How Cells work - The Molecules

Question 1

Heterodimers

Answer 1

Heterodimers means 2 different molecules joined together

Question 2

Homodimer

Answer 2

Homodimer means 2 of the same molecules joined together.

Question 3

Protein p53 molecule

Answer 3

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.

Question 4

Multimer

Answer 4

Multimer is an aggregate of multiple monomers, that is held together by non-covalent bonds.

Question 5

Polymer

Answer 5

Polymer is a series of monomers that are held together with covalent bonds.

Question 6

Oligomer

Answer 6

An oligomer is an intermediate length polymer, typically more than 10 sub-units, but is not a precise term.

Question 7

Proteins

Answer 7

Proteins are polypeptides of amino acids
They contain an amino group, an alpha carbon, an R group and a carboxyl group

Question 8

R groups

Answer 8

The R group determines the amino acid.
R groups have different sizes, shape and chemistry that contribute to structure and protein function.

Question 9

How do amino acids join together?

Answer 9

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.

Question 10

Where does condensation reactions of amino acids occur?

Answer 10

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.

Question 11

Nucleoside

Answer 11

A pentose sugar joined to a base makes a nucleoside,

Question 12

A pentose sugar attached to a base is called what?

Answer 12

Nucleoside

Question 13

Types of RNA in cells

Answer 13

mRNA
tRNA
rRNA

Question 14

Glycogen

Answer 14

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

Question 15

How can proteins be modified?

Answer 15

Proteins can be modified by addition of sugar chains by the covalent bond the N-linked or O-linked glycosylation.

Question 16

O-linked glycosylation of proteins

Answer 16

O linked (serine or threonine)
Blocks other modifications.

Question 17

Proteoglycans

Answer 17

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.

Question 18

Lipids and Fatty Acids

Answer 18

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.

Question 19

Gases in Human Biology

Answer 19

Blood pressure and vascular tone
Angina and erectile dysfunction
Activation of enzymes and cellular signalling
Haem synthesis
Detoxification

Question 20

Types of protein structure

Answer 20

Primary Structure
Secondary Structure
Tertiary Structure
Quaternary Structure

Question 21

Primary Structure

Answer 21

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.

Question 22

Two Major Protein Secondary Structure Motifs

Answer 22

The alpha helix (a-helix) and the anti-parallel beta sheet (B-sheet).

Question 23

The alpha helix

Answer 23

Hydrogen-bonded networks
Can transverse membranes
Side chains (R-groups) dictate helix function.

Question 24

Tertiary Structure

Answer 24

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).

Question 25

Quaternary Structure

Answer 25

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.

Question 26

Structure and Function in Haemoglobin

Answer 26

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.