

Answer 39

becasue the normal bonding between the 'R' groups has been disturbed

Question 40

What are prions?

Answer 40

structures formed by the alteration in protein organization and is related to the development of Alzheimer's diease and Creutzfeldt-Jakob disease (human 'mad cow' disease)

Question 41

What is the 'R' group of the amino acid Alanine?

Answer 41

a single carbon CH3

Question 42

What is the 'R' group of the amino acid Valine?

Answer 42

a branches carbon chain CH / \ H3C CH3

Question 43

What is the 'R' group of the amino acid Cysteine?

Answer 43

contains sulfur CH2 | SH

Question 44

What is the 'R' group of the amino acid Phenylalanine?

Answer 44

a ring structure CH2 | [hexagon]

Question 45

What are waxes?

Answer 45

long chain fatty acid attached to an alcohol, solid at room temperature

Question 46

What do waxes do?

Answer 46

protect from water (plants, ears) and energy storage in plankton

Question 47

What test do you use to detect the presence of protein? What colours does it change to and from?

Answer 47

Biuret's solution blue to violet