Unit 4 Mixed Flashcards
What is the advantage of preventing self-pollination
Increases genetic variation and so increases the chances of survival of the species as it can adapt to a changing environment
Why is an even number of chromosomes needed to make a species fertile
Homologous pairs and bivalents can form during prophase 1 of meiosis and so gametes can be produced
Intron
Non coding region of DNA
is spliced out and not translated
Exon
Coding regions which are translated for a polypeptide
What are the potential problems of using a virus in gene therapy
Can cause an immune response
May not reach the target cell
May become pathogenic
May affect other genes - oncogenes
What are the disadvantages of using a molecular patch to treat DMD
• it is not permanent and so repeated treatments are needed
• the change is not present after cell replication and so is not passed onto next generation
Ethical issues of germ line therapy
• unknown long term effects
• possible activation of oncogenes
• the modified genes are passed onto the next generation and so will effect later generations
Antigen
Innates an immune response and the production of antibodies
What is an antigen-antibody complex
When a specific antibody is bound to an antigen
How can the sperm enter the secondary oocyte
Acrosome reaction
The acrosome releases hydrolytic enzymes such as proteases which hydrolyse the corona radiata and zona pellucide
How is polyspermy prevented
Cortical reaction
The cortical granules rupture and the zona pellucida thickens and hardens to form the fertilisation membrane
Continuous variation
Polygenic
Imtermediates
Discontinuous variation
Monogenic
Distinct groups
How does natural selection work
• variation is caused due to mutations
• some mutations will confer a selective advantage
• individuals with selective advantage is more likely to survive and reproduce and pass on advantageous alleles to offspring
• this is repeated over several generations and the allele frequency of the advantageous allele will increase
Sympatric speciation
Non-geographical barriers
Allopatric speciation
Geographical barriers
How do isolation barriers work
• prevent the gene flow
• genetic differences will accumulate and so they can no longer produce fertile offspring
Umbilical artery
Carries blood away from foetus
Contains carbon dioxide, urea
Umbilical vein
Carries blood to the foetus
Contains oxygen, nutrients and antibodies
Ethics of prenatal diagnosis
• more selective abortions
• moral status of the foetus
• may cause harm to foetus
• may give a false negative
Conditions required for germination and why
• water - cause cotyledons to swell and to dissolve substances to act as a fluid medium for enzymes
• oxygen - for aerobic respiration to produce ATP for metabolism
• suitable temperature- to increase rate of diffusion and to increase enzyme activity
Germination of non-endospermic seeds
• endosperm has been absorbed into cotyledons
• amylase digest starch in the cotyledons to maltose
• proteins and fats are also broken down into amino acids, fatty acids and glycerol
• these move into the plumule and radicle and are used for cell division for growth
Germination of endospermic seed
• starch, proteins and fats are in the endosperm
• the embryo produces gibberellin which moves into the aleurone layer
• the GA causes enzymes to break down proteins into amino acids which are used to synthesise other proteins such as amylase which breaks down starch in the endosperm into maltose
What is gene therapy
The treatment of genetic disease by replacing defective alleles in a patient with copies of a new DNA sequence
Somatic cell therapy
• therapeutic genes are transferred into somatic cells
• the modification and effects are restricted to the individual only and cannot be passed on through gametes
• DNA is introduced into the target cells by a vector such as plasmid or virus
Germ line therapy
• sperm or egg is modified
• allows therapy to be heritable
• rare due to ethical and technical reasons
Gene therapy to treat Duchenne muscular dystrphy
Use of the drug disapersen
Exon skipping - a molecular patch is introduced over the exon with the mutation which makes the gene readable again
• a shorter form of dystrophin is produced but it is more functiona
What is tissue engineering
The study of growth of new connecting tissues or organs from cells and a collagenous scaffold to produce a fully functional organ for implantation back into the donor host
Scaffolds used in tissue engineering
• artificial structures that support 3D tissues
• allow cells to attach and move
• deliver and retain cells and biological molecules
• are porous to allow diffusion of nutrients and waste
• biodegradable and can be adsorbed by the surrounding tissues
What is a stem cell
An undifferentiated cell capable of dividing to give rise to daughter cells which can develop into different types of specialised cell or remain as undifferentiated stem cells
Sources of stem cells
Embryos and bone marrow
Embryonic stem cells
Totipotent so can differentiate into all types of cells
Adult stem cells
Pluripotent so cannot differentiate into all types of cells
What is recombinant DNA
DNA produced by combining DNA from 2 different species
What are restriction enzymes
Bacterial enzymes that cut up any foreign DNA that enters a cell
Cut is staggered with short, single-stranded fragments called sticky ends at either ends
How to a gene inserted into a plasmid using restriction enzymes
- Bacterial plasmid contains 2 marker genes (one for ampicillin resistance and the other that is rendered non-functional if DNA is successfully inserted into it)
- Plasmid is cut open using a restriction enzyme
- Foreign DNA is cut with the same restriction enzyme to ensure complementary sticky ends
- DNA is inserted using DNA ligase which joins the sugar backbone of the 2 sections of the DNA together
- Ensure bacteria have a plasmid with a donor gene
Preparing a fragment of DNA containing a human gene using reverse transcriptase
- Reverse transcriptase produces a complimentary or cDNA from a mENA template
- A human regulator sequence which controls gene expression is replaced by a bacterial regulator and so the cDNA is inserted
- Once expressed in bacterial cells the insulin can be purified for use
What problems does producing cDNA overcome
• locating the gene
• restriction enzymes cutting the gene into non-functional fragments
• the presence of introns as prokaryotes dont have introns
• the need for post-transcriptional processing to produce functional mRNA
Advantages of genetically engineered bacteria
• allows for the production of complex proteins or peptides which cant be made by other methods
• can be used to produce medicinal products such as insulin
Disadvantages of genetically engineered crops
• is complicated and expensive
• can be hard to indentify genes in a genome
• the synthesis of a required protein may involve many genes each coding for a polypeptide
• using restriction enzymes produces millions of non-useful fragments
• not all eukaryotic genes will express themselves in a prokaryotic cell
Hazards of genetically engineered bacteria
• bacteria can readily exchange DNA and so antibiotic resistance could be transferred to pathogens
• the possible transfer of oncogenes
Advantages of GM crops
• better keeping qualities
• higher yield due to the increased growth rates, improved nutritional value, ease of management, tolerance of unfavourable conditions
• less pesticide use due to resistance of pathogens and insects
Disadvantages of GM crops
• genetic contamination - herbicide resistance could spread to wild relatives and form superweeds
• misuse of pesticides
• corporations controlling agriculture
Hazards of GM crops
• reduces biodiversity by changing natural gene pools
• there are unknown effects of eating new protein
Advantages of stem cells
• can be produced quickly and on a large scale
• produces genetically identical cells for transplant which reduces the risk of rejection
Disadvantages of stem cells
• expensive and unreliable
• unknown long term effects
• inadvertent selection of disadvantageous alleles
Ethics of stem cells
• an embryo mist be destroyed to obtain the cells
• may be used for non-medical purposes
State the function of the tapetum
Provides nutrients for the developing pollen
Provides a waterproof outer coat for the pollen grains
Function of tube nucleus in growth of pollen tube
Controls the pollen tube
Controls the synthesis of hydrolytic enzymes
Role of mitosis and meiosis in the formation of the female gamete
• megaspore mother cell undergoes meiosis
• forms four haploid cells
• one of these cells undergoes three mitotic divisions
• one of the these cells become the oosphere, 2 fuse and produce a diploid polar nucleus, 3 form antipodals and 2 form synergids
Why is fertilisation in plants referred to as double fertilisation
• one male gamete fuses with the oosphere to produce a diploid zygote
• the other male gamete fuses with the diploid polar nucleus to produce a triploid endosperm nucleus
What information has been obtained from the Anopheles and Plasmodium Genome Projects
• the DNA sequence code
• the location of genes on chromosomes
• the complete DNA sequence
Uses of the information obtained from the genome projects of Anopheles and Plasmodium l
• make plasmodium susceptible to insecticides
• make mosquitoes less fertile
• prevent transmission
• modification of Plasmodium to reduce pathogenticity
• development of more effective drugs or vaccines
Proto-oncogene
Genes which can mutate to oncogenes which cause cancer
What is epigenetics
The control of gene expression
What is a stem cell
An undifferentiated cell that has the ability to become specialised cells
How does DNA methylation result in tumour growth
mRNA from regulator not produced so regulator protein not produced
The suppressor gene is not expressed so there is uncontrolled cell division
How do cancer cells switch the suppressor genes off
Remove acetyl groups from histones so the DNA becomes tightly coiled and so RNA polymerase can’t access the gene and so cannot be transcribed
What is the consequence of tumor suppressor genes becoming permanently switched off in all cells in the body
Increases the risk of cancer which can be passed onto the next generations
FSH
Follicle development
LH
Causes ovulation
Role of prolactin in women
Stimulates cells in mammary glands to secrete milk into ducts
Why is oxytocin production during birth is an example of positive feedback
• stimulates contraction of myometrium which stimulates the release of more oxytocin which increases the contractions
How a cDNA fragment containing a human gene can be prepared
• extract mRNA from the bacterium
• use reverse transcriptase to synthesise a single strand of cDNA using the mRNA as a template
• use DNA polymerase to produce double stranded DNA
• add sticky ends to ends of each DNA strand of the DNA
• copy the DNA many times using PCR
How does genetically engineered plasmids be produced
• plasmids from a bacteria are isolated
• restriction enzyme such as restriction endonuclease is used to open the plasmid at a specific point which produces sticky ends which are complementary to the DNA
• DNA ligase is used to bind the DNA into the plasmid
• antibiotic resistance marker genes are used to select bacteria containing the recombinant plasmids
Natural barriers to infection in the body
• ciliated mucous membranes
• skin microflora
• lysozyme in tears, saliva and mucus
• low stomach pH
• skin connective tissue
• inflammation- blood clotting, phagocytes
Why is the body sometimes described as a host to other living organisms
Many organisms live in or on the human body
How do phagocytes and T lymphocytes bring about the cell-mediated response against a virus
• macrophages engulf the virus infected cell by phagocytosis and present the antigen on their surface
• colonal expansion of T cells causes their proliferation into T helper, T killer and T memory
• T killer cause cell lysis
• cytokines stimulate phagocytosis
Why can antibiotics be used to treat bacterial infections and not viral infections
• antibiotics act on cell walls of bacteria
• antibiotics affect the metabolism carried out by bacteria
• viruses do not have cell walls or a metabolism and so are not affected by antibiotics
Why is it unlikely that a vaccine for the common cold will ever be developed
• high mutation rate and so there are many strains and antigenic types
• vaccines need to contain antigens from all strains to provide complete immunity
• each antigen must produce a strong immune response
Why is it unethical to make the flu vaccine compulsory for all
• religious objections
• fears of safety and side effects
• individual rights
• some may be too ill for vaccination due to HIV or chemotherapy
Where does spermatogenesis occur
Seminiferous tubules
Process of spermatogenesis
Germinal epithelium cells (2n) divide by mitosis to form spermatogonia (2n) which divide by mitosis to form primary spermatocytes (2n) these undergo meiosis I to form secondary spermatocytes (n) which undergo meiosis II to form spermatids (n) which mature into spermatozoa (n)
Function of interstitial cells
Secrete testosterone which stimulates the process of spermatogenesis
Function of steroli cells
Provide nourishment and protection to cells during spermatogenesis
Head of a sperm
About 5um
• haploid nucleus
• acrosome
Midpiece of sperm
Contains lots of mitochondria to provide ATP for movement
Tail of sperm
50 um
• moves in a circular motion to propel
Where does oogenesis occur
• in the ovary up until the secondary oocyte
Process of oogenesis
Before birth
• germinal epithelium cells (2n) undergo mitosis to form oogonium (2n) which undergo mitosis to form Primary oocyte (2n) which undergoes meiosis I up until prophase I
After puberty
• meiosis I is complete and a secondary oocyte (n) and a first polar body is produced (n). The secondary oocyte undergoes meiosis II up until metaphase II
After fertilisation
• meiosis II completes and an ovum (n) and a second polar body (n) is produced
What surrounds primary oocytes
Germinal epithelium cells which form the primary follice
What surrounds the secondary oocyte
The primary follicle develops into a secondary follicle which matures to a Graafian follicle which migrates to the surface and bursts which releases the secondary oocyte
What happens to Graafian follice when it is an ovum
Becomes the corpus luteum
Process of fertilisation
- Spermatozoa move into the Fallopian tubes
- Capacitation - cholesterol and glycoproteins are removed from the cell membrane over the acrosome which increases the permeability of the membrane
- Acrosome reaction - protease is released and digests the corona radiata. Once the sperm head is in contact with the zona pellucida the acrosome ruptures and releases acrosin which hydrolyses the zona pellucida
- Sperm head entry - cell membrane of the sperm and oocyte fuse and the male nucleus starts to enter the oocytes cytoplasm
- Cortical reactions - cortical granule membrane fuse with oocyte cell membrane and the membrane expands and hardens to form the fertilisation membrane which prevents polyspermy
- 2nd meiotic division completes and the ovum is formed
- Mitosis occurs as material is combined to make diploid cells of the embryo called a zygote
What is implantation
Sinking of the blastocyst into the endothelium
Process from fertilisation to implantation
• cleavage - the zygote undergoes repeated mitotic division to form a ball of 16 cells called a morulla by day 3
• by day 7 a blastocyst forms and has an outer layer of cells called a trophoblast which develops trophoblastic villi which penetrate the endometrium and increases the surface area for absorption of nutrients from the endometrium
Implantation window
The endometrium is receptive to accept implantation of the blastocyst as the endometrium is thick
About 8-10 days post ovulation
Process of double fertilisation
• a compatible pollen grain lands on the stigma and germinates in the sucrose solution secreted by stigma and a pollen tube is produced
• the pollen tube grows out of the pollen grain through a pit, down the style and up a gradient of chemoattractants.
• the pollen tube nucleus codes for the production of hydrolases (cellulases and proteases) and digests its way through the tissues of the style and the products of digestion is used by the growing pollen tube
• the pollen tube grows through the micropyle and passes into the embryo sac
• the pollen tube nucleus then disintegrates and the tip of the tube opens to release the 2 male gametes into the embryo sac
• first male gamete enters the embryo sac and fuses with the oocyte to form a diploid zygote
• second male gamete fuses with the diploid polar nucleus and forms a triploid primary endosperm nucleus
Dicotyledons
Eg broad beans
• non-endospermic seeds as the endosperm is absorbed into the cotyledons
Monocotyledons
Eg maize
Endospermic seed
Endosperm is the food source
Plumule
Developing shoot
Radicle developing root
Why must seedlings be moved away from the parent plant
Seedling would be outcompeted by more successful parents which can obtain water and minerals from soil and cast a shade over the seedling
Non-endospermic germination
• water is embibed through the micropyle which causes the cotyledons to swell so the testa splits so more oxygen can diffuse in for respiration
• starch and proteins in the cotyledons are mobilised through hydrolysis into maltose and amino acids
• these products provide energy for the plumule and radicle for growth
Endospermic germination
• water absorbed through micropyle
• gibberellin in the cotyledon are released by the embryo and diffuse into the aleurone layer
• GA induces the transcription of DNA and the mRNA is translated into hydrolytic enzymes
• proteases hydrolyse proteins into amino acids which are used to form amylase and maltase
• amylase diffuses out of the aleurone layer and hydrolyses starch in the endosperm into maltose then glucose
• these diffuse to embryo where radicle and plumule use glucose for aerobic respiration
Pollen grain development
Diploid mother cell undergoes meiosis to form a tetrad of 4 haploid pollen cells
Each of these undergo mitosis to form a generative nucleus and a tube nucleus
The generative nucleus undergoes mitosis to form 2 male nuclei
Function of tapetum
A specialised layer of nutritive cells which provides nutrition to developing pollen grains
What is dehiscence
The opening of the anther which releases the pollen grains
Process of dehisence
Anther outer layers mature and dry out so outer walls curl away which exposes the pollen grains
The lateral grooves open up and form a gap called the stomeum
The pollen sacs are opened
Where is ovule produced
Ovary
Another word for ovule
Megaspore
Where are female gametes formed
Within embryo sac within nucellus
Process of ovule development
• megaspore mother cell (2n) undergoes meiosis to produce 4 haploid cells
• 3 degenerate
• 1 of the haploid cells undergo 3 mitotic divisions to form 8 haploid cells
• 2 combine to form a diploid polar nucleus, 3 form antipodals, 2 syngerids and 1 forms the oosphere
What is pollination
The transfer of pollen grains from the anther to the mature stigma of a plant from the same species
What is self-pollintation
When a pollen is transferred to the stigma of the same plant
What is cross-pollination
When pollen from one plant is transferred to the stigma of a different plant
How is cross-pollination promoted
• chemical self-incompatibility
• dichogamy
Dichogamy
Stamen and stigma ripen at different times
Protandry
Stamen ripens first
Protogyny
Stigma ripens first
Follicle stimulating hormone
• stimulates maturation of follicle
• stimulates oestrogen production
• is secreted by anterior pituitary gland
Luteinising hormone
Initiates ovulation
Stimulates the formation of the corpus luteum
Inhibits oestrogen
Secreted by anterior pituitary gland
Oestrogen
• stimulates secretion of LH
• stimulates the uterus to produce a new endometrium
• inhibits FSH
• secreted by the ovary
Progesterone
• maintains the endometrium
• stimulates oestrogen secretion
• inhibits FSH and LH
• secreted by the corpus luteum
Amnion
A membrane which is derived from the inner cell mass of the blastocyst
The foetus is enclosed within the amnion
Around week 4-5, the amniotic fluid is produced bu the mother
About 4 months - foetus contributes urine to it
Function of amniotic fluid
• shock absorber - protection
• maintains the foetus’ temperature
• provides lubrication
• allows movement so muscles and bones function before birth
Hormones during pregnancy
• Human chorionic gonadotropin is secreted by the embryo maintains the corpus luteum for the first 16 weeks and so endometrium is maintained
• placenta secretes high levels of oestrogen and progesterone and so FSH and LH are inhibited
• progesterone inhibits oxytocin
• oestrogen stimulates growth of uterus to accommodate growing foetus and stimulates the growth and development of mammary glands during pregnancy
Hormones during birth
• oestrogen increases
• progesterone decreases - myometrium can now contract as oxytocin is released by the posterior pituitary gland and works by positive feedback
• prolactin is secreted by the anterior lobe of the pituitary gland during and after birth to stimulate the production of milk by mammary glands
Aneuploidy
Loss or gain of single chromosome
Polyploidy
Changes in number of whole sets of chromosomes
What is the function of hCG in pregnancy
Maintain the corpus luteum
How did the results of the human genome project made the use of gene editing possible
• identification of the position of all genes
• base sequence of normal genes found
Double fertilisation in plants
• first male gamete fuses with female gamete to produce a zygote
• second male gamete fuses with the polar nucleus to form the triploid endosperm nucleus
