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The chemical nature of the cell
1. 03. The chemical nature of the cell.
Ian Anderson (2013)
Saint Ignatius College Geelong
2. Knowledge and skills.
Distinguish between organic and inorganic molecules.
Describe the roles of biologically important inorganic
molecules.
Outline the properties of water that are important to
life.
Describe the basic structures of carbohydrates, lipids,
proteins and nucleic acids.
3. Organic v inorganic molecules.
Chemical compounds can be divided into two groups.
Organic compounds.
Most carbon containing compounds are organic.
e.g. methane (CH4) and glucose (C6H12O6).
But not all e.g. carbon dioxide(CO2).
Therefore our definition:
Compounds that contain both carbon and hydrogen
Inorganic compounds.
All other molecules that do not contain both carbon and
hydrogen.
4. Components of cells.
The molecules that make up living organisms can be
grouped into five classes
Water
Carbohydrates
Lipids
Biomacromolecules
Proteins
Nucleic acids.
5. Water.
H2O = inorganic compound.
Most abundant compound in living organisms
Most organisms 70-90% water
Humans – females ~50%; males ~60%; newborn babies
~75%
Unique properties of water help explain why it is so
important to life:
Molecules stick together (as a result of H bonding)
A good solvent
Heat capacity
6. Biomacromolecules.
Very large organic molecules.
All are polymers (except lipids).
Polymers are made up of many smaller building blocks
called monomers.
(poly = many; mono = single; mer = segments).
The monomers in a polymer are joined by a dehydration
(condensation) reaction (where water is released during
the reaction).
monomer + monomer polymer + H2O
(Reverse reaction = hydrolysis reaction)
7. Carbohydrates.
Organic compounds.
Most abundant organic compounds in nature.
Made up of carbon, hydrogen and oxygen.
Energy rich – source of energy for all living organisms.
Also important in plants as structural material
(cellulose).
Exoskeleton of insects (chitin)
8. Carbohydrates.
Basic unit of carbohydrates are the simple sugars –
monosaccharides (CnH2nOn)
e.g. glucose (C6H12O6).
Disaccharides – two monosaccharide sugars joined
together (also called simple sugars)
e.g. sucrose
Polysaccharides – many simple sugars (monomers)
joined together to form long chains (polymer).
Also called complex carbohydrates.
e.g. starch, glycogen, cellulose.
9. Lipids.
General term for fats, oils and waxes.
But also include phospholipids, steroids, glycolipids and
carotenoids.
Composed of carbon, hydrogen and oxygen, but in
different proportions to carbohydrates (less oxygen &
often contain other elements such as phosphorus and
nitrogen).
All lipids are hydrophobic and insoluble in water.
Lipids are not polymers.
10. Types of lipids.
Triglycerides (fats & oils).
Known as simple lipids (composed only of C, H & O, but in
different proportions to carbohydrates).
Important energy storing molecules.
Fats store twice as much energy as the same weight of carbohydrates.
Made up of a glycerol molecule and three fatty acid
molecules.
Fatty acids may be either saturated (no double bonds) or
unsaturated (contains double bonds), which is important for
determining the fluidity and melting point of the lipid.
Fats (which are solid at room temperature) have many more
saturated bonds than oils (which are liquid).
11. Types of lipids.
Triglycerides (fats & oils).
Source: Enger et al. (2011)
12. Types of lipids.
Phospholipids.
Known as complex lipids (also composed of C, H &
O, but also other elements such as P & N).
Similar in structure to triglycerides, except that one of
the three fatty acids attached to glycerol is replaced by a
phosphate containing group.
Structure results in a hydrophilic, polar head (soluble in
water) and a hydrophobic, non-polar tail (insoluble in
water).
Phospholipids are a major component of cell
membranes.
13. Types of lipids.
Phospholipids.
Source: Campbell et al. (2011)
Source: Enger et al. (2011)
14. Types of lipids.
Steroids.
Have a very different structure than other lipids.
Four interlocking rings of carbon.
Still have large number of carbon-hyrogens, and are non-
polar.
Important examples include cholesterol, the sex
hormones (testosterone, oestrogen and cortisol) and
vitamins such as Vitamin D.
Waxes.
Important role in both plants and animals for their
ability to form a waterproof coating.
15. Proteins.
Large molecules made up of amino acids.
20 naturally occurring amino acids.
Joined together by peptide bonds (as a result of a
hydration reaction).
To form a polypeptide.
Contain nitrogen, as well as carbon, hydrogen and
oxygen (some also contain sulphur, phosphorus and
other elements).
Proteins are unique to each type of organism.
16. Proteins.
Amino acids (the monomers of proteins).
All amino acids share a common structure
Amino group.
Carboxyl group.
Central α (alpha) carbon, and a
R group (also called the side chain).
Only the R group differs between amino acids.
17. Protein structure.
Proteins are very complex, with four levels of
complexity used to describe them.
Primary.
Secondary.
Tertiary.
Quaternary.
18. Protein structure.
Primary structure.
The sequence of amino acids in the polypeptide chain.
The polypeptide chain is the result of dehydration reactions
between the carboxyl group of one amino acid and the amino
group of another, resulting in peptide bonds.
The amino acid sequence determines what three-
dimensional shape the protein will have.
The specific sequence of amino acids in a polypeptide is
controlled by the genetic information of the organism.
Source: Enger et al. (2011)
19. Protein structure.
Secondary structure.
Hydrogen bonding between the amino groups and the
carboxyl groups in a polypeptide can result in
α-helices (coils)
β-pleated sheets (folds), or
random coils (no distinct pattern).
Source: Enger et al. (2011)
20. Protein structure.
Tertiary structure.
The overall three-dimensional shape of the protein.
A polypeptide chain can contain one or more
combinations of α-helices and β–pleated sheets, causing
the chain to twist, bend and loop.
The result is interactions between the various side
chains (R groups) of the amino acids, incl
Hydrogen bonding, ionic bonding, covalent bonding (e.g.
disulphide bridges between two cysteine side chains),
hydrophobic interactions, etc.
Chaperone proteins (found in cells) help proteins fold
into their normal shape.
21. Protein structure.
Tertiary structure.
Interactions between the side chains in the
tertiary structure of a protein.
Source: Campbell et al. (2011)
Tertiary structure of a protein.
Source: Enger et al. (2011)
22. Protein structure.
Quaternary structure.
Two or more polypeptide
chains, each with their own
tertiary structure, joined
together as one functional
macomolecule.
e.g. Haemoglobin (4 polypeptide
chains), insulin (2 polypeptide
chains), immunoglobulins (4
polypeptide chains).
Source: Enger et al. (2011)
23. Proteins.
Two major types of proteins.
Fibrous proteins
The secondary structure (either α-helices or β-pleated sheets)
forms the dominant structure of the protein (i.e. generally
only have primary and secondary structure).
Are insoluble in water.
Play a structural or supportive role in the body.
e.g. keratin, collagen, silk, muscle and ciliary proteins.
Globular proteins
Are soluble in water.
All have tertiary and some have quaternary structure .
e.g. enzymes and hormones.
24. Proteins.
Proteins have any different functions, incl.
Structural
Collagen
e.g. collagen, keratin, etc.
Regulatory
Enzymes e.g. pepsin, catalase, etc.
Hormones e.g. insulin, glucagon, etc.
Carrier molecules (transport)
e.g. Haemoglobin.
Source: Reece et al. (2011)
25. Nucleic acids.
The genetic material of all life.
Made up of long chains of monomer units called
nucleotides.
Two types
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA).
(We look at these in more detail later, so just an
introductory look for now.)
26. Nucleic acids.
Each nucleotide (the monomer) is made up of three
parts
a sugar
a phosphate group, and
a nitrogenous base.
Source: Walpole et al. (2011)
27. Nucleic acids - DNA.
Double stranded and helical shape (double helix).
Sugar and phosphate groups form the backbone of the
ladder, while the bases form the steps.
The two strands are attached by hydrogen bonds
between their bases.
Sugar = deoxyribose.
Nitrogenous bases =
Adenine (A), cytosine (C), guanine (G) and thymine (T).
31. Other important compounds.
Vitamins
Organic compounds required by animals in very small
(trace) amounts for normal functioning.
Essential for many chemical reactions
e.g. Vitamin C are components of co-enzymes.
Minerals
Inorganic ions required by both animal and plant cells.
Play a role in metabolic process of cells.
