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Biology- A level > Proteins > Flashcards

Flashcards in Proteins Deck (38):
1

What are proteins made from?

Long chains of amino acids

2

Functions of proteins

Structural components- e.g muscles
Enzymes,antibodies and some hormones
Found in membranes e.g they act as carriers and pores for active transport and facilitated diffusion.

3

How are protein adapted to their function as an enzyme?

They can adapt to specific shapes

4

Structure of amino acids

Amine group (left)
Hydrogen group (top)
R group (bottom)
Carboxyl group (right)

5

How many types of amino acids are there?

There are 500 types of amino acids but only 20 of them are proteinogenic (found in protein)

6

What covalent bond is formed when a dipeptide is formed by condensation?

A peptide bond

7

Why is a polypeptide bond stiff and rigid?

The peptide bond has properties of a double bond which inhibits rotation. Even though it's depicted as a single bond, the bond is shorter than a typical C-N bond.

8

Primary structure of protein

The number and order of amino acids which are held by strong peptide bonds form a sequence.
As there 20 different amino acids, differences in the chain could alter the proteins shape and function.

9

Approximately how many amino acids are there in one Protein

Around 100
Therefore there are 20 to the power of 100 possible ways of ordering them.

10

For secondary structures what can the chain twist into

An a-helix (36 amino acids per 10 turns)
or a beta-pleated sheet (zig zag)

11

What bonds are many found in the secondary structure?

Hydrogen bonds

12

What bonds are found in the tertiary structure?

Hydrogen bonds
Ionic bonds
Disulfide links
Hydrophobic and hydrophilic interactions

13

What shape can be formed? (Tertiary structure)

Can form a supercoiled shapes (in fibrous protein) or a more spherical shape (globular proteins) which was held tightly by bonds

14

Describe the quaternary structure

Made up of multiple polypeptide chains arranged to form a complete protein which are help by bonds similar to the tertiary structure

15

Hydrogen bonds in tertiary structure

Forms between hydrogen atoms s+
And atom with s- charge
E.g OH-, COOH- and NH2-

16

Ionic bonds in tertiary structure

Can form between carboxyl- amine group
Ionises into NH+3 and COO-

17

Disulfide links in tertiary structure

Strong covalent bond
R group of the amino acid cysteine has a sulfide group
Bond between two R groups

18

Hydrophobic and hydrophilic interactions in the tertiary structure

Hydrophilic on the outside
Hydrophobic on the inside
Interaction causes twisting (determines shape)
Important because proteins are usually found surrounded by water in living organisms

19

Collagen

Mechanical strength
Found in:
Artery wall- prevents bursting from high pressure
Tendons- connected to bones, allows it to pull on bones
Bones (calcium phosphate makes it hard)
Cartilage
Connective tissue

20

Keratin

Rich in cysteine (lots of S-S bonds and H bonds)
Found in:
Hair
Nails
Claw
Feathers
Hooves

21

Elastin

Strong and extensible - due to cross linkage
Found in:
Skin (elastic)
Lungs
Blood vessels- stretches and recoils to maintain blood pressure

22

fibrous proteins

Regular repetitive sequences of amino acids
Usually insoluble in water
Usually structural

All features allow them to form fibres
E.g collagen,keratin, elastin

23

Globular proteins

Spherical shape
Hydrophilic on the outside
Hydrophobic on the inside
Makes the molecule soluble
Very specific shapes
E.g haemoglobin, insulin, pepsin

24

Haemoglobin

Made up of four polypeptide chains
Two alpha helix's and two beta-pleated sheet
Quaternary structure (very specific shape)
Outside each the chain there's a haem group (iron ion)

25

Role of haemoglobin?

The prosthetic group (iron ion) bonds to the oxygen and releases it when it gets to a cell.
It turns from purple-red >>>>> bright red

26

Insulin

Made up of two polypeptide chains
Quaternary structure
Both chains fold are folded together into a tertiary structure and they are joined together by disulfide links
Hydrophilic R group on the outside making it soluble in water

27

Role of insulin

Binds to the glycoprotein receptors on the outside of the muscle and fat cells to increase the consumption of glucose

28

Pepsin

Made of a single polypeptide (tertiary structure)

29

Test for carbohydrates

1. Add iodine solution ( potassium iodide)

Observation:
Yellow/brown>>>>black/blue

30

Reason for colour change

Iodine forms triiodide which slips into the middle of the amylose helix

31

Test for reducing sugars

All monosaccharide and some disaccharides

1.Heat with Benedictus solution/copper(II) sulphate (water bath 80 degrees)

Observation

Blue>>Green>>Yellow>>Orange-red (precipitate)

32

What do reducing sugars reduce?

The Cu2+ ions are reduced to Cu+ ions

33

Non-reducing sugars

1.First for reducing sugars to make sure there isn't any.
2. Use a separate sample and boil it with HCL
3.cool the solution and add sodium hydrogencarbonate to neutralise the solution
4. Should get a positive result for reducing sugars

34

Why is HCL used in the test for
non-reducing sugars?

The HCL hydrolyses the sucrose to glucose and fructose.

35

Test for lipids

1. Mix a sample with alcohol
2.Filter
3.pour solution into water in a clean test tube

Observation:
Cloudy white emulsion

36

What is emulsion?

The tiny droplets that come out of solution when mixed with water

37

Why is alcohol mixed with the sample when testing for lipids rather than water

It is insoluble in water

38

Test for proteins

1.Use the biuret test

Observation:

Light blue>>>>>>lilac