DNA & genetics IEB & DBE Life Sciences grade 12 notes
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Module
Life Sciences
Institution
12th Grade
This set of notes contain a detailed explanations on DNA & genetics containing the following:
Cell nucleus
DNA - the code of life and RNA
Structure & location of DNA & RNA in a cell
Replication of DNA
The polymerase chain reaction (PCR)
Human genome
Protein synthesis
Genetic aberrations...
, DNA, Genetics & Genetic engineering
Cell nucleus
Nucleus enclosed in double nuclear membrane/nuclear envelope (continuous with endoplasmic
reticulum), contains special cytoplasm called nucleoplasm (contains free nucleotide bases)
Nuclear membrane has small pores (nuclear pore), nucleoplasm in contact with ordinary cytoplasm
Dark round body seen in nucleus, nucleolus (plural: nucleoli).
Nucleolus manufactures & contains ribosomal RNA (rRNA- ribose nucleic acid, part of ribosomes)
In nucleus is network of fine threads, called chromatin network
Constituent (component) of chromatin is special chemical called nuclear DNA (Deoxyribose
Nucleic Acid). When cell about to divide, DNA molecules coil up tightly. Makes them much fatter &
shorter. In coiled up condition call them chromosomes. Nuclear DNA has two important functions:
1. Controls synthesis (manufacture) of proteins (fight infections, build enzymes, build muscles
& help nerve functioning).
2. Carries hereditary characteristics from parents to offspring. Small amounts of DNA found
within chloroplasts (chloroplastic DNA) & mitochondria (mitochondrial DNA/mtDNA).
Chloroplastic DNA & mtDNA control protein synthesis within these organelles themselves.
Mitochondrial DNA, help trace ancestors. DNA occurs outside nucleus, extranuclear DNA.
Nucleus functions
Regulates metabolism of cell. Regulates changes, occur in cell when
substances are built up (anabolic process)/broken down (catabolic process).
Regulates structure of cell, controls types of substances synthesized in cell.
Carries hereditary characteristics of cell. As cell divides, hereditary
characteristics in nucleus of mother cell passed on to daughter cells.
Control centre of cellular operations/activities.
DNA - the code of life and RNA
DNA structure and coding
, Discovery of DNA
1950’s, scientists had found out that DNA consisted of molecules of deoxyribose sugar,
phosphate molecules and four nitrogen bases: adenine, thymine, cytosine and guanine.
1953, X-ray crystallography (Diffraction images of DNA), Maurice Wilkins, & Rosalind
Franklin, show double helix structure. Maurice Wilkins disliked Rosalind Franklin. Showed
X-ray diffraction to James Watson. Watson teamed up with Francis Crick
In 1953 Watson & Crick put forward model of DNA, double-helix w/complementary
base-pairs. (unravelled the genetic code)
1960's (mechanism of protein synthesis) - Vernon Ingram & Sydney Brenner. How
amino acids strung together in polypeptide chains to form proteins.
1962 James Watson, Francis Crick & Maurice Wilkins awarded Nobel prize.
Nucleic acid
DNA & RNA are nucleic acids, made of smaller units or monomers called nucleotides.
Each nucleotide made of: A nitrogenous base: nitrogenous base of one nucleotide, linked by
weak hydrogen bonds (DNA only).
A sugar portion (deoxyribose: DNA; ribose: RNA)
A phosphate portion
Mononucleotides/monomers (1 nucleotide), Dinucleotides (2 nucleotides) &
Polynucleotides/polymers (many nucleotides bonded together)
Two different groups of nucleotides, namely those with nitrogenous base formed:
PYRIMIDINES (small) i.e. Cytosine, Thymine (only DNA) & Uracil (only in RNA)
PURINES (big) i.e. Adenine and Guanine (in both DNA & RNA)
Structure & location of DNA & RNA in a cell
Location of DNA
Nucleus has chromatin network (unwinds during cell division). Most DNA found in
chromosomes. This nuclear DNA. Small amounts also found inside organelles, mitochondria
(mitochondrial DNA or mtDNA) & chloroplast (chloroplastic DNA).
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