chapter 20: molecular genetics Flashcards
what is DNA?
- deoxyribonucleic acid is a molecule that carries genetic information
> the information is important for all cellular functions
How is DNA organised inside your cells?
- a small segment of DNA carries a gene that stores information used to make a single polypeptide
> polypeptides are used to make proteins
> proteins are responsible to determining the characteristics of an organism - each DNA molecule consists of two strands twisted around each other to form a double helix
> a helix is a coiled structure like a corkscrew or a spring - a molecule of DNA is wrapped around proteins to form a single chromatin thread
- during cell division, chromatin threads coil tightly into structures called chromosomes inside the cell nucleus
what are the basic units of DNA?
-the basic unit of DNA is called nucleotide
each nucleotide is made of
- a sugar called DEOXYRIBOSE
- a phosphate group
- a nitrogen-containing base
- there are four types of nitrogen containing bases in DNA
> adenine (A), cytosine (C), guanine (G), and thymine (T)
what happens when you put nucleotides together? and what is a DNA molecule made up of?
there are four different nucleotides:
- adenine nucleotide
- cytosine nucleotide
- guanine nucleotide
- thymine nucleotide
> nucleotides can be joined together to form long chains called polynucleotides
- each gene is made of a sequence of nucleotides
the sequence of nucleotides (Bases) can very
many different genes
- a DNA molecule is made up of two anti-parallel polynucleotide chains
> they are anti-parallel because the two chains run in opposite directions
>the bases of one chain are bonded to those of the opposite chain according to the rule base pairing
what is rule of base pairing?
- adenine (A) always bonds with thymine (T)
> adenine and thymine are called complementary bases - cytosine (C) always bonds with guanine (G)
> cytosine and guanine are called complementary bases
> complementary bases are joined together by hydrogen bonds
what are genes?
- DNA molecule may carry many genes along its length
> genes are the basic units of inheritance in a living organism
> a gene is a sequence of DNA nucleotides that controls the formation of a single polypeptide which can be used to make proteins
> each gene stores a message that determines how a protein should be made in a cell
> the message is stored by a gene known as the genetic code
what is the structure of a gene?
- each gene consists of two polynucleotide chains
- one of the chains determine the type of protein made
> the TEMPLATE - the template contains a sequence of nucleotides or bases
> the sequence stores information as follows: three bases code for one amino acid
> triple code or codon
-eg. if the template has 10 triple codes, the template will enable the cell to make a polypeptide containing ten amino acids
how are polypeptides or proteins made?
- polypeptides are made through two-step process
> transcription and translation
> transcription occurs in the nucleus and translation occurs in the cytoplasm - transcription: the process by which the DNA template is used to make a single-stranded molecule called
>messenger RNA (mRNA)
> mRNA has a base sequence complementary to that of the DNA template - it carries the message from the DNA codons out of the nucleus to the cytoplasm, where the protein is synthesise
- RNA contains Uracil (U) instead of thymine
- translation: is the process by which the sequence of mRNA codons is used to make a polypeptide
what is genetic engineering?
- it is a technique used to transfer genes from one organism to another
> individual genes may be cut off from the cells of one organism and inserted into the cells of another organism of the same or different species
> the transferred gene can express itself in the recipient organism - a vector is required for the transfer of genes
> vector can be another DNA molecule, a bacterium or a virus used to carry the genes of one organism to another
> small circular DNA called plasmids, obtained from bacteria can be used to transfer genes
what are the advantaged of transferring human insulin gene into bacteria?
- does not induce allergic response in the patient
> insulin produced is identical to human insulin - it is easier and cheaper to produce insulin in large quantities
- less risk of contamination by disease-causing microorganisms
> compared to insulin obtained from the pancreases of animals - ethical concerns of vegetarians or religious groups can be overcome
describe the steps of transferring a human insulin gene to a bacterium.
- obtain a fragment of DNA in human chromosome that contains the insulin gene
> cut the gene using a RESTRICTION ENZYME
> an enzyme which cuts the restriction site at the two ends of the gene to produce ‘sticky ends’
- each ‘sticky end’ is a single strand sequence of DNA bases
> these bases can pair with complementary bases to form a double strand - obtain a plasmid from a bacterium and cut the plasmid with the same restriction enzyme
> produces ‘sticky ends’ which are complementary to the ends of the insulin gene - mix the plasmid with the DNA fragment containing the human insulin gene
> the human insulin gene will bind to the plasmid by complementary base pairing between the ‘sticky ends’
- add the enzyme DNA ligase to seal the human insulin gene to the plasmid
> plasmid containing DNA from two different organisms is called RECOMBINANT PLASMID - mix the recombinant plasmid with E. coli bacterium
> apply temporary heat and electric shock
- this opens up pores in the cell surface membrane of the bacterium for the plasmid to enter - this TRANSGENIC BACTERIUM will use the new gene to make insulin
> such bacteria can be isolated and grown for mass production of human insulin
> the insulin has to be extracted and purified before it can be used
describe the transfer of a pest-resistant gene from a bacterium to a crop plant.
- use restriction enzyme to cut out the gene from the bacterial DNA to produce sticky ends
- use the same restriction enzyme to cut the plasmid to produce complementary sticky ends
- insert the gene into the plasmid
- insert the recombinant plasmid into the bacterium
- allow this bacterium to infect plant cells
- induce the plant cells to produce recombinant plants
> a plant that has acquired a foreign gene is a transgenic plant
what are the advantages of growing pest-resistant plants?
- food production will be increased
- may reduce environmental pollution as less pesticides are used
what are the disadvantages of growing pest resistant plants?
- insect pests may develop resistance to the poison produced by the plant
- pest resistance may be spread to weeds through cross pollination
- useful insects may be killed
- producing herbicide resistant crops may lead to more effective destruction of weeds + killing of insects
> ecological imbalance
compare selective breeding to genetic engineering.
SB: plants and animals used for breeding must be closely related or belong to the same species
GE: genes from any plants or animals can be inserted into non-related species or different species
SB: defective genes may be transmitted along with the healthy genes to the offspring
GE: genes are carefully selected before transfer into an organism
> reduces the risk of genetic defects being passed on to the offspring
SB: selective breeding is a slow process
> involves breeding over several generations
GE: uses individual cells which reproduce rapidly in the laboratory
SB: less efficient
GE: more efficient
