Genes & Genetic Engineering - Revision World

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12 Δεκ 2012 (πριν από 4 χρόνια και 9 μήνες)

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Genes & Genetic Engineering

Contents


Genetic Code


Cell Cycle


Sexual Reproduction


Applications of Gene Technology

Genetic Code


Sequence of bases on DNA


These code the sequence of amino acids in proteins



20 amino acids


4 bases




Universal Code
: The code is used between species. Each
base sequence codes for the same amino acid


Many base sequences can code for the same amino acid


“Stop” (UAG, UGA, UUA) does not code for an amino acid

grouped into 3s


64 combinations

Codon


Genetic code

1
st

2 are most important

Genetic Code

Amino Acid mRNA Codons

Cell Cycle


Cell cycle varies from hours to years


-

Bacterial cells divide every 30 minutes


-

Liver cells divide every 2 hours



Four cycles:


-

Gap 1, Synthesis, Gap 2, Mitosis



Mitosis has four phases:


-

prophase, metaphase, anaphase, telophase



Mitosis results in 2 daughter cells, genetically identical to
each other. Used for growth and asexual reproduction

Cell Cycle

mitosis

Gap 1

Gap 0

DNA synthesis

Gap 2

Cell size increases

RNA and synthesise
proteins produced.

Preparations for DNA
synthesis.

Cell stops dividing.

Temporary or permanent.

DNA synthesis
(replication).

Cell grows & produces
proteins for cell division.
Determines if cell can
undergo mitosis.

Interphase:

Gap 1 + synthesis + Gap 2

Meiosis (Sexual Reproduction)


Mitosis produces 2 genetically identical daughter cells


Meiosis occurs directly afterwards with 2 further divisions


Meiosis therefore results in 4 daughter cells with:


-

half the number of chromosomes (diploid 2n


haploid n)


-

new combinations of genes so no two will be identical



Meiosis (Sexual Reproduction)


Advantages
:


-

genetic variation and wide diversity of life


-

allows species to adapt and evolve




Disadvantages
:


-

complex


-

slower than mitosis

Applications of Gene Technology


3 main applications to date:



-

Gene Products: using genetically modified (GM)
organisms (usually microbes) to produce chemicals for
medical or industrial applications



-

New Phenotypes: using gene technology to alter the
characteristics of organisms such as crops



-

Gene Therapy: using gene technology on humans to
treat diseases

Gene Products

Bacteria

Manufacture of cheese

Rennin

Yeast

Hep B antigen

Vaccines

Fungi

Antibiotic to kill bacteria

Penicillin

Bacteria

Human growth hormone

HGH

Bacteria

Human blood clotting
(haemophiliacs)

Factor VIII

Bacteria

Increase cows’ milk yields

BST

Goats

Anti
-
blood clotting
(surgery)

Anti
-
thrombin

Sheep

Cystic fibrosis

AAT

Host Organism

Application

GM Product

New Phenotypes


These include:


-

Fast
-
growing sheep & fish


-

Crops resistant to insects, herbicides & viruses


-

Long life tomatoes & some fruit


-

Crop improvement & nitrogen
-
fixing crops


-

Cattle resistant to mastisis (


higher yield of milk)


-

Sheep resistant to ticks (


may not need sheep dip)

Gene Therapy


Altering the genotype of a tissue or organ



In early stages but treatments hope to include:


-

GM white blood cells that produce proteins that kill
cancer cells


-

targeting genes at cancer cells to kill them or revert
them back to normal cells


-

white blood cells that would not reproduce if infected
with HIV


-

germ
-
line modification (only present in animals) which
is currently illegal


-

at present, only somatic cell therapy is legal which
alters only specific cells in the body

Summary


Genetic code: Sequence of 20 amino acids & 4 bases,
grouped into 3s. It is a universal code (all species)



Cell cycle: Interphase = Gap 1 + synthesis + Gap 2



Sexual reproduction, meiosis produces non
-
identical
daughter cells and is vital for organisms to evolve



Applications of gene technology include gene products (e.g.
penicillin), new phenotypes (long life tomatoes) and gene
therapy (in early stages)