DNA Structure: Genes, Chromosomes, Replication, Mitosis and Meiosis

DNA Structure 1
DNA Structure 3
DNA Structure
By
Course
Lecturer
University
Department
Date

DNA Structure 2
1.1: Structures of DNA, genes and chromosomes
DNA STRUCTURE
According to Saenger (2013) deoxyribonucleic acid is composed of nucleotide
molecules. Each nucleotide molecule contains a sugar group, nitrogen base and phosphate
group. Nitrogen bases include cytosine (C), guanine (G), adenine (A) and thymine (T). The
order of the bases determines genetic code or deoxyribonucleic acid instructions. The human
DNA has about 3 billion bases.
The sequence of DNA creates genes which tell how to make proteins. Molecules of
DNA are long in such that they cannot fit in cells with no proper packing. It contains
organism instructions needed to reproduce, live and develop. Nucleotides attached to create
two spiral strands to form a double helix structure (Saenger 2013).
GENE STRUCTURE
A gene is a section of deoxyribonucleic acid composed of amino acid information
coding for a polypeptide chain and other regulatory sequences that are important for
appropriate expression Hay (2013). A gene is a DNA sequence that is significant for the
manufacture of functional produce (RNA molecule or polypeptide). Genes are discontinuous
in human (eukaryotic genomes). Not all genes are active in cells which show that not all are
expressed.
According to Hay (2013), there are two types of genes: multigene families and
operons. It indicates that cells acquire specialised functions (differentiated). Gene's
expression regulates promoter regions. There are regulatory elements which include silencers,
locus control regions and enhancers. Both regulatory elements and promoters are sites of
genetic disease mutation which alter with regular gene expression. Genes are set along the
chromosomes. Genes have a definite, specific position called gene locus.

DNA Structure 3
According to Hay (2013),
CHROMOSOMES STRUCTURE
Therman and Susman (2012) suggested that chromosomes are a thread like structure
in which the DNA is packaged. They are made of histone (tightly coiled DNA coiled many
times around proteins) that supports the chromosome structure. They are not visible under a
microscope, not even in cell’s nucleus. The position of the centromere on the given
chromosome describes the location of specific genes and provides the chromosome with its
characteristic shapes.
In all stages of an organism’s life, DNA is more organized and structure in eukaryotes
Therman and Susman (2012). Human have 23 chromosomes number for a total number of
46.homologous chromosomes also known as pairs of chromosomes have similar genes
although there are differences between the gene versions on the couple.
According to Therman and Susman (2012)
1.2: DNA REPLICATION
DNA replication process produces two similar replicas of DNA from an original one
(Méchali 2010). It involves three main steps which are: initiation, elongation and termination.
The DNA strands are separated during replication, where each original DNA molecule strand
acts as a pattern for the creation of its complement (semiconservative replication). The end