Biological Molecules Lesson BWHS

Biological Molecules

Jeffrey Reed

A Nucleic Acid Amplification Test, or
NAAT, is a type of viral diagnostic test
for SARS-CoV-2, the virus that
causes COVID-19.

NAATs detect genetic material
(nucleic acids). NAATs for
SARS-CoV-2 specifically identify the
RNA (ribonucleic acid) sequences that
comprise the genetic material of the
virus.

Molecular Testing

Organic molecules

What is a human made of?

The most abundant compound in our
bodies is water, which makes up around
62% of our total body mass. About 16% is
protein, another 16% is fat, and around
1% is carbohydrate.

Large organic molecules
are usually made up of lots
of similar smaller
molecules called subunits.

The subunits can be split apart by a reaction called hydrolysis, which uses water.

They can be joined together again, perhaps in new combinations, by a reaction called
condensation, which produces water.

CONDENSATION

Carbohydrates

These may be simple, soluble sugars or complex materials like starch and
cellulose, but all carbohydrates contain carbon, hydrogen and oxygen only.

Monosaccharides are the simplest carbohydrates, for example, glucose.

Glucose is soluble so it is easily transported in blood and dissolves in the cytoplasm
of cells. Monosaccharides are the main source of energy for many cells.

C6H12O6

Polysaccharides are formed from many monosaccharide molecules –
for example, starch and glycogen.

Polysaccharides are insoluble, so they are good stores of energy.

Lipids

Fats (which are solid at room temperature) and oils (which are liquid at room
temperature) are made of molecules called lipids. They are insoluble in water.
Fats and oils are formed from carbon, hydrogen and oxygen only.

Lipids are formed by the condensation of three molecules offatty acid
with one molecule of glycerol .

饱和脂肪酸

不饱和脂肪酸

Lipids are excellent stores of energy.
Lipids yield 9 kcal of energy per gram
while carbohydrates and proteins yield
only 4 kcal of energy per gram.

Lipids form barriers between watery
environments, such as between a cell
and its surroundings.

Proteins

Although there are many different types of protein, all
contain carbon, hydrogen, oxygen and nitrogen, and
maybe sulfur. Their molecules are made up of long chains
of simpler chemicals called amino acids.

The 20 different amino acids can be joined together in a vast number of different orders, and
some proteins are thousands of amino acids long.

The sequence of amino acids determines
the shape of the protein molecule – some
are long and thin (such as keratin).

Nucleic acids 核酸

Nucleic acids are the information-carrying
molecules of the cell. The two main classes
of nucleic acids are deoxyribonucleic acid
(DNA) and ribonucleic acid (RNA).

A Nucleic acid molecule is
made up of long chains of
nucleotides.

Step 1 Condensation: Form a nucleotide

Step 2 Condensation: Form a chain

The phosphate and
sugar molecules
are the same all the
way down the chain
but the bases may be
any one of the four.

*Testing for biochemicals

The fact that lipids are insoluble forms the basis of
a physical test–emulsion test:

■ 2 cm3 of ethanol are added to the unknown
solution, and the mixture is gently shaken.

■ The mixture is poured into a test tube containing
an equal volume of distilled water.

■ If a lipid is present, a milky-white emulsion is
formed.

To test for protein, a few drops of
Biuret reagent are added to 2 cm3
of the unknown solution, and the
mixture is gently shaken.

A purple colour is a positive result
(protein is present).

To test for starch, a few drops of
iodine solution are added to 2
cm3 of the unknown solution, and
the mixture is gently shaken. A
deep blue-black colour is a positive
result (starch is present).

To test for glucose, 2 cm3 of Benedict’s reagent are added to
2 cm3 of the unknown solution, and the mixture is heated in a
boiling water bath for 2–3 minutes. An orange/brick-red colour is
a positive result (glucose is present).