TOPIC 2: CELLS, VIRUSES AND REPRODUCTION Flashcards
The Cell Theory
- All living things are made up of cells
- cells are the basic subunits of life
- All cells are formed from pre-existing cells
Tissue
A group of similar cells that perform the same function.
Organ
A group of tissues that carry out a specific function
Organ System
A group of organs that collectively perform a function
Eukaryotic cell
A cell with a nucleus and membrane-bound organelles
Prokaryotic cell
A cell that does not have a nucleus or membrane-bound organelles.
What organelles are found in eukaryotic cells
- Nucleus
- Rough Endoplasmic Reticulum
- Smooth endoplamic Reticulum
- 80 s ribosomes
- Mitochondria
- Golgi Apparatus
- Centrioles
- Lysosomes
What organelles are found in bacteria
- Cell wall
- Slime capsule
- Plasmid
- Flagellum
- Pili
- Ribosomes
- Mesosomes
Nucleus
Surrounded by a double membrane (the envelope) The nucleus also contains chromosomes, and a nucleolus, which is the site of ribosome production.
Rough Endoplasmic Reticulum
A series of flattened sacs enclosed by a membrane with ribosomes on the surface. The RER folds and processes proteins made on the ribosomes.
Smooth Endoplasmic Reticulum
A system of membrane-bound sacs. The SER produces and processes lipids
Golgi Apparatus
A series of fluid-filled, flattened and curved sacs with vesicles surrounding the edges. The Golgi apparatus processes and packages proteins and lipids. It also produces lysosomes.
Mitochondria
oval shaped, double membrane (the envelope) and is the site for aerobic respiration. The inner membrane is folded to form projections called cristae, with matrix on the inside containing the enzymes needed for cellular respiration.Prpduces ATP
Centrioles
Hollow cylinders containing a ring of microtubules arranged at right angles to each other. Centrioles are involved in cell division.
Ribosomes
Composed of two sub-units. Large sub-unit and Small sub-unit. The site of protein synthesis where long chains of amino acids are put together.
Lysosomes
vesicles, containing hydrolytic enzymes, bound by a single membrane.
Cell Wall
The cell’s rigid outer layer provides the cell with strength and support and maintains shape.IN plants the cell wall is made up of cellulose whereas in prokaryotes the cell wall is made up of peptidogylycan
Plasmid
circular piece of DNA.
Flagellum
a tail-like structure which rotates to move the cell.
Pili
hair-like structures which attach to other bacterial cells.
Mesosomes
infoldings of the inner membrane of bacteria which contain enzymes required for respiration.
Gram positive Bacteria
Gram Positive bacteria have a cell wall made up of a thick layer of peptidoglycan which retains crystal-violet stain.
Gram negative Bacteria
Gram Negative bacteria have a thin layer of peptidoglycan with an outer lipopolysaccharide membrane. The outer membrane of Gram negative bacteria is impermeable to antibiotics such as penicillin. It also does not retain crystal-violet stain.
Advantages of electron microscopes
Can magnify and resolve better
Disadvantages of electron microscopes:
- You have to put the sample in a vacuum, so you can’t magnify living things.
- Very expensive and not portable.
Light microscopes
Beam of light through the thin specimen objective lens and eyepiece lens magnify it.
Differences and similarities between transmission electron microscope and Electron Microscope
Beam of electrons through the object. TEM produces a 2D image whereas an Electron microscope produces a 3D image. You have to use a very thin specimen for a TEM. Ultrastructure structures only visible through a TEM. Electron microscopes show more however due to their shorter wavelength giving them a higher resolution. You have to stain samples for both types of microscope.
Stains for Light Microscope
methylene blue, iodine solution, orcein stain You stain to improve contrast so you can see cell structures one from another.
Describe the ethical implications of using untested drugs on people
- Side effects
- Difficult to obtain informed consent
- Deciding who gets the drug can be difficult people may feel disadvantaged or angry if they are not selected
Magnification
The extent to which an object has been enlarged by a microscope
Resolution
The ability to distinguish between points that are very close together
State the principles of the cell theory
- All living things are made of cells
- Cells are the basic subunits of life.
- All cells are formed from pre-existing cells
chloroplast
Site of photosynthesis and uses energy from the sunlight to form Glucose.
cell membrane
phospholipid bilayer that controls what goes in and out of the cell.
Vacuole
membrane enclosed sac that maintains cell structure
Differences between Light microscopes and Electron Microscopes
- Light microscopes are beams of light,lower magnification and resolution, can view living organisms, cheap.
- Electron microscopes are beams of electrons, Higher magnification and resolution, cant view living organisms, expensive
Describe the Lytic Viral cycle
- Virus attaches to the host cell and injects it nucleic acid into the cell.
- The host DNA is inactivated and the phage DNA takes over the hosts biochemistry.
- Viral DNA is replicated and new viral components are synthesised.
- Viral components assemble and host cell lyses.
What is Viral Latency
A period of time when a virus is part of the reproducing host cell, but does not affect it adversely.
Explain how antivirals work on viruses.
Antivirals inhibit viral replication in the host, they cannot affect viruses themselves as they are not living
Explain the most effective methods used in viral disease control.
- Rapid identification of disease
- Treating in isolation
- Preventing transmission between organisms eg. Washing hands
- Wearing protective clothing
- Identifying contacts
- Sterlizing and disposing of equipment after contact
State the name of the 3 stages of the cell cycle.
interphase, mitosis and cytokinesis.
State what happens in the three stages of interphase in the cell cycle.
- G1 - cytoplasm increases in volume by producing new proteins and cell organelles. Some genes are switched on. Pre-mRNA is formed and edited into mature mRNA.
- S phase - semi-conservative replication of DNA. Chromosomes become chromatids joined at the centromere. New histones are synthesised.
- G2 - DNA is checked for errors and corrected if possible. If corrected the cell further synthesises proteins and cell organelles. If not then the cell is paused in the G2 phase and will not move onto mitosis.1
Describe what happens in each of the stages of mitosis.
- Prophase: Sister chromatids condense, nuclear membrane breaks down, spindle fibres form
- Metaphase: Spindle fibres attach to the centromere and pull chromatids to the equator of the cell.
- Anaphase - Spindle fibres contract, the centromere splits, sister chromatids are separated and chromosomes pulled to opposite poles of the cell
- Telophase: Spindle fibres break down, nuclear membrane reforms around two sets of chromosomes, chromosomes decondense.
State what happens during cytokinesis.mitosis
Contractile fibres tighten around the centre of the cell, the cytoplasm splits in two producing two genetically identical diploid daughter cells
Describe what happens in each of the stages of meiosis.
- Prophase 1 - Sister chromatids condense, homologous pairs line up forming bivalents, crossing over occurs at the chiasma
- Metaphase 1 - Nuclear membrane breaks down, spindle fibres form, spindle fibres pull bivalents to the equator.
- Anaphase 1 - Spindle fibres contract, bivalents are separated and one pairs of chromatids are pulled to opposite poles.
- Telophase 1 - Nuclear membrane reform, spindle fibres break down, chromosomes decondense
- Prophase 2 - Sister chromatids condense and centrioles duplicate.
- Metaphase 2 - Nuclear membrane breaks down, spindle fibres form, spindle fibres pull sister chromatids to the equator of the cell.
- Anaphase 2 - Spindle fibres contract, centromere splits separating sister chromatids, chromosomes are pulled to opposite poles
- Telophase 2 - Chromosomes decondense, nuclear membrane re-forms, spindle fibres break down and cytokinesis occurs
Explain how meiosis leads to variation.
- Independent/random assortment - bivalents line up at the equator completely at random
- Crossing over - sections of DNA are exchanged at the chiasmata between non-sister chromatids within a homologous pair
Using a named example, explain how genetic mutations occur as a result of translocation.
Translocation occurs when sections of DNA from one homologous pair breaks off and reattaches to a different homologous pair
E.g. translocation between chromosome 8 and 14 results in Burkitt’s Lymphoma (cancer of white blood cells)
Using a named example, explain how non-disjunction can lead to polysomy and monosomy.
- When homologous pairs fail to separate in meiosis non-disjunction occurs.
- Polysomy is when the zygote contains more copies of a chromosome. E.g. Down’s Syndrome where there are 3 of the 21st chromosome
- Monosomy is when the zygote contains only one copy of a chromosome. E.g. Turner’s Syndrome where there is 1 X chromosome
Describe the stages of human fertilisation from contact of the sperm cell in the vagina
- When the sperm makes its way up the oviduct and uterus capacitation occurs changing the surface of the head of the sperm removing the glycoprotein.
- This triggers the acrosome to swell and fuse with the cell surface membrane of the sperm releasing its hydrolytic enzymes (acrosome reaction)
- Enzymes digest the zona pellucida layer so the sperm can reach the secondary oocyte.
- The cell membrane of the secondary oocyte and sperm fuse.
- Cortical granules are released from the secondary oocyte by exocytosis which causes the zona pellucida to harden (this prevents polyspermy)
- The nucleus of the secondary oocyte is stimulated to complete meiosis 2.
- The two haploid nuclei fuse forming a diploid zygote.
Explain how female gametes are produced in plants
- Diploid megaspore mother cell divides by meiosis to form 4 haploid megaspores
- Three of the haploid megaspores disentegrate
- The nucleus of one megaspore divides by mitosis 3 times to form the immature embryo sac.
- The cytoplasm of the immature embryo sac divides to form the mature embryo sac containing 3 antipodal cells, two polar nuclei, two synergid cells and the haploid female gamete.
Explain how male gametes are produced in plants
- Diploid microspore mother cell divides once by meiosis to form 4 haploid microspores
- Each microspore divides once by mitosis to form the pollen grain containing 1 haploid tube nucleus and 1 haploid generative nucleus (this is now a pollen grain)
Describe how double fertilisation occurs in plants.
- Pollen grain land on the stigma, it absorbs water, swells and splits open.
- The tube nucleus leads the formation of the pollen tube through the style
- The generative nucleus follows the tube nucleus, divides by mitosis forming 2 haploid male gametes
- When the pollen tube teaches the ovule, it breaks into the embryo sac and the tube nucleus disintegrates
- Double fertilisation occurs - 1 male gamete fuses with the two polar nuclei to form a triploid primary endosperm nucleus
- 1 male gamete fuses with the female gamete to form the diploid zygote. The other nuclei disentegrate
What is the difference between Gram positive and Gram negative Bacteria
- Gram positive bacteria - Thick peptidoglycan cell wall which retains crystal-violet stain.
- Gram negative bacteria - Thin peptidoglycan cell wall and outer lipopolysaccharide layer which does not retaincrystal-violet stain
Explain the significance of meiosis in living organisms
- Source of genetic variation because it involves independent assortment and crossing over
- Crossing over-Enables contribution of alleles from two individuals
- Independent assortment -produces new combinations of alleles.
4 .Genetic variation allows organisms to adapt to environmental change
What does endemic mean?
idea that species is found only in one specific area
Describe the process of crossing over that occurs during meiosis.
- Homologous chromosomes line up
- chiasmata form
- alleles/genetic information exchanged between chromatids
Advantages of Mitosis
can produce large numbers of offspring and does not need another organism to reproduce rapidly
Explain the term recessive allele
- Both alleles have to be present in order for the recessive phenotype to be expressed.
- Alleles are different forms of a gene with the same locus
Compare Oogenesis and spermatogenesis
- Oogonia are formed in embryo long before birth whereas spermatogonia are formed from the time of puberty throughout adult life.
- Each month from puberty to menopause each Oogonium forms one secondary oocyte- the others degenerate whereas in spermatogenesis four sperm are formed from each spermatogonium and millions of sperm are formed daily.
- Meiosis 2 reaches prophase and then stops unless fertilisation occurs whereas in spermatogenesis meiosis 1 and 2 are completed during sperm production.
- The graafian follicle releases a secondary oocycte into the oviduct at ovulation whereas in spermatogeneis millions of sperm are released from by the body by ejaculation.
- Oogenesis produces non-motile gametes whereas in spermatogenesis motile gametes are produced
What is the tonoplast
- Found in Plant cells
- The tonoplast is the membrane that surrounds the central vacuole of the plant.
- The tonoplast keeps the vacuole acidic this is important as it allows the vacuoles enzymes to break down food matter
- The tonoplast also actively pumps pottasium in and out of the vacuole
What do all Viruses have?
- A core of nucleic acid
2. A protein coat called a capsid
What is the nature of the nucleic acid in lambda bacteriophage and how does it copy its nucleic acid
Nucleic acid: Double stranded DNA
Copying of Nucleic acid:
Double-stranded DNA transcribed to mRNA
What is the nature of the nucleic acid in the Tobacco mosaic virus and how does it copy its nucleic acid
Nucleic acid: Single stranded RNA
Copying of Nucleic acid:
RNA copied directly to form mRNA
What is the nature of the nucleic acid of the Ebola Virus and how does it copy its nucleic acid
Nucleic acid: Single-stranded RNA
Copying of Nucleic acid: RNA copied directly to form mRNA
What is the nature of the nucleic acid of the Human immunodeficiency virus and how does it copy its nucleic acid
Nucleic acid: Single-stranded RNA
Copying of Nucleic acid: RNA reverse transcribed into double-stranded DNA, which is incorporated into the host cell’s DNA and later transcribed to form mRNA
What are the three types of viruses
- DNA viruses: Lambda bacteriophage
- RNA Viruses: Ebola and TMV
- Retroviruses: HIV these have a protein capsid and a lipid envelope
Describe the cycle of replication of the retrovirus HIV
- HIV has glycoproteins that attach onto the T-helper cell and binds to the cd4 receptors on the surface.
- HIV virus envelope fuses with cell surface membrane of T-helper cell
- Reverse transcriptase catalyses the reverse transcription of HIV RNA forming viral DNA from RNA template
- HIV DNA is integrated into T-cell DNA using the enzyme Integrase
- Protease splices HIV proteins and is combined with HIV RNA to make new viruses
