UNIT 1 - B 1.2 - Proteins Flashcards
What do cells use the 20 amino acids to synthesize?
Polypeptides or proteins
What does a gene do for a polypeptide?
it codes each polypeptide
What determines the identity of a polypeptide?
the sequence of amino acids
Why does the shape of a protein matter?
It determines the protein’s function
What may happen if the structure of a protein changes?
It may not be able to function as it should
What are two environmental factors that could change the shape of protein?
termperature and pH
How do proteins become an alternate shape with certain temperatures or pH levels?
Chemical bonds within the protein may be created or broken, changing its shape
What is the structure of an amino acid?
an amine functional group bonded to a central carbon which has H and R, and a carboxyl functional group on the other side of the central carbon
What is the formula of an amine functional group?
NH2
What is the formula for a carboxyl functional group?
COOH
Where are the double bond(s) in the structure of an amino acid?
There’s one bonding carbon and oxygen in the carboxyl functional group
What is the R in the amino acid structure?
1 of the 20 variable groups/side chain
What kind of reaction takes place to form a depeptide?
condensation reaction
Where does the condensation reaction occur to form a dipeptide?
Between the OH of the carboxyl group of one amino acid and the H of an amine group of another amino acid
What is the word equation for the condensation reaction between two amino acids?
amino acid 1 + amino acid 2 = dipeptide + water
What is a peptide bond?
The bond between the C and N combining two amino acids after a condensation reaction
What is a polypeptide?
A chain of multiple amino acids together by peptide bonds
How many of the 20 amino acids can our cells synthesize?
11
Where do the other 9 amino acids come from?
Our diet
What are essential amino acids?
The 9 amino acids that we can only get from our diet
What is a good source of essential amino acids?
meat
What are non-essential amino acids?
The 11 amino acids that our bodies synthesize
How are the huge variety of polypeptides possible?
DNA codes for the number and order of amino acids within polypeptides, there are 20 different amino acids, polypeptides can vary in length, some polypeptides are modified by cells after their initial synthesis, amino acids can be arranged in any order
What are some examples of common polypeptides?
haemoglobin (found in red blood cells), keratin (found in hair, nails, claws, hooves), lipase (digestive enzyme), collagen (found in connective tissue), histones (proteins found in nucleus), insulin (hormone that helps regulate blood sugar)
What does the precise 3D shape of proteins result from?
Intramolecular bonds between amino acids such as hydrogen bonds
What is denaturation?
When proteins lose their shape and function
What happens when a fluid environment such as cytoplasm or blood plasma is flooded with either Hydrogen ions or OH ions?
The extra charges can prevent normal hydrogen bonding and the protein will lose its normal 3D shape
What happens when protein molecules are placed into an environment that is at a higher temperature than their physiological optimum?
the increased molecular motion puts stress on the weak hydrogen bonds and they cannot stay in place under the stress, therefore the protein loses its 3D shape
What would be the main reason why denaturation would not be reversible?
If the underlying polypeptide chain was damaged
How many different “R” groups are there for amino acids?
20
What do amine and carboxyl groups do when in a neutral aqueous solution?
They ionize
Why do amine and carboxyl groups ionize when they are in a neutral aqueous solution?
Because the carboxyl group acts as an acid and donates a hydrogen ion while the amine group acts as a base and accepts a hydrogen ion
What is a result in carboxyl and amine groups ionizing?
The carboxyl group has a negative net charge and the amine group has a positive net charge
What is the division of amino acids into polar and non-polar categories based on?
The “R” group
Which amino acids are hydrophobic
Hydrophobic= non-polar
How many amino acids are non-polar?
9
What does it mean for the “R” group if the amino acid is non-polar?
The “R” group is a hydrocarbon only
How many amino acids are polar?
6
What does it mean for the “R” group if the amino acid is polar?
The “R” group contains elements that form a polar covalent bond (oxygen, nitrogen, or sulfur)
How many amino acids are polar due to a negative ionizing charge?
2
What does it meant for the “R” group if the amino acid is polar due to a negative ionizing charge?
the “R” group acts as an acid
How many amino acids are polar due to a positive ionizing charge?
3
What does it mean for the “R” group if the amino acid is polar due to a positive ionizing charge?
The “R” group acts as a base
What contains the genetic code for proteins?
DNA
What is the primary structure of a protein?
The number and sequence of amino acids held together by peptide bonds
What is the sequence of amino acids determined by?
A gene
What does the sequence of amino acids determine?
Which intramolecular bonds will form (therefore the 3D shape of the protein)
When would the “R” groups not influence the shape of the protein molecule?
If all the “R” groups are non-polar
What do all amino acids have even if their “R” groups do not?
charges
Where do amino acids’ charges come from if the “R” groups are non-polar?
The amine groups and carboxyl groups that make up peptide bonds
What are residues?
Carboxyl groups joining with amine groups
What are the two possible shapes that can result when the primary structure of a protein contains only non-polar “R” groups?
beta-pleated sheet and alpha helix
What are the beta-pleated sheet and alpha helix held together by?
hydrogen bonds
What is all the hydrogen bonding between in beta-pleated sheets and alpha helixes?
non-adjacent amine and carboxyl residues
What is the only possible way for hydrogen bonds to form with non-polar “R” groups?
to shape itself into beta-pleated sheets and alpha helixes
What do proteins with purely a beta-pleated sheet or alpha helix shape never form?
a complex or unique globular shape
What are fibrous proteins?
Proteins that have polypeptide chains which are mostly insoluble in water due to its non-polar amino acids
What do fibrous proteins have function related to?
movement
What are two examples of fibrous proteins?
actin and myosin
What will amino acids with a carboxyl in their “R” group do?
They will dissociate, lose the hydrogen ion and become negatively charged
What will amino acids with an amine within their “R” group do?
They will bind to a hydrogen ion and become positively charged
What can two oppositely charged “R” groups do?
Form an ionic bond between each other
What is a hydrophobic interaction?
Non-polar amino acids will fold into an area within the interior of the polypeptide in an attempt to avoid the water molecules
What do cysteine’s “R” groups contain?
a sulfur atom bonded to a hydrogen atom
What happens when two non-adjacent cysteine amino acids get close to each other?
The two hydrogens can be removed and the two sulfur atoms become covalently bonded to each other
What kind of bond is the strongest of all the bonding forces that influence polypeptide shape?
disulfide bond
What is a disulfide bond?
The two hydrogens being removed and the two sulfur atoms becoming covalently bonded together (in cysteine amino acids)
Polar amino acids will form what kind of bond with each other?
hydrogen bonds
Why are polar amino acids often found on or near the exterior of the polypeptide?
Because of their hydrophilic properties
What kind of bond is typically the most numerous intramolecular type of bond?
Hydrogen bonds
What are four of the bonding interactions that can occur at the tertiary level?
Ionized “R” groups forming ionic bonds, hydrophobic interactions, disulfide bonding, polar amino acids forming hydrogen bonds
Why do proteins composed of non-polar amino acids not need to be soluble?
They are primarily structural proteins that generally stay in place
How do proteins that have polar amino acids differ from proteins that have non-polar amino acids?
Rather than staying stationary, they are often found in different locations within the cell/body because they have better solubility
What is lipase?
An enzyme that catalyzes the hydrolysis of lipid molecules
What does the 3D shape of lipase allow?
a high concentration of hydrophobic amino acids to fold into the inside/core of the enzyme and a high concentration of hydrophilic amino acids on the outside of the molecule
What permits lipase to be soluble in a water environment?
The outer polar amino acids allowed by its shape
How do glycoproteins A and B remain embedded in the phospholipid bilayer?
The protein portion of the molecules fold so that non-polar amino acids can interact with the hydrophobic layers of the membrane
What does the folding of the protein portion of glycoproteins A and B lead to?
polar amino acids bonding to the sugar component of the molecule and interacting with the aqueous blood plasma
What is the quaternary structure of a protein?
When two or more amino acid chains bond together into a single molecular structure
What is insulin?
a protein hormone secreted by cells of the pancreas
What is the function of insulin?
to promote glucose uptake by body cells
What is insulin when it is first synthesized by pancreatic cells?
a single chain of 110 amino acids
How is the initial insulin single chain of amino acids modified in pancreatic cells?
it becomes two chains of amino acids, one with 21 amino acids and the other with 30
What bonds are included in the two insulin chains becoming bonded together?
3 disulfide bonds
What are dimers?
Two insulin molecules temporarily bonded together
Why is insulin inactive while in the pancreas cells?
due to the dimers formed
What is a hexamer?
Three dimers bonded together
What shows the quaternary structure in insulin?
The dimers and hexamers
What happens for insulin to become active as a hormone?
The dimers and hexamers separate for insulin to become a monomer
What is the most abundant protein in the human body?
Collagen
What are the functions of collagen?
make up connective tissue, provide tensile strength to tendons and ligaments, give elasticity to skin
What is the structure of collagen?
fibrous protein consisting of three polypeptide chains wound around each other in a helix shape
What give collagen its quaternary structure?
The arrangement of the three polypeptide chains
What is haemoglobin?
a large protein found within red blood cells
What is the function of haemoglobin?
to bind reversibly to oxygen in the lungs and carry oxygen to body tissues, also to bind reversibly to carbon dioxide to be taken to lungs and exhaled
What is haemoglobin an example of?
a conjugated quaternary structured protein
How does haemoglobin exhibit each of the three types of protein structures?
It has two different primary structures, a secondary structure seen in the alpha helix structures within portions of the polypeptides, a tertiary structure in each of the four globular polypeptides which fold and containe intramolecular bonds, and quaternary structure with the four polypeptides bonding into the single molecule
What is the general rule of fibrous protein functions vs. globular protein functions?
Fibrous proteins have a structural function while globular proteins have very specialized functions
What are some examples of the specialized roles of globular proteins?
enzymes, antibodies, peptide hormones, cell signalling proteins
What kind of protein is collagen?
fibrous
What gives collagen its very regular and geometric fibrous shape?
short repeating sequences of amino acids
Why is collagen a good molecule for building tissues in the body?
Because of its structural uniformity
What kind of protein is insulin?
A globular protein
How can globular proteins be specialized for a specific purpose?
Due to their wide variety of amino acids within their structure
When is insulin released into the bloodstream?
after blood glucose levels rise, usually after eating something with carbohydrates
What are insulin receptors?
Membrane proteins on each body cell
What happens to insulin molecules as they reach the body cells?
They fit into the insulin receptor proteins
What is a signal pathway?
A set of reactions that occur when insulin fits into the membrane receptor
What is the end result of a signal pathway?
the cell opens channels in the plasma membrane that allow glucose to enter the cell
Why is glucose needed in a cell?
For cellular respiration
