2.7 Proteins Flashcards
What is a protein?
a polymer composed of amino acid monomers
What is an amino acid?
an organic molecule composed of a central carbon atom bonded to a hydrogen atom and 3 functional groups
- amino group (–NH2)
- acidic group (–COOH)
- ‘R’ group
What does the ‘R’ group of an amino acid determine?
the uniqueness of each amino acid
What is the ‘R’ group of an amino acid?
varies from having a single carbon to being a complicated ring structure
What is keratin?
structural protein that makes up hair and nails
What is collagen?
structural protein that lends support to ligaments, tendons, and skins
What are enzymes?
proteins that speed up chemical reactions and are necessary contributors to the chemical workings of the cell, and the body
What are hormones?
proteins that are messengers that influence cellular metabolism
What are actin and myosin?
proteins that account for the movement of cells and the ability of our muscles to contract
What is hemoglobin?
a complex protein in our blood that transports oxygen
What are antibodies?
proteins in blood and other body fluids that combine with foreign substances, preventing them from destroying cells and upsetting homeostasis
What are the functions of proteins in the plasma membrane of cells?
- some form channels that allow substances to enter and exit cells
- some are carriers that transport molecules into and out of the cell
- some are enzymes
What does the synthesis reaction between two amino acids result in?
a dipeptide and a molecule of water
What is a polypeptide?
a chain of amino acids that are joined to one another by a peptide bond
What is a peptide bond?
a type of bond that joins amino acids together in a polypeptide
Why do the atoms associated with a peptide bond unevenly?
because oxygen is more electronegative than nitrogen
- the hydrogen attached to the nitrogen has a slightly positive charge
- oxygen has a slightly negative charge
What does the polarity of the peptide bond mean?
hydrogen bonding is possible between the C=O of one amino acid and the N-H of another amino acid in a polypeptide
What does hydrogen bonding influence in proteins?
structure/shape of a protein
What are the 4 levels of protein organization?
primary
secondary
tertiary
quaternary
What is the primary structure?
the linear sequence of the amino acids joined by peptide bonds
How do polypeptides differ from one another?
a polypeptide chain is made from 20 different amino acids, each with its own sequence of amino acids and its own sequence of ‘R’ groups
How does the secondary structure come about?
when the polypeptide takes on a certain orientation in space
What are the 2 possible shapes of the secondary structure?
alpha helix
beta pleated sheet
What causes the polypeptide to form a alpha helix or beta pleated sheet?
hydrogen bonding between amino acids
What results in an alpha helix?
a coiling of the chain
What results in a beta pleated sheet?
a folding of the chain
What is the tertiary structure?
the final 3D shape of a protein
What shape do myosin molecules in muscles have?
a rod shape ending in globular heads
What shape do enzymes have in the tertiary structure?
the polypeptide bends and twists in different ways
Where are hydrophobic and hydrophilic portions in the tertiary structure?
hydrophobic: packed mostly on the inside
hydrophilic: on the outside where they can make contact with water
How is the tertiary shape of a polypeptide maintained?
by various types of bonding among the ‘R’ groups: covalent, ionic, and hydrogen bonding all occur
What is a common form of covalent bonding between ‘R’ groups?
a disulfide (S-S) linkage between 2 cysteine amino acids
How do proteins differ from one another?
- the number of polypeptides (each with its own primary, secondary, and tertiary structure)
- length
- sequence
- structure
What gives the tertiary structure a characteristic globular shape?
the polypeptide folds and twists due in part to covalent bonding between ‘R’ groups
What is the quaternary structure?
occurs when 2 or more polypeptides join to form a single protein
in proteins with multiple polypeptide chains, these separate polypeptides are arranged to give such proteins a fourth level of structure
ie. hemoglobin and most enzymes
Why is the final shape of a protein very important to its function?
- enzymes cannot function unless they have their normal shape
- ONCE A PROTEIN LOSES ITS NORMAL SHAPE, IT IS NO LONGER ABLE TO FUNCTION NORMALLY
What does ‘denatured’ mean?
describes a protein that has had an irreversible change in its shape due to exposure to extremes in heat and pH
Give examples of denaturation?
- adding acid to milk causes curdling
- heating causes egg white (contains a protein called albumin) to coagulate
Why does denaturation occur?
becasue the normal bonding between the ‘R’ groups has been disturbed
What are prions?
structures formed by the alteration in protein organization and is related to the development of Alzheimer’s diease and Creutzfeldt-Jakob disease (human ‘mad cow’ disease)
What is the ‘R’ group of the amino acid Alanine?
a single carbon
CH3
What is the ‘R’ group of the amino acid Valine?
a branches carbon chain
CH
/ \ H3C CH3
What is the ‘R’ group of the amino acid Cysteine?
contains sulfur
CH2
|
SH
What is the ‘R’ group of the amino acid Phenylalanine?
a ring structure
CH2
|
[hexagon]
What are waxes?
long chain fatty acid attached to an alcohol, solid at room temperature
What do waxes do?
protect from water (plants, ears) and energy storage in plankton
What test do you use to detect the presence of protein? What colours does it change to and from?
Biuret’s solution
blue to violet
