Detailed notes protein

Question 1

What are proteins?

Answer 1

• Made up of the elements carbon, hydrogen, oxygen, nitrogen and sometimes sulpher.
• These elements combine amino acids
• Amino acids are carboxylic acids (COOH) that have a amino group (NH2) on the alpha carbon (C next to the carboxyl group) and a side chain (R group)

Question 2

Amino acids?

Answer 2

There are 22 known amino acids with 10 classified as essential and 12 non-essential. These amino acids combine to form complete and incomplete proteins.

Question 3

Complete proteins?

Answer 3

Means it contains all the essential amino acids.

Eg.

• Meat (myosin),
• Milk (casein, lactealbumen)
• Eggs
• Soy beans (glycinin)
• Nuts (excelsin)

Question 4

Incomplete proteins?

Answer 4

Lacking one or more essential amino acid

Eg.
Gelatin
Corn
Barley

Question 5

Protein function?

Answer 5

Provide the basis for the major structural components for animal tissue.

The way a protein functions is determined by its structure. There are at least three levels.

Question 6

The 3 protein structure levels?

Answer 6

Primary
Secondary
Tertiary

Question 7

Primary protein structure?

Answer 7

• Amino acids are liked by peptide linkages to form the basic chain of all protein molecules.
• Is a sequence of amino acids.
• The primary structure is resistant to chemical changes but enzymes are capable of splitting the chain into smaller units.

Question 8

Secondary structure?

Answer 8

This is the helical form. Is a coiled configuration found in many fibrous and globular food proteins.

The backbone chain is held into the coiled shape by H bonding.

Question 9

Tertiary Structure?

Answer 9

In some proteins the helically coiled backbone is tightly founded into a compact, spherical (globular) form due to interactions between the R-Group side chains of amino acids and may involve come weak bonding sources such as disulfide bridges, hydrophobic forces, salt bridges and H bonding.

Question 10

Different ways of classifying proteins?

Answer 10

Can be based in terms of:

• Neutral, basic or acidic R groups
• Shape: Aliphatic (straight) or Aromatic (e.g. benzene ring) and fibrous or globular
• Simple or conjugated
• In terms of functionality (what the amino acid can do)

Question 11

Classification based on Fiberous and globular?

Answer 11

Fibrous: rae proteins made up of elongated filamentous type chains and are usually insoluble in water.
Eg. Tough meat fibres (keratin)

Globular: Spherical or elliptical in shape and are usually soluble in water and fragile in nature.
Eg, most enzymes and caseins

Question 12

Classification based on Simple and conjugated?

Answer 12

Simple- are proteins that only produce amino adios on hydrolysis

Conjugated- produce amino acids and other organic or inorganic substances on hydrolysis.

Question 13

Classification based on Functionality?

Answer 13

• The amino acid can act as an acid because it contains a carboxylic acid group in the R group.
• The amino acid can act as a base because it contains an amine group in the R group.
• The amino acid can form H bonds because it has a hydroxyl (OH) group in the R group
• The amino acid is non-polar because in contain CH groupie in the R group
• The amino group and form a disulfide (- s - s -) links because the contain a supplied (-SH) group in the R group (S- amino acids)

Question 14

What is the significance of the fact that the amino acids have different
functional groups as their R groups?

Answer 14

Different functions groups as R groups affect the final structure of the protein and the properties and functions of the protein.

The R group determines the amino acid

Question 15

What is a functional group?

Answer 15

a functional group means a group of atoms in a molecule that have characteristic chemical reactions regardless of the rest of the molecule

Question 16

Properties of amino acids?

Answer 16

• Ability to form a peptide
• Acid/base properties
• Buffering properties
• Isoelectric point

Question 17

Proteins ability to form a peptide bonds?

Answer 17

• Ability or adjacent molecule to undergo a condensation reaction between the amino and carboxyl groups to form a peptide linkage.

Question 18

Proteins acid/base properties

Answer 18

• The carboxyl group and amino group are capable of ionising.
• This means that at the physiological pH (around 7.4), the carboxyl group which is a stronger acid than the amino group and will be deprotonated while the amino group will be protonated as shown in the following form:

R-COOH R-COO + H
R-NH3 R-NH2 + H

Molecules having this property are called Zwitterion or dipolar iron

Question 19

Buffering properties of proteins?

Answer 19

• Because amino acids re dipolar ion, this means that in water, they can act as either an acid or a base
• Proteins in solution contain either a weak acid or base
• The addition of either hydrogen ions (HCL) or basic hydroxide ions (NaOH) can be absorbed by these systems without altering the pH of the resulting solutions.
• Molecules having this property are called amphoteric molecules -> meaning ability to carry with a positive or negative charge under certain condition.

Question 20

What is a amphoteric molecule?

Answer 20

Ability to carry a positive or negative charge.

Proteins can sometimes do this because of their buffering properties

Question 21

Proteins as buffers in solutions?

Answer 21

Amino acids are effective buffers in aqueous solution. This means the pH will not be shifted in an acid or base in added.

Question 22

What will happen when you ad 1 drop of acid to milk?

Answer 22

Milk has a pH of 6.8. If only one drop is added there will be no change in pH as the protein will act as a buffer

Question 23

Do you know what the pH of the human blood is? What do you think is one of the functions of the proteins in our blood?

Answer 23

The pH for human blood is 7.35-7.45 and important function is to act as a buffer and maintain pH os 7.4. If pH changes too much damage will occur or death.

Question 24

Protein isoelectric point detailed notes?

Answer 24

• Each amino acid has own pH
• These relative acidic strengths are defined by “association constant to pKa”
• If you continue to add acid, a point is reached where the amino acid becomes is electrically neutral.
• This is called Isoelectric point (pI)
• Property has been used to separate protein based on their charge by a process of electrophoresis.

Question 25

What is the isoelectric point?

Answer 25

if you continue to add acid to a protein a point is reached when eventually the amino acid or protein is electrically neutral or has no charge. This pH is called the isoelectric point of the protein and is indicated by the symbol pI

Question 26

Denaturation?

Answer 26

A rearrangement of molecules in a native protein

Question 27

Adding acid to milk?

Answer 27

• Adding lots of acid to milk will make it go lumpy
• The proteins that form those lumps are called casein proteins
• As the precipitated (went lumpy) after the addition of acid, they were clearly sensitive to acid (acid-sensitive)
• The precipitated protein is denatured
• The protein has coagulated (formed precipitates)
• If the lumpy milk produced is filtered so all lumps are removed we are left whey.
• Then heating this a skin will form on top called whey protein.
• Because the whey proteins formed a skin it means they are heat sensitive proteins

Question 28

Acid and heat sensitive proteins in milk?

Answer 28

Casins- acid sensitive

Whey ect. - Heat sensitive

Question 29

Enzyme and fruit discolouration?

Answer 29

Some fruits and veg will develop a brown colouration quickly when peeled or sliced? This process of call enzymic browning.

Question 30

This that need to be present for enzymic browning to occur?

Answer 30

• A particular substrate (Phenolic compound- not in lemon)
• The enzyme polyphenol oxidase
• Close to neutral pH
• Temp around 37 degrees
• Oxygen

MOST IMPORTANTLY!

The cell membranes need to be cut/damaged so they rupture and allow the enzyme and substrate to react with each other.

Question 31

Substrate?

Answer 31

A substrate is a substance upon which the enzyme acts on

Question 32

Enzymes and pH?

Answer 32

The pH can change the structure of an enzyme and there is a pH environment level at which they are most active

Question 33

Enzymes and Temp?

Answer 33

The optimum temp is around 35-40 degrees for most enzymes. At high temps enzymes (being proteins) are inactivated. AT low temps they work very slowly.