88 Chapter 4
- Proteins are digested into amino acids. They feed into
the furnace at different stages of glycolysis and the
citric acid cycle based on their chemical structure.^ - Carbohydrates, fats, and proteins are all potential
sources of cellular energy because they can all be
broken down and their chemical energy can be
converted- into another form of chemical energy,
ATP, which runs the cell’s machinery.
6. Adenine of one chain always pairs with thymine of
the other chain. Cytosine of one chain always pairs
with guanine of the other chain. The bases are held
together by hydrogen bonds.^
7. A gene is a sequence of organic nitrogen base pairs
that codes for a polypeptide or protein.^
8. In our 46 chromosomes, there are billions of organic
base pairs that encode over 30,000 genes.
Introduction To Cellular
Reproduction
- Cellular reproduction is the process by which a single
cell duplicates itself. Mitosis is duplication of the
genetic material in the nucleus. Cytokinesis is the
duplication of the organelles in the cytoplasm.
Meiosis is a special kind of reduction division that
occurs only in the gonads.
The Structure Of The Dna Molecule
The History of the Discovery of DNA
- DNA was first discovered in 1869 by a German
chemist, Friedrich Miescher.^
- In the 1920s, P. A. Levine discovered that DNA
contained- phosphates, five-carbon sugars, and
nitrogen-containing bases.^
- A British citizen, Rosalind Franklin, discovered the he-
lical structure of DNA via X-ray crystallography studies.^
- James Watson, an American, and British Francis
Crick won the 1962 Nobel Prize for working out the
three-dimensional structure of the molecule.
The Anatomy of the DNA Molecule
- A DNA molecule is a double helical chain of
nucleotides.^
- A nucleotide is a complex combination of a
phosphate- group (PO 4 ), a five-carbon sugar
(deoxyribose),- and a nitrogen-containing base,
either- a purine or a pyrimidine.^
- A pyrimidine consists of a single ring of six atoms of
carbon and nitrogen. There are two pyrimidines in the
molecule: thymine and cytosine.^
- A purine consists of a fused double ring of nine
atoms- of carbon and nitrogen. There are two
purines- in the molecule: adenine and guanine.^
- In the chain of nucleotides, bonds form between the
phosphate group of one nucleotide and the sugar of
the next nucleotide. The base extends out from the
sugar.
The Cell Cycle- The cell cycle is the process by which a cell divides
into two and duplicates its genetic material.^ - A cell cycle is divided into three stages: interphase,
mitosis, and cytokinesis.
Interphase - Interphase is the time between divisions. It is
divided- into three substages: G 1 (growth one),
S (synthesis), and G^2 (growth two).^
2.^ The major portion of the life of the cell is spent in G^1.^ - During the S phase, the genetic material or DNA du-
plicates itself.^ - During the G 2 phase, mitochondria replicate and
the chromosomes condense and coil. Tubulin is
synthesized.
Mitosis - Mitosis, the cellular division in the nucleus, has
four stages: prophase, metaphase, anaphase, and
telophase.
Prophase - The duplicated chromosomes shorten, thicken, and
become visible as two sister chromatids held
together at a middle area called the centromere.^
2.^ The two kinetochores are found at the centromere.^ - The centrioles move to opposite poles of the cell
and form the spindle and asters in animal cells.^ - The nuclear membrane breaks down and the
nucleolus disappears.^ - The microtubules attach the kinetochores to the
spindle.
Metaphase - The sister chromatids align themselves in a circle at the
equator of the cell held in place by the microtubules-^
attached to the kinetochores of the centromere.^ - The centromere divides.