14 — molecular genetics Flashcards
Describe the relationships between gene, DNA and chromosomes. [4]
Gene is a sequence/ segment of DNA [1] codes for the formation of a specific polypeptide. [1]
Many genes made up a DNA. [1]
Chromosome is the condensed structure of DNA wrapped around proteins (histones) visible only during cell division. [1]
Describe the structure and function of DNA. [6]
DNA is a double helix structure [1], made up of two polynucleotide chains twisted around each other. [1] The two polynucleotide chains are held together by hydrogen bonding between complementary nitrogenous bases [1], adenine pairs with thymine and cytosine pairs with guanine. [1]
Each polynucleotide chain is made up many nucleotides and each nucleotide is made up of a nitrogenous base, a phosphate group and a deoxyribose sugar. [1]
The function of DNA:
DNA is a molecule that carries genetic information in the form of genes, which is made up of a specific sequence of nucleotides that codes for the synthesis of specific polypeptides. [1]
State the significance of order of bases in a DNA molecule
Different order of bases result in different genes which codes for a different sequence of amino acids which codes for a particular polypeptide which determines a specific characteristic.
Compare and contrast between DNA and RNA. [4]
Similarities:
Made up of nucleotides as basic units [1]
Complementary base pairing rule [1]
Differences:
DNA is a double stranded molecule while RNA is a single stranded molecule. [11]
DNA contains thymine as a nitrogenous base while RNA contains uracil as a nitrogenous base instead of thymine.
DNA is a permanent molecule while RNA is a temporary molecule.
Describe and explain the impact of genetic mutation on the normal functioning of the organism. [4]
DNA mutation leads to change in mRNA sequence during transcription. [1]
Which will lead to different amino acid sequence being synthesised during translation. [1]
Different three-dimensional structure of protein formed. [1]
Loss of shape of active site and subsequent loss of function of protein. Enzyme is defective and cannot synthesise (melanin eg for albinism) [1]
Explain how you derived at the answers of composition of bases in DNA.
DNA is double stranded, thus the bases r paired following the complimentary base pair rule. Adenine pairs with thymine and guanine pairs with cytosine.
Define transcription and state the location in a mammalian cell where transcription occurs.
Transcription refers to the synthesis of messenger RNA from DNA template. It occurs in the nucleus.
Using a named example, describe how genetic engineering can be applied to allow organism to produce foreign proteins. [6]
Isolate gene of interest from cellular DNA and cut gene using restriction enzyme to produce two sticky ends. [1]
Cut a bacteria plasmid using the same restriction enzyme to produce two complementary sticky ends. [1]
Mix the gene of interest with the bacteria plasmid and anneal/ seal/ join them using DNA ligase, to form the recombinant plasmid. [1] Mix the recombinant plasmid and bacteria and apply temporary heat or electric shock to open up the pores on the cell membrane of the bacteria for the recombinant plasmid to enter the bacteria, forming the transgenic
bacteria. [1]
Mass produce the transgenic bacteria in large scale fermenters with optimum temperature, pH and nutrient conditions. [1]
Allow the bacteria to multiply and produce target proteins (transcription and translation of the gene of interest). Lyse the bacteria cell and extract and purify the target protein. [1]
OR
Isolate gene of interest from cellular DNA and cut gene using restriction enzyme to produce two sticky ends. [1]
Cut the viral DNA using the same restriction enzyme to produce two complementary sticky ends. [1]
Mix the gene of interest with the viral DNA and anneal/ seal/ join them using DNA ligase, to form the recombinant viral DNA. [1]
Mix the recombinant viral DNA and virus and apply temporary heat or electric shock to open up the pores on the cell membrane of the virus for the recombinant viral DNA to enter the virus, forming the transformed virus. [1] Mass produce the transformed virus in large scale fermenters with optimum temperature, pH and nutrient conditions. [1]
Inject the transformed virus into the target host (plant / fish / human). [1]
The virus will transfer the gene of interest into the genome of the host. [1]
The transformed host will express the gene of interest to produce the target protein via transcription and translation. [1]
State the advantages and disadvantages of genetic engineering. [4]
Genes from an organism can be inserted into non-related species or different species to express the desired trait. [1]
More efficient as transgenic organisms grow faster. [1]
Low cost mass production of medicines eg. Insulin mass production [1]
Development of food designed to meet specific nutritional goals. [1]
Production of crops that can adapt to grow in extreme conditions. [1]
Disadvantages:
Pests that feed on BT crops may adapt and develop resistance to the toxins in these crops, rendering this type of insecticides ineffective. [1]
Superweeds can be created when herbicide resistant plants cross-bred with wild weeds. Rapid growth and reproduction of these weeds can compete with the crops for space. [1]
The company that first engineered the GM seed can patent their GM food / gene therapy technology in obtaining economic monopoly to prevent others
from profiting. [1]
GE could introduce allergens in food. These cause a reaction from the immune system. [1]
The viral / bacterial vectors used during gene therapy may revert to virulent origin in causing diseases in host. [1]
Modifying a single gene in plants could result in the alteration of some metabolic processes within the plant. This could result in the formation of toxins not usually found in the plants. Consumption of these could pose
serious health problems. [1]
Gene inserted during gene therapy may cause DNA mutation in host, thus causing patient to develop cancer. [1] Genes that code for antibiotic resistance in the recombinant plasmid may
accidentally be transferred into pathogenic bacteria that cause disease to human, making antibiotics ineffective in treating these diseases. [1]
Lack of approval from certain religions regarding GE as it may not be appropriate to alter the natural genetic makeup of organisms. [1]
Define transgenic organism. [3]
A transgenic organism is an organism that has been genetically engineered [1] by insertion of a foreign gene [1] involving human intervention/ through artificial means. [1]
Compare the advantages of genetic engineering over selective breeding. [4]
Selective breeding vs Genetic engineering
SB: Organisms used must be closely related or of the same species
GE: Genes can be inserted into related or non-related species
SB: Defective genes may be
transmitted along with healthy genes to the offspring
or High possibility of producing genetically defective offspring
GE: Genes are carefully selected before being transferred
or Low possibility of genetic defects being passed down
SB: A slow process requiring breeding over several generations
GE: A rapid process involving reproducing individual cells
SB: Requires large spaces / amount of land
GE: Only requires a small area in a laboratory
SB: Less efficient process as organisms grow slowly or require more food
GE: More efficient as transgenic organisms grow faster and require less resources
Explain how a gene that controls production of human insulin can be inserted into bacterial DNA to produce human insulin.
- X(insulin) gene is isolated and cut using a restriction enzyme, producing 2 sticky ends.
- The same restriction enzyme is used to cut the bacterial plasmid, isolated from a bacterial cell, to produce 2 complementary sticky ends with complementary bases.
- The X(insulin) gene is mixed with the bacterial plasmid and annealed together by DNA ligase to form recombinant plasmid.
- Mix the recombinant vector with host cell/E.coli/bacteria
- Apply temporary heat or electric shock to open up the pores of the cell membrane of the bacteria to allow the recombinant plasmid to enter, forming transgenic bacteria.
Additional: (insulin)
Transgenic bacteria r cultured in large-scale fermenters w nutrient broth, optimum pH, optimum tempt and optimum conc of O2 to produce large amounts of insulin. The bacteria cells then burst(lyse) to release the insulin produced in the transgenic bacteria itself and insulin is extracted and purified.
Chromosome
A chromosome is a rod-shaped structure that is coiled and condensed. It is made up of a deoxyribonucleic acid (DNA) molecule wrapped around proteins (histones).
State advantage resulting from the use of genetically engineered bacteria in production process
High reproduction rate
Asexual reproduction -> reduces variation and results in purity of compound.
State an explain effect on ecosystem if genetically modified organisms r introduced into the wild
Loss of biodiversity
Other animals in food chain/web may lose food source or over populate due to loss of predator or disrupt the ecosystem
