1.6 Proteins

Question 1

What are amino acids

Answer 1

Basic monomer units which combine to make up a polymer called a polypeptide.

Question 1

What can polypeptides be combined to make

Answer 1

A protein

Question 2

How many amino acids occur naturally in protein

Answer 2

20 out of 100 amino acids

These 20 amino acids occur in all living organisms- which provides evidence for evolution

Question 3

Each amino acid has a central carbon atom which connects to four different chemical groups

What are they

Answer 3

. An amino group (-NH2)
Basic group that gives it its name

. Carboxyl group (-COOH)
Acidic group which makes it acidic

. Hydrogen atom (-H)

. R group
Which Is a variety of different chemical groups. Each amino acid has a different R group
. Amino acids only differ in their R groups

Question 4

What bond is formed between amino acid monomers to form a dipeptide

Answer 4

Peptide bond

Question 5

What type of reaction is it when a dipeptide is formed

Answer 5

. Condensation reaction: a molecule of water is removed from the reaction

Question 6

How is the water molecule made from amino acids bonding

What bond forms between them

Answer 6

Condensation reaction:

The OH from carboxyl group of one amino acid and a H from the amino group of another amino acid

A peptide bond forms between them

These make H2O

Question 7

How can the peptide bond be broken

Answer 7

Hydrolysis, adding a molecule of water , to give two constituent amino acids

Question 8

What is the primary stage of proteins

Answer 8

Polypeptides:

. Amino acid monomers joined together in polymerisation

. The sequence of amino acids in a polypeptide chain forms primary structure of any protein

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Question 9

Why are there many types of primary protein structure

Answer 9

. The 20 naturally occurring amino acids join in different sequences so there are loads of possible combinations

Question 9

What does the primary structure of a protein determine

Answer 9

. It ultimate shape and hence its function

. A change in a single amino acid in the primary sequence can change the shape of the protein stop it carrying out its function

Question 10

What is the secondary structure of proteins

Answer 10

. Linked amino acids that make up polypeptides possess both NH and -C=O groups.

These groups have opposite charges due to oxygen having - charge and H having + charge

. These groups form hydrogen bonds

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The shape can be an alpha helix or beta sheets, but both are formed by hydrogen bonds

Question 11

What do the hydrogen bonds on secondary structure of proteins cause

Answer 11

Cause long polypeptide chain to be twisted into a long 3D shape like the coil on an alpha helix

Question 12

What is the tertiary structure of proteins

Answer 12

The alpha helixes of secondary protein can be twisted and folded even more to give complex 3D structure of each protein

This structure is maintained by a number of different bonds. Where the bonds occur depend on the primary structure

Looks like a knot a bit

Question 13

What 3 types of bonds are found on tertiary structure

Answer 13

. Disulphide bridges: Fairly strong and not easily broken

. Ionic bonds: Formed between carboxyl and amino groups that aren’t involved in forming peptide bonds.
They’re weaker than disulphide bonds and are easily broken by changes in PH

.Hydrogen bonds: Numerous but easily broken

Question 14

What is the quaternary structure of proteins

Answer 14

Large proteins form complex molecules containing lots of individual polypeptide chains linked in various ways.

There can be non proteins (prosthetic groups) associated with the molecules also

Question 15

How do you test for proteins

Answer 15

Biuret test: Detects peptide bonds

. Place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temp

. Add a few drops of dilute copper sulfate solution, and mix gently

. Purple colouration indicates peptide bonds being present, and hence a protein

If no protein is present solution remains blue

Question 16

What function do fibrous proteins have

Give the example

Answer 16

. Eg collagen, have structural functions

Question 17

Structure of fibrous proteins

Answer 17

. Form long chains which run parallel to each other so cross bridges link them together.
This makes them very stable

Question 18

What is the primary structure of collagen

Answer 18

. Unbranched polypeptide chain

Question 19

Secondary structure of collagen

Answer 19

. Polypeptide chain is very tightly wound

The amino acid glycine is present as every 3rd amino acid helps tight packing

Question 20

Tertiary structure of collagen

Answer 20

. Chain is twisted into a second helix

Question 21

Quaternary structure of collagen

Answer 21

. Made up of 3 polypeptide chains wound together in the same way as individual fibres are wound together in a rope

Hydrogen bonds keep it together

Question 22

What are globular proteins

Answer 22

Eg enzymes and haemoglobin carry out metabolic functions

Question 23

Shape of globular proteins

Answer 23

Spherical, glob shape

Question 24

Solubility of globular proteins, why?

Answer 24

Soluble in water Because some amino acids have hydrophilic R groups that are attracted to water . They have hydrophilic amino acids on their surface, so they interact with water molecules The hydrophobic amino acids are in the centre of the protein, away from water

Question 25

Name the 4 types of body proteins

Answer 25

Structural proteins, enzymes, antibodies, hormones

Question 26

Describe the structure of antibodies

Answer 26

Globular proteins: Two pairs of polypeptide chains eg 2 long and 2 short

Question 27

What do channel proteins do How does its structure relate to its function

Answer 27

Its primary function is to transfer ions and water molecules through the membrane: Involved in substances entering and leaving the cell It has a hydrophilic and a hyrophobic side so one side attracts water nd the other repels water. This allows the protein to fold up and form a channel through the cell membrane where the water soluble molecules can pass through

Question 28

Where is collagen found

Answer 28

Tendons: which join muscles to bones