Download Base –sugar

Genetic Disorders
Dr: Shoroq AL-Temimi
Nucleic acid structure(N.C)
They are classified into two types:
1-Deoxyribonucleic acid or (DNA) which contains deoxyribose sugar).
2-Ribonucleic acid or (RNA) which contains ribose sugar).
Each one consist of :
Base –sugar- phosphate
Base consist of
purine
pyrimidine
Purine consist of
Adenin (A)
Guanin (G)
Pyrimidine consist of
Thyamin (T)(thyamin present in DNA while uracil
present in RNA)
Cytosine (C)
Each unit of suger-phosphate-base called nucleotide .
Molecule of DNA is composed of two nucleotide chain (2 strand) which are coiled
clockwise around one another to form double helix and held together with
hydrogen bound between A and T (T=A) ,C and G(G=C) .The DNA chains are
complementary .
RNA
1-Like DNA, RNA is a polymer of nucleotides .
2-The nucleotide in RNA, however, contain the sugar ribose & the bases Adenine
(A),Guanine (G), Cytosine (C)& Uracil (U) .
3-In other words, the bases Uracil replace the Thymine found in DNA.
4-Finally, RNA is single stranded and does not form a double helix in the same
manner as DNA.
There are three major classes of RNA :
1-Messenger RNA(mRNA):
Takes a message from DNA in the nucleus to the ribosomes in the cytoplasm.
2-Ribosomal RNA(rRNA):
Along with proteins, makes up the ribosomes, where proteins are synthesized.
3-Transfer RNA(tRNA):
Transfers amino acids to the ribosomes.
Chromosome
Chromo : mean coloured
Soma
: mean body
They presented in all nucleated cells containing DNA .
It composed of repeating units called nucleosomes each made up of eight histone
around which the DNA molecule is coiled forming the chromatin fiber .This fiber
also coiled and packed forming the chromatid of the chromosome .
Normal human Karyotype
In human chromosomes are mostly studied in peripheral blood lymphocyte , any
growing tissue including : bone marrow ,skin fibroblast or cells from amniotic
fluid or choronic villi .
In normal human nucleated cells contain 46 chromosomes arranged in 22
homologous pairs of autosomal chromosomes and one pair of sex chromosome
which is XX in female and XY in male .
Each chromosome is composed of two identical sister chromatids and each
chromosome has a narrow waist called centromere which divided the
chromosomes to short arm(p) and long arm(q) .
Chromosomes arranged according to :
1-length and size of chromosome.
2-position of centromere .
This arrangement called Karyotype , in which report the number of chr.
,abnormalities of chr. And sex of patients .
Position of centromere divided as:-Metacentric group: where the centromere in the middle dividing the
chromosome to equal p and q arm as chromosome 1,3,19,20 .
-Submetacenteric group : where the centromere divides the chromosome to
unequal arms as 2,4,5,6,-----and X.
-Acrocentric group : where the centromere at one end of the chromosome and the
short arm very small stalk as 13,14,15 ---- and Y .
The following terms are used :Phenotype:- describe the observable characteristics of a cell or organism or
proteins.
Genotype:-the information contained within those chromosomes or DNA.
Genotype and phenotype refer respectively to a gene and the protein or RNA it
encodes .
Proteins :- the end product of gene and the principle determinants of an organism
phenotype .They make up the enzymatic machinery ,the regulatory elements as
well as structural elements
Germ cell:- contain 23 chr. = haploid (half number )
Somatic cell :- contain 46 chr. =diploid (total number)
Codon:- A three-base sequence of DNA or RNA that specifies a single amino acid
Stop codon:-A codon that leads to the termination of a protein rather than the
addition of an amino acid. The three stop codons are UGA, UAA and UAG.
64 possible codes
3 of them are stop codons
61 possibilities for only 20 a.a.
= genetic code redundancy
Exon:-A region of a gene that codes for (i.e., encodes) a protein.
Intron:-A region of a gene that is in the intervening sequences between exons, and
that does not encodes a protein.
Epigenetic changes:-Changes in phenotype or gene expression due to mechanisms
other than changes in DNA nucleotide sequence, such as methylation of regulatory
sequences and histone modification.
Gene :- referring to a hypothetical unit of information that governs
inheritance of an individual characteristic in an organism .
A gene is that part of the DNA that codes for a polypeptide
30,000 genes (in contrast to what was previously though of about 100,000).
Gene expression consists of multiple steps that are dynamically and closely
regulated.
RNA plays important roles in regulation of gene expression.