Download Macromolecules: Proteins and Nucleic Acids

• Some atoms
share outer
shell electrons
with other
atoms, forming
covalent bonds
• Atoms joined
together by
covalent bonds
form molecules
• Molecules can
be represented
in many ways
Table 2.8
Life on earth is based on carbon
A carbon atom forms four covalent bonds
It can join with other carbon atoms to
make chains or rings
Carbon skeletons vary in many ways
Ethane
Propane
Carbon skeletons vary in length.
Butane
Isobutane
Skeletons may be unbranched or branched.
1-Butene
2-Butene
Skeletons may have double bonds, which can vary in location.
Cyclohexane
Benzene
Skeletons may be arranged in rings.
3.6 Forming Macromolecules
Fig. 3.17
•
An organic molecule consists of a
carbon-based core with functional
groups attached
•
Functional groups are the groups of
atoms that participate in chemical
reactions
•
A relatively small number of structural
patterns underlies life’s structural and
functional diversity
Ethane
Flammable gas
Ethanol
Makes you drunk
3.6 Forming Macromolecules
• Cells make a huge number of large molecules from a small set of small
molecules
• Most of the large molecules in living things are macromolecules called
polymers
• Polymers are long chains of smaller molecular units called monomers
• Organisms are primarily made of four kinds of macromolecules
–
–
–
–
Proteins
Nucleic acids
Carbohydrates
Lipids
• Macromolecules are
made by a process
termed dehydration
synthesis
• Macromolecules are
broken down by a
process termed
hydrolysis
Fig. 3.18a
Fig. 3.18b
H2O
HO
H HO
H2O
H
HO
H
Energy
HO
H
Energy
HO
H HO
• Both types of processes require enzymes
H
3.7 Proteins
Fig. 3.19
• Made up of
subunits called
amino acids
Six amino
acids
• There are 20
common amino
acids, and they fall
into one of four
general groups
Six amino
acids
Five amino
acids
Three amino acids
Each amino acid contains:
– an amino group
– a carboxyl group
– an R group, which distinguishes each of the 20
different amino acids
Amino
group
Carboxyl (acid)
group
Amino acids monomers
can be linked by peptide bonds
Carboxyl
group
Amino
group
PEPTIDE
BOND
Dehydration
synthesis
Amino acid
Amino acid
Dipeptide
Protein Structure
• Determined by the sequence of its amino
acids
• There are four general levels
– Primary
– Secondary
– Tertiary
– Quaternary
Fig. 3.21 Levels of
protein structure
Atoms are shown as balls in
this space-filing model.
The protein’s shape (yellow)
fits into the grooves of DNA.
The protein is a “repressor”
that inhibits transcription
of a gene.
Protein Structure
• Primary structure
– The specific amino acid sequence of a protein
• Secondary structure
– The initial folding of the amino acid chain by
hydrogen bonding
• Tertiary structure
– The final three-dimensional shape of the protein
• Quaternary structure
– The spatial arrangement of polypeptides in a
multi-component protein
More info (not on exam)
•
A typical protein contains 200–300 amino acids
some are much smaller (smallest are peptides)
-some much larger (titin a protein in skeletal and
cardiac muscle contains 26,926 amino acids
in a single chain!)
-
Protein Structure
• Changes in a
protein’s
environment can
cause a protein
to denature
– It loses its threedimensional
structure
– And becomes
inactive
Fig. 3.22
Chaperone Proteins
• Help newly-produced proteins to fold properly
Fig. 3.25
• Chaperone protein deficiencies may play a role in
certain diseases like Alzheimer’s
Proteins are the most structurally and
functionally diverse of life’s molecules
• Proteins are involved in
– cellular structure
– movement
– defense
– transport
– Communication
• Enzymes are proteins,
but not all proteins are enzymes
A
3.8 Nucleic Acids
•
Long polymers of repeating subunits termed nucleotides
•
Nucleic acids such and DNA and RNA serve as the blueprints for proteins
•
They ultimately control the life of a cell
•
A nucleotide is composed of three parts
– Five-carbon sugar
– Nitrogen-containing base
– Phosphate
Fig. 3.26 The structure of a nucleotide
Nitrogenous bases
Space-filling
model
Fig. 3.28
The DNA
double helix
DNA
(Deoxyribonucleic acid)
RNA
(Ribonucleic acid)
Sugar = Deoxyribose
Sugar = Ribose
Bases = A, G, C, T
Bases = A, G, C, U
Double-stranded
Single-stranded
• Stretches of a DNA molecule called genes
program the amino acid sequences of
proteins
– DNA information is transcribed into RNA, a
single-stranded nucleic acid
– RNA is then translated into the primary structure
of proteins
more later