Proteins Flashcards
What are the monomeric units of proteins?
Amino acids
Where do we get amino acids from?
Our diet
Outline the journey an amino acid takes from food to protein in a cell
- food is ingested
- enzymes in the stomach/small intestine hydrolyse protein into amino acids
- the amino acids are absorbed by the gut wall into the blood
- the amino acids leave the blood in the tissue fluid and enter cells
- proteins are synthesised on the ribosomes
How many common amino acids are there?
20
Give 4 functions of proteins
- enzymes
- hormones
- antibodies
- structural proteins
What do the interactions of differing R-groups determine?
The folding of the protein
What type of reaction occurs to form a protein from 2 amino acids?
Condensation
What type of bond is formed from the synthesis of a protein?
Peptide
What is produced in the condensation reaction between two amino acids?
Water and dipeptide
What is the general formula of an amino acid?
Between which parts of the amino acid molecules does the condensation reaction between two amino acids occur?
The carboxyl group of one amino acid and the amine group of another amino acid
What is a chain of amino acids called?
A polypeptide
What is the end of a polypeptide with an amino group called?
The N-terminus
What is the end of the polypeptide with a carboxyl group called?
The C-terminus
What is the definition of primary structure of a protein?
The SEQUENCE of amino acids
What type of bonding holds the primary structure of a protein together?
Peptide
What shape is the primary structure of a protein?
Linear
What forms the secondary structure of a protein?
The folding of the primary structure
What type of bonds hold together the secondary structure of a protein?
Hydrogen bonds
In the secondary structure, what do hydrogen bonds form between?
Partially positive H and partially negative O
What are the two possible shapes of the secondary structure?
- alpha helix
- beta pleated sheet
What is the tertiary structure formed by?
The folding of the secondary structure
Why do proteins fold at the tertiary level of structure?
Due to the interactions between the R-groups
What are the 4 types of bond formed at the tertiary level of structure?
- ionic bonds
- hydrogen bonds
- disulfide bonds
- hydrophobic and hydrophilic interactions
What do ionic bonds form between?
Positively and negatively charged ions
What do hydrogen bonds form between?
Partially positive H and partially negative O
What do disulfide bridges form between?
Sulfur atoms contained within R-groups
Which amino acid contains sulfur?
Cysteine
What do hydrophobic and hydrophilic interactions form between?
Polar and non-polar R-groups
What kind of shape does the tertiary structure have?
3D
What forms the quaternary structure?
Formed by the interaction of more than one tertiary protein and/or with prosthetic groups
What type of bonds holds together the quaternary structure?
-ionic -hydrogen -disulfide -hydrophobic and hydrophilic interactions
What is a prosthetic group?
a non-protein component of a conjugated protein
Define simple proteins
Proteins without a prosthetic group
Give 3 characteristics of globular proteins
-compact -water soluble -roughly spherical
Why are globular proteins water soluble?
-TERTIARY structures are folded so that the hydrophobic R-groups are kept away from the aqueous environment -hydrophilic R-groups are on the outside
What are globular proteins used for?
-regulating many processes
Give examples of the processes globular proteins regulate
-muscle contraction -immunity -chemical processes
Give an example of a globular protein
Insulin
Why is it beneficial for insulin to be water-soluble?
-insulin is a hormone -hormones are transported in the blood so must be water soluble
What is the function of insulin?
Regulates blood glucose
Are conjugated proteins a type of globular protein?
Yes
What do conjugated proteins contain?
A non-protein prosthetic group
Give an example of 2 conjugated proteins
Haemoglobin Catalase
What is the function of haemoglobin?
Carries oxygen in the blood in erythrocytes
What is haemoglobin made up of?
2 alpha-helices 2 beta-pleated sheets
How many subunits make up haemoglobin?
4
What does each haem group contain?
Iron 2+ ion
What does each subunit of haemoglobin contain?
A haem group
How do haem groups allow erythrocytes to carry out their function?
Iron ions in haem groups can reversibly combine with an oxygen molecule
How many oxygen atoms can one haemoglobin molecule carry?
8- remember ATOMS not MOLECULES
Define globular protein
spherical, water-soluble proteins
Define fibrous protein
long, insoluble, structural proteins
What is the function of catalase?
Break down of hydrogen peroxide which otherwise is harmful to cells
What type of protein is catalase?
Conjugated
What type of prosthetic group does catalase contain?
Haem
How many haem groups does catalase contain?
4
Give 3 examples of fibrous proteins
Collagen Elastin Keratin
Where is Keratin found?
In hair, skin, and nails
How does the primary structure of repetitive amino acid sequences affect the properties of fibrous proteins?
-gives them organised structures -makes strong molecules that do not fold into complex 3D shapes
Which amino acid does keratin contain in a high proportion?
Cysteine
What does Cysteine contain in its R-group?
Sulfur
What type of bonding occurs a lot in keratin?
Disulfide bonds
How does a high proportion of disulfide affect the properties of keratin?
It makes it inflexible and strong
Where is elastin found?
In the walls of blood vessels and alveoli of lungs
What does elastin allow tissues to do?
Expand and return to size
Why is it beneficial for tissues to contain elastin?
It confers strength and elasticity
What makes up elastin?
Aggregates of tropoelastin
Where is collagen found?
In the skin, tendons, ligaments, and nervous system
Why does collagen contain glycine for every 3rd amino acid?
Glycine is the smallest amino acid and so they can pack together more tightly
What property does collagen have?
Flexibility
Define polypeptide
Chains of 3 or more amino acids
Define protein
one or more polypeptides arranged as a complex macromolecule
