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Summary All the information for topic 2 of IB Biology SL
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- Bachillerato
All the information for topic 2 of IB Biology SL
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Molecular biology2.1 Molecules to metabolism
Essential idea:
Living organisms control their composition by a complex web of chemical reactions
Molecular biology
It is a science that studies inorganic and organic molecules
Molecular biology is the study
and the process in which they are involved. All living
of the molecular basis of
organisms control their composition through a complex
biological activities in cells.
web of chemical reactions that form the basis of life.
Every aspect and structure of living cells is the result
of chemical reactions. Basically, it studies how the cell works
in a reductionist approach (each of the metabolic reactions of
the cell at a time instead of studying the whole picture).
Since the structure of DNA was discovered, Molecular
Biology has transformed the understanding of living
processes. This is because of the relationship between genes
and the polypeptides they generate.
Þ DNA à RNA à Proteins
This process cannot be reversed and the protein generated cannot change the RNA or DNA.
Organic molecules Inorganic molecules
Carbon based (with H)
Present on living materials only Can be present in non-living things as well
Ex: glucose Ex: water, CO2
Carbon
Living organisms contain a vast range of chemical substances, the majority of which
are carbon-containing compounds such as glucose, fats, and proteins. These are collectively
,known as organic compounds. However, there are a few carbon compounds that are not
considered to be organic, such as carbon dioxide, carbon monoxide, carbonates, and hydrogen
carbonates.
They can be formed as monomers, polymers, and
cellular structures
Þ Organic compounds in cells:
• carbohydrates
• nucleic acids
• proteins
• lipids
Carbon has the atomic number 6, which means
that it has 4 electrons in its outer shell and
can form four covalent bonds with other
atoms. This allows a diversity of stable
carbon compounds to exist. Many
important macromolecules are composed of
long carbon chains or rings. Other molecules
can be simple in their structure, such as
methane, which consists of a single carbon
atom and four hydrogen atoms.
Organic compounds in cells • Check the functional groups:
Living organisms are made of organic o Presence of -COOH, (carboxyl group)
compounds called macromolecules. There are and -NH2, (amine group), implies the
four types of macromolecules: carbohydrates, monomer is an amino acid.
Presence of -COOH attached to a
lipids, proteins, and nucleic acids. All of them
o
long hydrocarbon chain implies the
contain Carbon, Hydrogen, and Oxygen atoms.
monomer is a fatty acid.
Nitrogen appears in proteins and nucleic acids,
and phosphorus in some lipids (phospholipids).
Macromolecules build living cells and take part in
numerous biochemical reactions. • Check if the number of hydrogen and
• Carbohydrates are macromolecules oxygen is in the ratio of 2:1; this implies the
monomer is a sugar. You then count the
composed of three elements: Carbon,
carbon atoms to identify if it is ribose (5
Hydrogen, and Oxygen. The ratio of
carbon) or glucose (6 carbon).
hydrogen to oxygen is 2:1.
, • Lipids are a very diverse group of organic compounds. They include steroids (e.g.
cholesterol), waxes, phospholipids and triglycerides.
• Proteins consist of amino acids that are arranged in long chains.
• Nucleic acids are also chains but formed by nucleotides.
Macromolecules are made up of smaller monomers. Monomers are like building bricks, they join
together to form larger structures called polymers.
Macromolecule Name Drawing Function
Carbohydrates
Alpha-D- Used in the production
• They contain glucose of ATP in cells.
carbon,
hydrogen, and (hexose, not
because it is an
oxygen
hexagon)
• Organic
compounds Beta-D- Used to build cell walls
consisting of glucose in plants.
more simple
sugars Formula for all
types of
• Monomers
glucose:
follow the
C6H12O6
general formula
Starch Used as long-term
of (CH2O)x
Glucoses storage in plants.
• Monomers are
together,
commonly ring- branched
shaped
Ribose Used as a component
molecules
of DNA and RNA.
, Lipids
Triglycerides Used as long-term
• Contain carbon, storage in adipose
hydrogen and tissue in animals.
oxygen Composed by a glycerol
• Lipids are a and fatty acids
group of organic Have a hydrophilic
molecules that head and hydrophobic
are insoluble in tails.
water but Steroids Used as chemical
soluble in non- messengers in the
polar organic (They only ask body, have a distinctive
solvents. you about ring shape. They are
cholesterol)
also important in
membrane structure.
Phospholipids Major component of
plasma membranes.
Proteins
Structural Proteins such as
• Contain carbon, proteins keratin and collagen
hydrogen, form the structural
oxygen and framework of many
nitrogen (Sulphur parts of the body.
is also common Enzymes Metabolic proteins that
but not present speed up chemical
in all proteins) reactions in the body.
• Proteins are Polypeptides A sequence of amino
large organic acids that may make up
compounds a protein, or a series of
arranged into polypeptides can also
make up a protein.
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