The chemical components of cells Flashcards
Which are the most abundant organic molecules in living cells?
Proteins
How much dry weight do proteins account for?
40 - 70 % of dry weight
Which groups do amino acids contain?
Carboxyl (-COOH) and amino (-NH2) groups
What are the two isomeric forms of amino acids?
L and D amino acids
Which amino acids are only found in proteins?
L-amino acids.
D-amino acids are rare in nature
How can the charge on an amino acid be varied?
By changing the pH. The pH at which the amino acid is uncharged is called the isoelectric point.
How many amino acids are commonly found in proteins?
20
What are proteins made up of?
Proteins are polymers built from amino acid monomers
What determines a protein’s primary structure?
The amino acid sequence
What determines a protein’s secondary and tertiary structures?
The interaction between the various side groups of amino acids
What determines a protein’s quartenary structure?
Combining more than one polypeptide chain
Five major categories of proteins
- Structural e.g. keratin
- Catalytic e.g. enzymes
- Transport e.g. haemoglobin
- Regulatory e.g. hormone
- Protective e.g. antibodies
What are special about enzymes?
They contain an active site, to which a specific substrate can bind during catalysis
What are the common form of enzymes?
Globular
What functional groups are between the amino acid monomers in a polymer?
Condensation reaction between amino acid monomers to form peptide bonds
The structure of hemoglobin
Hemoglobin is a conjugated protein. Contains additional groups amino acids. Made up of four iron-containing organometallic complexes (heme groups_
The two main groups of a protein’s secondary structure.
Secondary structure formed by the way in which polypeptide chain is extended. There are alpha helices or beta sheets
The action of antibodies
Antibodies are proteins that bind to specific molecules or portions of large molecules with high specificity. The antigen it bonds to is determined by the amino acid sequence at receptor sites. Binds to a foreign macromolecule called an antigen. Antibodies are Y-shaped. The combination of antibody and antigen is immune response.
The role of carbohydrates
Structural and storage compounds in cells and modulate certain chemical signals in cells
How are cabohydrates synthesised?
BY photosynthesis
CO2 + H20 + Light –> CH2O + O2
What are the two groups of monosaccharides?
Aldoses and Ketoses
What is the difference between an aldose and a ketose
The position of the carbonyl group.
In an aldose, carbonyl group on terminal carbon. In a ketose, carbonyl group on the next to terminal carbon
What is glucose - an aldose or a ketose?
It is an aldohexose
Common aldoses and ketoses
Aldose-Hexose - Glucose
Aldose - Pentose - Ribose
Ketose - Hexose - Fructose
Ketose - Pentose - Ribulose
The difference between deoxyribose and ribose sugars
Ribose contains one more OH group on pentagon structure
How are disaccharides formed?
By the condensation of two monosaccharides
Examples of disaccharides
Lactose and Sucrose
How are polysaccharides formed?
Condensation of more than two monosaccharides by glycosidic bonds
e.g. cellulose in plant cell walls
What is the major components of lipids?
Fatty acids. Chains of hydrocarbons (hydrophobic) with a carboxyl group (hydrophilic)
What are the primary components of membranes?
Lipids
How are fats formed from fatty acids?
Fats are esters of fatty acids.
How many fatty acids does a fat molecule contain?
Glycerol + 3 x fatty acids
How many fatty acid chains does a phosphoglyceride contain? And why are phosphoglycerides important?
Phosphoglycerides are formed by the esterification of 2 fatty acids with glycerol and a phosphate esterified to one of the glycerol components.
Why are membranes selectively permeable?
Cells must control the entry and exit of molecules into the cell.
Describe the lipid bilayer of a membrane
There is a phospholipid bilayer. The hydrophobic tails of the phospholipids form the core of the membrane and the hydrophilic heads form the outside of the membrane to associate with cytosol (liquid inside the cell)
What is the most common membrane phospholipid?
Phosphatidylcholine
The structure of a lipid
top to bottom
choline
phosphate
glycerol
2 x fatty acid chains
What are the functions of proteins in cell membrane?
Transport molecules through the cell membrane. (including in active transport)
What are the functions of steroids?
They are regulators in animal development and metabolism
Examples of steroids
testosterone (hormone)
cortisone (anti-inflammatory for arthritis)
