UNIT 3: Molecular Genetics
Chapter 6: DNA: Hereditary Molecules of Life pg. 268 All cells, such as: animal, plant, fungus, protests, archaea, and bacteria use
molecules of deoxyribonucleic acid (DNA) to carry information. Parent cells
produce daughters (mitosis) that have an exact copy of the parents DNA.
How doe the cell replicate it s DNA, an exact copy without errors or being
altered in any way. Alter DNA is called a mutation, and the cells in which
this occurs does not function properly. DNA has repair mechanisms to
minimize any errors.
The process of DNA replication is known as semi-conservative replication,
where each new DNA double strand is made up of an old and newly
replicated strand. This process ensures that an exact copy is created.
6.1: The Molecular Basis of Inheritance
pg. 270 - 272
DNA is responsible for maintaining genetic continuity of the species, and
therefore the continuity of life. DNA contains the information of life, the
production of proteins, the function and construction of cells.
During reproduction, sexual or asexual, DNA must be replicated and passed
on from one generation to the next. The information is stored in the nucleus
of each cell and can be found in chromosomes, must be copied and passed
on to the next generation of cells, through a process of mitosis or meiosis.
The structure of the DNA molecule consists of many nucleotides. A
nucleotide consists of three parts, phosphate group, deoxyribose sugar group,
and one of four nitrogen bases (adenine, thymine, guanine, and cytosine).
DNA is responsible for coding for the production of proteins. The genes
found on each chromosome are coded information for the production of each
protein produced. The production of proteins is a three step process,
transcription, translation, and protein synthesis.
Heredity and DNA
All new cells come from pre-existing cells (Cell Theory). The DNA from
the pre-existing cell must be copied and passed onto the new daughter
cells.
DNA is used to build proteins and new cells.
Genes and Chromosomes
Mendel, the father of genetics, determined that factors, later called genes,
determined the genotype and phenotype of organisms. During reproduction,
these factors were inherited by offspring, passed on from generation to
generation.
The genes are the coded regions of DNA, responsible for the production of
proteins. Mendel determined that there are two genes for each trait, however
it is now understood that there maybe several versions of alleles for each
trait.
Genes are located long the DNA molecule, coded regions (exons) and noncoded regions (introns) giving rise to different lengths of DNA strands.
Within the same species of organism the gene for a particular trait is located
in the same position and chromosome for all.
The DNA molecule contains a large amount of information, the molecules if
laid out length wise could not fit within the nucleus, therefore the DNA
molecule must be super-coiled to fit. The DNA molecule is wrapped around
a special protein called a histone.
Histone – is a special protein molecule that is the core around which the
DNA strand wraps.
DNA molecules are wrapped around a number of histones forming
complexes, which are bundled into chromatin fibres.
Prokaryotic DNA is different then eukaryotic, that it is simpler, and found in
the cytosol of the cell. Bacterial DNA is found in loops. Smaller accessory
loops of genetic material are called a Plasmid. Plasmids can be copied and
passed from bacteria to another.
Plasmid – is a small circular section of DNA found in the Cytosol of
bacteria; replicates independently of the chromosomal DNA.
Figure 2: Genes make up the coding section of DNA. DNA strands are tightly coiled and compacted to
form chromosomes, which are visible during cell division.
The Genome
The complete set of genetic information found in an organism is called the
genome. In eukaryotic organisms (diploid) this information is located in
many chromosomes. In the nucleus there is two sets of each chromosome,
these pairs are called homologous pairs. They are the same in length,
centromere location, and gene loci, although they may have different alleles
for a particular trait.
For humans there are 23 pairs of chromosomes. The 23 chromosome is
known as the sex chromosome. There are approximately 20,000 genes, made
up of more then 3 billion base pairs.
Genome – is the complete set of an organism’s hereditary information.
Figure 3: Micrograph of the Human Genome