University:
Lehman College
Course:
BIO 410 | Cell Physiology and Biochemistry
Academic year:

2023
Views:

353

Pages:

3
Author:

Finnegan Le

Structure of DNA DNA is double-stranded complex nucleic acid. It is formed by deoxyribose, phosphoric acid, and four types of bases. Each DNA molecule consists of two polynucleotide chains which are twisted around one another in the form of a double helix. The two chains are formed by deoxyribose sugar and phosphate. Deoxyribose sugar and phosphate form the backbone of the DNA molecule. Each chain of DNA molecule consists of many nucleotides. Each nucleotide is formed by: Deoxyribose sugar Phosphate Nitrogenous Base: Purine: Adenine (A), Guanine (G) Pyrimidine: Thymine (T), Cytosine (C) Adenine of one strand binds with thymine of the opposite strand. Similarly, cytosine of one strand binds with guanine of the other strand. The hereditary information that is encoded in DNA is called the genome. Each DNA molecule is divided into discrete units called genes Gene Gene is a portion of DNA molecule that contains the code for the synthesis of a specific protein from amino acid. Gene is the basic hereditary unit of the cell. In the nucleotide of DNA, three successive base pairs are together called a triplet or codon. Each codon codes for one amino acid. There are 20 amino acids and there is a separate code for each amino acid. Example: CCA code for glycine, GGC code for proline. Each gene forms the code word for a particular protein to be synthesized in ribosome from amino acids. Genetic Disorders Genetic disorders are hereditary disorders due to defects in genes. Causes of Gene Disorders: Genetic variation: Presence of a different form of a gene. Genetic mutation: Change of DNA sequence within a gene or chromosome of an organism. Classification of Genetic Disorders Genetic disorders are classified into four types: Single gene disorders/Mendelian disorders: Occurs due to variation or mutation in one single gene. Examples: Sickle cell anemia and Huntington's disease. Multifactorial genetic disorders/polygenic disorders: Caused by a combination of environmental factors and mutations in multiple genes. Examples: Coronary heart disease, Alzheimer's disease, arthritis, and diabetes. Chromosomal Disorders Chromosomal disorder is a genetic disorder caused by abnormalities in chromosomes. Chromosomal disorder is classified into two types: Structural abnormality: Alteration of chromosome structure. Example: Malignancies Numerical abnormality: Monosomy: Absence of one chromosome. Example: Turner's Syndrome Trisomy: Presence of one extra chromosome. Example: Down syndrome Mitochondrial DNA Disorders Caused by the mutation in the DNA of mitochondria. Example: Kearns-Sayre Syndrome (neuromuscular disorder), Leber's hereditary optic neuropathy. Ribonucleic Acid (RNA) Ribonucleic acid (RNA) is a nucleic acid that contains a long chain of nucleotide units. It is similar to DNA but contains ribose instead of deoxyribose. Various functions coded in the genes are carried out in the cytoplasm of the cell by RNA. RNA is formed from DNA. Structure of RNA Each nucleotide of RNA is formed by: Ribose - sugar Phosphate Nitrogenous bases Purine: Adenine (A), Guanine (G) Pyrimidine: Uracil (U), Cytosine (C) Uracil replaces the thymine of DNA. Similar structure of thymine.