1.4.1 General properties of proteins Flashcards
Are amino acids soluble or insoluble in water?
Soluble
What do amino acids contain?
- An amino group (NH2)
- A carboxyl group (COOH)
- An R group
What do R groups do?
- They affect the way the amino acid groups bond to each other.
- They affect the 3D shape of a protein.
Definition of the primary structure?
The order and sequence of amino acids, held together by peptide bonds.
What will the primary structure determine?
How the polypeptide chain will later fold, and therefore the 3D shape.
What is the secondary structure formed as a result of?
The hydrogen bonds between amino acids (R groups).
What can the secondary structure of a protein be?
Alpha helix or beta pleated sheet.
Why will different R groups form more hydrogen bonds than others?
As they will contain more hydrogen.
What is the structure of an alpha helix?
A tight and twisted strand.
What is the structure of a beta pleated sheet?
- Zig-zag chains.
- 2 parts of the polypeptide chains are parallel to each other - with hydrogen bonds forming between them.
How does the tertiary structure of a protein form?
- By the irregular folding of the secondary structure.
- The folding results from the formation of the different bonds between the amino acids (R groups).
What are the 4 main types of bonds that form in the tertiary structure?
- Hydrogen bonds.
- Disulphide bonds.
- Ionic bonds.
- Hydrophobic and hydrophilic interactions.
Hydrogen bonds in the tertiary structure?
- Weakest bond ON ITS OWN.
- Most common bond -> formed between a wide variety of R groups.
- When there are many H bonds = strong overall bond.
- Formed between strongly polar R groups.
Disulphide bonds in the tertiary structure?
- Disulphide bridges can only form between R groups that contain sulphur.
Ionic bonds in the tertiary structure?
- The electrostatic interaction between POSITIVE amino groups and NEGATIVE carboxyl groups.
- Less common.
- Stronger than individual hydrogen bonds.
Hydrophobic and hydrophilic interactions in the tertiary structure?
- Hydrophobic R groups point inwards, and hydrophilic R groups point outwards in globular proteins.
What does the tertiary structure determine?
- The shape of the active site of enzymes.
- The function of proteins.
What is the quaternary structure of proteins?
The structure resulting from aggregation of several polypeptide chains.
What are conjugated proteins?
Proteins that derive part of their function from prosthetic groups.
What is a prosthetic group?
A non-protein group.
Give 2 examples of conjugated proteins?
Haemoglobin and collagen.
Condensation reactions of proteins?
- Join together 2 amino acids.
- A molecule of water is lost.
- A peptide bond is formed.
Structure of haemoglobin?
- 2 alpha helices and 2 beta-pleated chains.
- Held in position around 4 iron groups.
4 polypeptide chains
with 1 haem group
Where does oxygen attach to in haemoglobin?
The iron in the haem group.
What is haem?
A pigment containing iron.
Is haemoglobin soluble or insoluble in water?
Soluble
Where is collagen present?
In bones and tendons.
Structure of collagen?
- 3 polypeptide chains.
- Coiled around each other.
- With hydrogen bonds between the chains.
Is collagen a strong molecule?
Yes.
What are the 2 types of protein structures?
Fibrous and globular.
Shape of fibrous proteins?
- Parallel chains that cross at regular intervals.
Shape of globular proteins?
Roughly circular.
Amino acid sequencing in fibrous proteins?
Repetitive.
Amino acid sequencing in globular proteins?
Irregular.
Are fibrous proteins generally soluble or insoluble in water?
Insoluble.
Are globular proteins generally soluble or insoluble in water?
Soluble.
Describe how the structure of a protein depends on the amino acids it contains.
- Primary structure is determined by the order and sequence of amino acids.
- Secondary structure is formed by hydrogen bonding between amino acids.
- Tertiary structure is formed by interactions between R groups.
- Which creates the shape of active sites in enzymes.
- Quaternary structure contains more than 2 polypeptide chains.
Describe a biochemical test to confirm the presence of protein in a solution.
- Add biuret reagent.
- Positive result = turns purple.
from blue
What is a dipeptide?
A dipeptide consists of two amino acids joined by a peptide bond.
condensation of
what is a polypeptide
formed by the condensation of many AA
Describe two other ways in which all dipeptides are similar and one way in which they might differ.
S = Both contain an amine group.
S = Both contain a carboxyl group.
D = Different R groups.
Describe how a peptide bond is formed between two amino acids to form a dipeptide.
- Condensation reaction.
- Between amino and carboxyl group.
Describe how the secondary structure of a polypeptide is produced by bonds between amino acids.
- Hydrogen bonds form.
- Between NH group and C=O group.
- Forming either an alpha helix or a beta-pleated sheet.
Two proteins have the same number and type of amino acids but different tertiary structures. Explain why.
- Different sequence of amino acids.
- Different primary structure.
- Forms ionic, hydrogen, disulfide bonds in different places.
Aspartic acid and pralinee are both amino acids. Describe how two amino acids differ from one another.
different R groups
At what level of protein structure do hydrophobic interaction occurs?
Tertiary, Quaternary
Describe how a peptide bond is formed between 2 amino acids to form a dipeptide.
amino group and carboxylic group
Condensation reaction
Water removed
Describe how A quaternary protein is formed from its monomers
Amino acid joined by peptide bonds
- condensation reactions
- secondary structure formed by hydrogen bonding
- teritary structure is formed by interactions between R groups
- quaternary strcutre contains more than 1 polypeptide
- Quaternary strcutre is formed by interactions/ bonds between polypeptides
describe how Monomers join to form the primary structure of protein
1-Condensation reaction between 2 AA
2- creating specific Sequence of AA
3- Joined by peptide bonds
Describe how the structure of a protein depends on the amino acids it contains.
- Structure is determined by position of amino acid/
- Primary structure is sequence of amino acids;
- Secondary structure formed by hydrogen bonding
- Tertiary structure formed by interactions between R groups
- Creates active site in enzymes
Describe the structure of proteins.
- Polymer of amino acids;
- Joined by peptide bonds;
- Formed by condensation;
- Primary structure is order of amino acids;
- Secondary structure is folding of polypeptide chain due to hydrogen bonding;
Accept alpha helix / pleated sheet - Tertiary structure is 3-D folding due to hydrogen bonding and ionic / disulfide bonds;
- Quaternary structure is two or more polypeptide chains.
Different r group
different bonds form
different tertiary structure
Explain the tertiary structure of proteins and the forces involved in its formation + def
Folding of polypeptide into specific complex shape
due to IMFs between R group
e.g. Hydrogen bonds, ionic bonds, disulfide bridge and London forces
Genes - how does it code for production of a polypeptide:
1- Triplet
2- Base/ nucleotide sequence
3- determines order/ Sequences of AA
4- Primary structure in polypeptide determined
Give an example of a globular and a fibrous protein.
Globular- haemoglobin
Fibrous - collagen
How do amino acids provide indirect evidence for evolution?
The same 20 amino acids occur in all living organisms.
How is the presence of proteins tested using buret test, and what constitutes a positive result (Shows what??)
add copper sulphate and sodium hydroxide to a solution
+ve - blue - purple
shows presence of peptide bond
The secondary structure of a polypeptide is produced by bonds between amino acids. Describe how
hydrogen bonds
Between amino group and carboxylic group
Forming alpha helix or beta pleated sheets
two proteins have the same number and type of amino acids but different tertiary structures. Explain why
different primary sequence of AA
R group bond form in different places
Form ionic/ hydrogen/ disulphide bonds in different places
What elements do all proteins/amino acids contain?
carbon
hydrogen
oxygen
nitrogen
what is the primary structure of a protein and what role does it play in protein shape?
refers to sequence of amino acids in a protein
joined by peptide bonds
controls the overall protein shape and function
what is the significance of quaternary structure in proteins?
holds together multiple polypeptide chains
and other molecules necessary for protein function
therefore contributing to the overall structure and function of proteins
what type of bond is formed in condensation reaction to create a polypeptide
peptide bond
between amine group of one AA and carboxyl group
releasing water
