How Cells work - The Molecules Flashcards
Heterodimers
Heterodimers means 2 different molecules joined together
Homodimer
Homodimer means 2 of the same molecules joined together.
Protein p53 molecule
Protein p53 molecule is important in cell cycle regulation and hence pathological consequence of cancer progression.
P53 binds to DNA at a very specific sequence as a tetramer. P53 is a homotetramer - four identical subunits. Common theme for DNA binding proteins.
Multimer
Multimer is an aggregate of multiple monomers, that is held together by non-covalent bonds.
Polymer
Polymer is a series of monomers that are held together with covalent bonds.
Oligomer
An oligomer is an intermediate length polymer, typically more than 10 sub-units, but is not a precise term.
Proteins
Proteins are polypeptides of amino acids
They contain an amino group, an alpha carbon, an R group and a carboxyl group
R groups
The R group determines the amino acid.
R groups have different sizes, shape and chemistry that contribute to structure and protein function.
How do amino acids join together?
Amino acids join together independent from the R group via a condensation reaction (which releases H2O molecule) between the electrophilic carboxyl group and the H atom of the amino group. The result is a formation of a peptide bond between the C and N atom of the corresponding amino acids.
Where does condensation reactions of amino acids occur?
This reaction occurs in the ribosome which are made up of RNA (rRNA) so it shows that reaction do not have to occur by enzymatic proteins.
Nucleoside
A pentose sugar joined to a base makes a nucleoside,
A pentose sugar attached to a base is called what?
Nucleoside
Types of RNA in cells
mRNA
tRNA
rRNA
Glycogen
Mainly stored in liver and muscle
Glycogen storage disease cause by defects in different enzymes.
a(1-4) glycosidic bonds link monomers
a(1-6) glycosidic bonds form branches
Contains reducing ends
How can proteins be modified?
Proteins can be modified by addition of sugar chains by the covalent bond the N-linked or O-linked glycosylation.
O-linked glycosylation of proteins
O linked (serine or threonine)
Blocks other modifications.
Proteoglycans
Proteins with a sugar attached (a specific type of sugar and linkage). Proteoglycans are very large molecules. Sugar chains are negatively charged so expand.
Proteoglycans (mucoproteins) are formed of glycosaminoglycans (GAGs) covalently attached to the core proteins. They are found in all connective tissues, extracellular matrix (ECM) and on the surfaces of many cell types.
Proteoglycans have much more carbohydrate content than glycoproteins.
Lipids and Fatty Acids
Fatty acids (CO2H) + glycerol = mono, di and triglyceride
Fats and sterols, vitamins A, D, E and K
Phospholipids are critical in membranes
Essential and non-essential
High energy content, so stored in adipocytes
Vital for membrane structure and cell signalling.
Gases in Human Biology
Blood pressure and vascular tone
Angina and erectile dysfunction
Activation of enzymes and cellular signalling
Haem synthesis
Detoxification
Types of protein structure
Primary Structure
Secondary Structure
Tertiary Structure
Quaternary Structure
Primary Structure
The primary structure is the number, type and sequence of amino acids. The peptide starts to form as soon as it is synthesised forming the secondary structure.
Two Major Protein Secondary Structure Motifs
The alpha helix (a-helix) and the anti-parallel beta sheet (B-sheet).
The alpha helix
Hydrogen-bonded networks
Can transverse membranes
Side chains (R-groups) dictate helix function.
Tertiary Structure
This is the next level up, where the secondary structure folds to assemble the complex functional molecule. Tertiary structure are stabilised by non-covalent interactions (hydrogen bond, hydrophobic interactions, ionic ‘salt’ interactions) and covalent interactions (cys-cys disulphide bonds).
Quaternary Structure
Myoglobin (monomer) is folded to form a tertiary structure which then assembles a tetramer complex, that is the quaternary structure of functional haemoglobin.
Quaternary structure is a protein with 2 or more polypeptides.
Structure and Function in Haemoglobin
Iron binding through nitrogen atoms (coordinate bonds).
When oxygen binds to haemoglobin, the iron atom moves. This is the confirmational change that takes place when oxyhaemoglobin is converted into deoxyhaemoglobin. This is known as cooperative allostery, which occurs through binding of oxygen to each of the four sites of the tetramer structure to induce a confirmational change that makes it easier for the next oxygen to bind to the haem groups. Haemoglobin has a sigmoidal response to oxygen-oxygen binding.
