GENETICS
•The branch of biology that deals with heredity, especially the mechanisms of hereditary transmission and the variation of inherited characteristics among similar or related organisms
GENE AND ALLELE
•Biological unit of heredity
•Gene hold the information to build and maintain their cells and pass genetic traits to offspring’s
•In cells, a gene is portion of DNA
•ALLELE Is one member of a pair or series of different forms of a gene. Homozygous-have same alleles. Heterozygous-different alleles of the gene
CHROMOSOME
•Chromosomes—DNA, RNA & proteins that make up chromosme
•Chromatids: one of the two identical parts of the chromosome.
•Centromere: the point where two chromatids attach 46 chromosomes.
•22 pairs Autosomes and 1 pair Sex chromosomes
NUCLEOTIDE
•Group of molecules that are linked together to form the building blocks of DNA and RNA
•Composed of phosphate group, the bases: adenosine, cytosine, guanine and thymine and a pentose sugar.
•In case of RNA, thymine base is replaced by uracil.
•CODON : series of three adjacent bases in one polynucleotide chain of a DNA or RNA molecule which codes for a specific amino acid.
•Anucleosideconsists of a nitrogenous base covalently attached to a sugar (ribose or deoxyribose) but without the phosphate group.
•A nucleotideconsists of a nitrogenous base, a sugar (ribose or deoxyribose) and one to three phosphate groups.
GENETIC CODE
•Sequence of nucleotides in a DNA or RNA molecule that determines the amino acid sequence in the synthesis of proteins.
•Importance of DNA lies in its ability to control the formation of proteins in the cell, which it achieves by means of a genetic code.
•Consists of successive “triplets” of bases—that is, each three successive bases is a code word.
•Successive triplets eventually control the sequence of amino acids in a protein molecule that is to be synthesized in the cell.
•DNA has two functions.
•Self-renewing data repository that maintains a constant source of genetic information for the cell.
•Serve as a template for the translation of genetic information into proteins, which are the functional units of the cell.
STEPS OF PROTEIN SYNTHESIS
1.Transcription
2.Translation
3.Post translational modifications
Transcription
•Synthesis of RNA from a DNA template, mediated by an enzyme called RNA polymerase in the Nucleus
•Requirements:
•DNA template
•RNA polymerase
•Activated ribonucleotides
•The code that is present in the DNA strand is eventually transmitted in complementary form to the RNA chain.
•The ribose nucleotide bases always combine with the deoxyribose bases in a fixed combination.
DNA BaseRNA Base
Guanine…………………………….……Cytosine
Cytosine ………………………..…….… Guanine
Adenine …………………………………… Uracil
Thymine ………………………………… Adenine
•The RNA that is initially transcribed from a gene is called the primary transcript.
•Most eukaryotic genes contain exons, DNA sequences that are present in the mature mRNA, alternating with introns, which are not present in the mRNA
Types of RNA
•mRNA
•tRNA
•rRNA
•miRNA
TYPES OF RNA
•mRNAmolecules are long, single RNA strands that are suspended in the cytoplasm. They contain codons that are exactly complementary to the code triplets of the DNA genes.
•tRNA—Carrier for specific amino acids from cytoplasm to mRNA. Has sites for binding amino acid & mRNA
•rRNA—Functions in association with tRNA& mRNA. Present in ribosomes
•miRNA—Non-coding RNA. Regulate gene expression
Translation
•Translation is the synthesis of protein from RNA inside the Ribosomes
•Requirements: Amino acids, mRNA, tRNAand ATP
•Begins at AUG
•Ends at UAG, UAA, UGA
•It is common to have more than one ribosome on a given mRNA chain at a time.
•The mRNA chain plus its collection of ribosomes is visible under the electron microscope as an aggregation of ribosomes called a polyribosome.
TRANSLATION
Peptide bonds formed between successive amino acids
Process stops at chain termination codon
Release of polypeptide
POST-TRANSLATIONAL MODIFICATIONS
•Folding
•Hydroxylation
•Carboxylation
•Glycosylation
•Phosphorylation
•Cleavage of peptide bonds
CELL DIFFERENTIATION
•Special characteristic of cell growth and cell division is cell differentiation, which refers to changes in physical and functional properties of cells as they proliferate in the embryo to form the different bodily structures and organs.
APOPTOSIS
•When cells are no longer needed or become a threat to the organism, they undergo a suicidal programmed cell death, or apoptosis.
•Process involves a specific proteolytic cascade that causes the cell to shrink and condense, disassemble its cytoskeleton, and alter its cell surface so that a macrophage, can attach to the cell membrane and digest the cell.
•Orderly cell death that results in disassembly and phagocytosis of the cell prior to leakage of its contents so that neighboring cells usually remain healthy.
•Initiated by activation of a family of proteases called caspases, stored in the cell as inactive procaspases.
•Daily tissues are being remodeled during development, balances by the formation of new cells in healthy adults.
•Abnormalities of apoptosis results in neurodegenerative diseases such as Alzheimer disease, as well as in cancer and autoimmune disorders.
•Some drugs have been used successfully for chemotherapy appear to induce apoptosis in cancer cells.
NECROSIS
•Cells that die as a result of an acute injury usually swell and burst due to loss of cell membrane integrity, a process called cell necrosis.
•Necrotic cells may spill their contents, causing inflammation and injury to neighboring cells.
CANCER
•Cancer is caused in most instances by mutation or by some other abnormal activation of cellular genes that control cell growth and cell mitosis.
•Proto-oncogenes are normal genes that code for various proteins that control cell adhesion, growth, and vision.
•If mutated or excessively activated, capable of causing cancer
•Antioncogenes(tumor suppressor genes) suppresses the activation of specific oncogenes.
•Loss or inactivation of antioncogenescan allow activation of oncogenes that lead to Cancer
•Minute fraction of the cells that mutate in the body ever lead to cancer.
1.Most mutated cells have less survival capability than normal cells
2.Few of the mutated cells that survive become cancerous, because even most mutated cells still have normal feedback controls that prevent excessive growth.
3.Cells that are potentially cancerous are destroyed by the body’s immune system
Why mutation occurs?
•precision with which DNA chromosomal strands are replicated in each cell before mitosis can take place, along with the proofreading process that cuts and repairs any abnormal DNA strand before the mitotic process is allowed to proceed
•Despite these precautions, probably one newly formed cell in every few million still has significant mutant characteristics.
Causes of mutation
•Drugs/chemical substances
•Ionizing radiation
•Hereditary tendency
•Viruses
•Physical irritants
•Cancer cells lack normal growth factors that lead to uncontrolled growth usually.
•Less adhesive so become part of circulation
•Angiogenicfactor—provision of adequate nutrition
•Cancer cell kills other cells due to competition for nutrients