Molecular Genetics Flashcards
Define DNA
The genetic material that organisms inherit from their parents. DNA is used to carry the genetic code which is used to synthesise specific polypeptides
How is DNA, gene and chromosome related
Genes are units of inheritance that occupy specific locus on DNA molecule, short sequence of nucleotides that codes for particular polypeptide
A molecule of DNA condenses during cell division to form a compact structure called a chromosome. Each chromosome contains one long DNA molecule, usually carrying several hundred or more genes
What do nucleotides consist of
Phosphate group
Deoxyribose sugar
Nitrogenous base
(Deoxyribose sugar connected to nitrogenous base, phosphate group attached to deoxyribose sugar)
State the structure of DNA
Phosphate group of one nucleotide joins deoxyribose sugar of next nucleotide to form sugar phosphate backbone of the DNA molecule. Nitrogenous bases pair with each other using complementary base-pairing to form double stranded structure, comprising two polynucleotide strands joined in anti-parallel manner
State rules of complementary base pairing
Adenine forms double hydrogen bonds with thymine
Guanine forms triple hydrogen bonds with cytosine
Describe DNA replication
DNA replicates, following process of semi-conservative replication. Each polynucleotide strand of original DNA acts as template for synthesis of new complementary polynucleotide strand. Two strands of parent, original double helix are separated by enzymes. With assistance of other enzymes, nucleotides are bound to separated polynucleotide strands following rules of complementary base pairing. Results in formation of 2 double-stranded DNA molecules. Each molecule consisting of half of parent strand and newly synthesised daughter strand.
Define gene
A unit of inheritance with specific sequence of nucleotides as part of DNA molecule that contains the information to make a polypeptide. Polypeptide folds into protein in rough endoplasmic reticulum or cytoplasm
Use of DNA
DNA is used to carry genetic code, which is used to synthesise specific polypeptides. DNA directs RNA synthesis, and through RNA, DNA controls protein synthesis. RNA is intermediate in protein synthesis. Cells can control gene expression. Genes can be expressed or not expressed. Different cells express different genes
Define gene expression
The process in which the gene is accessed by enzyme, first to synthesise RNA then proteins and eventually to affect the phenotype of organism
Describe how information on DNA is used to synthesise polypeptides
(translation and transcription)
In nucleus, message in gene is copied into an mRNA, process known as transcription. mRNA travels to cytoplasm and attaches to ribosome. As ribosome moves along mRNA, it synthesises a polypeptide. Synthesis of polypeptide chain from mRNA is translation. When ribosome leaves mRNA, polypeptide is released
What base replaces adenine in mRNA
Uracil
What are codons
Triplets of nucleotide bases, smallest units of uniform length that can code for all the amino acids
What are similarities between DNA and RNA
Both have sugar-phosphate backbone
Both contain three common nitrogenous bases: adenine guanine and cytosine
What are differences between mRNA and DNA
no. of strands, structure, monomers, pentose sugar, nitrogenous base, ratio of bases, bonds between bases
Define mutation
A spontaneous or induced change in DNA sequence of genes, or change in number or structure of chromosomes.
Describe mutagens
Mutagens are physical or chemical agents that can cause alterations to DNA, resulting in changes in the sequence of DNA. Rate of spontaneous mutation is greatly increased with presence of mutagens. Mutagens include high energy radiation (gamma rays) or chemical mutagens (tar)
Describe genetic engineering
A technique used to transfer genes from one organism to another. Individual genes may be taken from cells of one organism and inserted into cells of another organism of same or different species using a vector. Vectors carry the genes to intended cells.
Why is bacteria used to produce insulin
It is relatively easy to transfer genes into bacterium. Bacteria contains plasmids, circular strands of DNA that replicate separately from bacterial DNA. A plasmid only has small number of genes, which may be useful to bacteria under certain conditions is not necessary for its survival. Insulin gene can be inserted easily into plasmid. Bacteria takes short time to replicate. When bacterium replicates, plasmid also replicated, single cell reproduces through repeated cell divisions to form clones of itself, bacteria transcribe and translate insulin gene in plasmid to produce large quantities of insulin
Describe obtaining of DNA segment for insertion
Obtain DNA segment in human chromosome containing insulin gene. Cut out gene using restriction enzyme. Enzyme cuts two ends of gene to produce “sticky ends”. Each “sticky end” is single strand sequence of DNA bases. Bases pair with complementary bases to form a double strand
Describe replication of obtained insulin gene in bacterium
Obtain plasmid from bacterium. Cut open plasmid with same restriction enzyme, produces “sticky ends” complementary to ends of insulin gene. Mix the plasmid with DNA fragment containing insulin gene. DNA fragment containing human insulin gene will bind to plasmid by complementary base pairing between “sticky ends”, add DNA ligase to seal DNA fragment to plasmid, plasmid is recombinant plasmid. Mix plasmid with E. coli bacterium, apply temporary heat or electric shock, opens cell membrane for plasmid to enter. Transgenic bacterium with insulin gene will be isolated and grown on large scale under optimum conditions. Transgenic bacterium synthesises insulin together with other proteins from plasmid. Insulin must be extracted and purified before use.
Describe some benefits of genetic engineering
Low-cost production of medicines
Production of crops that grow in extreme conditions
Development of pesticide and pest resistant crops
Development of food designed to meet specific nutritional goals
What are some social issues behind genetic engineering
Some biotechnology companies engineered crops such that plants produce seeds that cannot germinate. Technology such as gene therapy may lead to class distinctions. People with sufficient financial means can benefit from technology. Some people feels it is morally wrong to exploit animals for research.
