Download A look at macromolecules (Text pages 38

A look at macromolecules (Text pages 38-54)
What is the typical chemical composition of a
cell? (Source of figures to right: Madigan et al.
2002
Chemical Bonds
Ionic
• Electron-negativity differences cause unequal distribution of electrons essentially
creating ions. Molecules are held together by
electrical attraction...Na+ Cl• Not of major significance among the
important classes of bio-organic molecules
Covalent (bond strength > 50 Kcal mole-1)
• More-or-less equal sharing of electrons
between two atoms creating stable molecules
• Consequential in biological molecules
Hydrogen bonds (bond strength <2 kcal mole-1)
• Weak ‘charge’ based attraction between
molecules
• Very common in biological systems.
What are the major classes of biologically
important molecules?
Carbohydrates (Sugars)
• All have the general form CH2O
o Example: C6H12O6
• Can exist as
o Monomers
o Polymers
ƒ Monomers joined to form a
potentially very large
molecule.
ƒ Joined covalently by a
glycosidic bond
ƒ Sizes
• Disaccharides
• Trisaccharides
• Oligosaccharides
(several monomers)
• Polysaccharides
(many many
monomers)
•
o Uses
ƒ
ƒ
ƒ
Substituted forms
(sugar derivatives)
Structural components of
cells
• Nucleic acids
• Walls
Energy
Nature of the glycosidic
bond influences function
• Alpha form
• Beta form
• 1--> 4 bond
• 1--> 6 bond
o Why are these important?
ƒ Polymeric sugars serve as
energy reserves
ƒ Polymeric sugars are
structural components of
cells
ƒ They can form bonds with
lipids and proteins resulting
in otter complex structural
materials
• Glycolipids
• Glycoproteins
ƒ Many of which are on the
cell surface and act as
receptors.
Lipids and Fatty Acids
•
•
•
•
Fatty acids
o Long chain hydrocarbons with
a carboxylic acid at one end
and a methyl group at the other
o Variable chain length
o Variable degree of double
bond controls degree of
liquidity
o Hydrophobic end vs.
hydrophilic end
Simple lipids
o Fatty acids esterified to
glycerol
o Termed a neutral triglyceride
Complex
o Similar to triglyceride but
additional material substituted
to the glycerol backbone
o Very important biologically as
this modifies the polar nature
of the fatty acids
Uses
o Structural components of cells
o In some cases, energy reserves
Amino Acids and Proteins
•
Amino acids are the monomers
that comprise proteins (proteins
are poly-amino acids)
• 20 common amino acids and a
few unique to bacteria
• all have some things in common
o carboxylic acid end
o amino end
o can bond end to end
via the Peptide Bond
to form complex
molecules with three
dimensional
characteristics
Proteins
•
•
Forms
Structural (parts of physical nature of
cells)
• Catalytic (enzymes)
General convention of describing structure
• Primary : linear array of amino acids
•
Secondary: nature of twists and folds
o Alpha helix
o Beta pleated sheet
• Tertiary: continued folding post
secondary structure
• Quaternary: more than one
polypeptide chain
Structure determined by order of amino
acids
• Degree of hydrogen bonding
• Structure can be ‘denatured’
• Gentle vs. harsh
The concept of stereoisomers
In cells, the L-form of stereoisomers is the form that is
almost always in play.
Nucleotides and Nucleic acids
Nucleic acids
• Monomers are nucleotides
• Forms are
• DNA and RNA
Composition of nucleotides
• Ribose or deoxyribose
• Purine or pyrimidine base
• Phosphate
How does this come together?
• Nucleoside vs nucleotide
Uses
• As polymers that carry genetic
information
• Carriers of chemical energy
• Reduction and oxidation mediators
• Regulatory molecules carriers of sugars
for polysaccharide biosynthesis
As carriers of genetic information
• DNA
o Several million nucleotides in a
polymer
o Polymer double stranded
ƒ A-T bonds
ƒ G-C bonds
o Held by hydrogen bonding
o Strands are complementary and
anti-parallel (Figure in lower
right from: Lewin, B. 1990)
•
RNA
o All single stranded (except in some viruses)
o Can be highly folded and give the appearance of being double stranded
o Forms of RNA
ƒ Messenger (mRNA)
• Produced fro DNA template (i.e. complementary)
• Signal stranded
• Essentially ‘directs’ how amino acids are assembled to build
proteins
ƒ Transfer (tRNA)
• Carries appropriate amino acids from cytoplasm to mRNA
template
ƒ Ribosomal (rRNA)
• Mediates the assembly of a protein by interfacing with mRNA and
tRNA
Except where indicated, tables and figures used in this section are from Madigan et al. 2002.
References:
Madigan, M.T., J.M. Martinko, and J. Parker. 2002. Brock Biology of Microorganisms, 10th
ed. Prentice Hall.
Lewin, B. 1990. Genes, 4th ed. Cell Press Inc. Cambridge