140
UNIT ONE
b. DNA molecules are replicated during interphase of
the cell cycle.
c. Each new DNA molecule consists of one old strand
and one new strand.
3. Genetic code
a. Some of the sequence of nucleotides in a DNA
molecule represents the sequence of amino acids
in a protein molecule. This correspondence is the
genetic code.
b. RNA molecules transfer genetic information from
the nucleus to the cytoplasm.
c. RNA synthesis is transcription. Protein synthesis is
translation.
4. RNA molecules
a. RNA molecules are usually single-stranded, have
ribose instead of deoxyribose, and uracil in place
of thymine.
b. Messenger RNA molecules, synthesized in the
nucleus, have a nucleotide sequence complementary
to that of an exposed strand of DNA.
c. Messenger RNA molecules move into the
cytoplasm, associate with ribosomes, and are
templates for the synthesis of protein molecules.
5. Protein synthesis
a. Molecules of tRNA position amino acids along a
strand of mRNA.
b. A ribosome binds to an mRNA and allows a tRNA
to recognize its correct position on the mRNA.
c. The ribosome has enzymes required for the
synthesis of the protein and holds the protein until
it is completed.
d. As the protein forms, it folds into a unique shape.
e. ATP provides the energy for protein synthesis.
4.7
CHANGES IN GENETIC INFORMATION
(PAGE 135)
A DNA molecule contains a great amount of information.
Mutation changes the genetic information. Not all
changes to DNA are harmful.
1. Nature of mutations
a. Mutations are rare and alter health or appearance.
b. Single nucleotide polymorphisms are more
common and have no observable effect.
c. A protein synthesized from an altered DNA
sequence may or may not function normally.
d. Mutations may be spontaneous or induced.
e. DNA changes are transmitted when the cell divides.
2. Protection against mutation
a. Repair enzymes can correct some forms of DNA
damage.
b. The genetic code protects against some mutations.
c. A mutation in a sex cell, fertilized egg, or embryo
may have more effects than a later mutation because
a greater proportion of cells bear the mutation.
3. Inborn errors of metabolism
a. An enzyme deF
ciency may cause an inborn error
of metabolism, in which a metabolic pathway is
blocked.
b. The substrate builds up and the product
diminishes.
4.5
CELLULAR RESPIRATION (PAGE 120)
Cellular respiration transfers energy from molecules such
as glucose and makes it available for cellular use. This
process occurs in three distinct, interconnected series of
reactions.
1. Glycolysis
a. Glycolysis, the F
rst step of glucose catabolism,
occurs in the cytosol and does not require oxygen.
b. Glycolysis can be divided into three stages, in
which some of the energy released is transferred to
ATP.
c. Some of the energy released in glycolysis is in the
form of high-energy electrons attached to hydrogen
carriers.
2. Anaerobic reactions (absence of oxygen)
a. Oxygen is the F
nal electron acceptor in the aerobic
reactions of cellular respiration.
b. In the anaerobic reactions, NADH and H
+
instead
donate electrons and hydrogens to pyruvic acid,
generating lactic acid.
c. Lactic acid builds up, eventually inhibiting
glycolysis and ATP formation.
d. When oxygen returns, in liver cells lactic acid
reacts to form pyruvic acid.
3. Aerobic reactions (presence of oxygen)
a. The second phase of glucose catabolism occurs in
the mitochondria and requires oxygen.
b. These reactions include the citric acid cycle and
the electron transport chain.
c. Considerably more energy is transferred to ATP
during the aerobic reactions than during glycolysis.
d. The products of the aerobic reactions of cellular
respiration are heat, carbon dioxide, water, and
energy.
e. The citric acid cycle decomposes molecules,
releases carbon dioxide, releases hydrogen atoms
that have high-energy electrons, and forms ATP.
f. High-energy electrons from hydrogen atoms enter
an electron transport chain. Energy released from
the chain is used to form ATP.
g. Each metabolized glucose molecule yields up to
thirty-eight ATP molecules.
h. Excess carbohydrates may enter anabolic pathways
and be polymerized into and stored as glycogen or
react to produce fat.
4.6
NUCLEIC ACIDS AND PROTEIN
SYNTHESIS (PAGE 124)
DNA molecules contain and maintain information that
tells a cell how to synthesize proteins, including enzymes.
1. Genetic information
a. DNA information speciF
es inherited traits.
b. A gene is a portion of a DNA molecule that
includes, in its nucleotide base sequence, the
genetic information for making a protein.
c. The DNA nucleotides from both strands pair in a
complementary fashion, joining the two strands. A
binds T, and G binds C.
2. DNA replication
a. Each new cell requires a copy of the original cell’s
genetic information.
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