Topic 3 - Voice of the Genome Flashcards
Smooth ER
Membranes that form flattened sacs. Similar to rough ER but without the ribosomes. Used for synthesis and processing of lipids
Rough ER
A system of membranes enclosing a fluid filled space. Folds and processes proteins that have been made at the ribosomes
Lysosome
Membrane-bound organelle that contains digestive enzymes. Used to break down worn out components of the cell
Mitochondrion
Double-membrane bound organelles found in eukaryotic cells. Contain enzymes needed for respiration and is where ATP is produced
- inner membrane folded into finger-like projections called cristae
- contains 70S ribosomes
Golgi apparatus
Fluid filled flattened sacs. It processes and packages new lipids and proteins into vesicles for transport. Makes lysosomes.
Nucleus
A double-membraned organelle that contains the genetic material of a cell in the form of chromatin
- chromatin is made of protein and DNA
- the pores in the nuclear envelope allow substances to move between the nucleus and the cytoplasm
Centriole
Hollow cylinders containing a ring of microtubules. Organises microtubules to form spindle fibres, which help with the separation of chromosomes during cell division
Mitosis
the process by which a cell divides to produce two genetically identical daughter cells
Asexual reproduction
the production of genetically identical offspring from a single parent or organism
Sexual reproduction
the production of offspring that are genetically different from the parent organism or organisms by the fusing of two gametes
Meiosis
a type of cell division that only occurs in gametes, and results in the formation of four genetically unique haploid daughter cells, each with half the number of chromosomes as the diploid parent cells
Histones
positively charged proteins involved in the coiling of DNA to form dense chromosomes in cell division
Nucleosomes
dense clusters of DNA wound around histones
Karyotype
a way of displaying an image of the chromosomes of a cell to show the pairs of autosomes and sex chromosomes
Cell cycle
a regulated process of three stages (interphase, mitosis and cytokinesis) in which cells divide into two genetically identical daughter cells
Interphase
the period between active cell divisions when cells increase their size and mass, replicate their DNA and carry out normal metabolic activities
G1 - growth and protein synthesis
S - DNA replication
G2 - further growth and protein synthesis
Cytokinesis
the final stage of the cell cycle before the cell enters interphase again - division of the cytoplasm at the end of mitosis to form two independent, genetically identical cells
Chromatid
one strand of the replicated chromosome pair that is joined to the other chromatid at the centromere
Prophase
the first stage of active cell division where the chromosomes are visible and coiled up and consist of two daughter chromatids joined by the centromere; the nucleolus breaks down
Metaphase
the second stage of active cell division where chromosomes line up at the equator and spindle fibres attach to centromeres
Anaphase
the third stage of active cell division where the centromeres split so chromatids become new chromosomes; they are moved to the opposite poles of the cell, centromere first, by contractions of the microtubules of the spindle
Telophase
the fourth stage of active cell division where a nuclear membrane forms around the two sets of chromosomes, the chromosomes unravel and the spindle breaks down
Centromere
the region where a pair of chromatids are joined and which attaches to a single strand of the spindle structure at metaphase
Metaphase plate (equator)
the region in the middle of the cell along which the chromosomes line up
Clones
genetically identical individuals resulting from asexual reproduction in a single parent
Mitotic index
the ratio between the number of cells in a tissue sample that are in mitosis and the total number of cells in the sample
Nucleolus
the region of the nucleus where ribosomal RNA (rRNA) is assembled into ribosomes
Ribosomes
small organelles that are either free in the cytoplasm or attached to the rER (only in eukaryotic cells)
the site of protein synthesis and made of protein and rRNA
Organelles in the ultrastructure of eukaryotic cells
- nucleus
- nucleolus
- ribosomes
- rough and smooth endoplasmic reticulum
- mitochondria
- centrioles
- lysosomes
- Golgi apparatus
Organelles in the ultrastructure of prokaryotic cells
- cell wall
- capsule
- plasmid
- flagellum
- pili
- ribosomes
- mesosomes
- circular DNA
Prokaryotic cell wall
The cell’s rigid outer covering made of peptidoglycan. Provides the cell with strength and support.
Prokaryotic slime capsule
a thick polysaccharide layer used for protection against dessication (drying out) and phagocytosis
Prokaryotic plasmid
small, circular rings of double-stranded DNA
Prokaryotic flagellum
a tail-like structure which rotates to move the cell
Prokaryotic pili
thread-like structures on the surface of some bacteria that enable attachment to other cells or surfaces, allowing exchange of plasmids
Prokaryotic mesosomes
Inward folds in the membrane of bacteria which are used for respiration
Prokaryotic circular DNA
a type of synthetic DNA that forms a closed loop structure, with no free ends
Egg cell adaptations
- zona pellucida forms an impenetrable barrier after fertilisation to prevent other sperm nuclei entering the egg cell
- cytoplasm contains protein and lipid food reserves for the developing embryo
- follicle cells nourish the ovum and help it interact with its environment
Sperm cell adaptations
- acrosome contains enzymes to digest through the zona pellucida and cell membrane of an egg cell
- flagellum enables sperm to swim to the egg
Acrosome reaction
The process by which the sperm binds to the zona pellucida and releases digestive enzymes contained in the acrosome to penetrate through it
Cortical reaction
The process by which cortical vesicles located just beneath the plasma membrane release cortical granules into the space between the membrane and the zona pellucida, hardening it and preventing polyspermy
Steps in fertilisation
- sperm meets zona pellucida and acrosome reaction occurs
- sperm head fuses with cell membrane of egg, allowing the sperm nucleus to enter the egg cell
- cortical reaction occurs
- nuclei fuse and full set of chromosomes is restored
Locus
the position of a gene on a chromosome
Linkage
When genes are close together on the same chromosome, they are linked. They are not independent of each other and are often inherited together as independent assortment does not separate them.
Sex linkage
the inheritance of traits determined by genes located on the sex chromosomes
- most sex linked traits are located on the X chromosomes with there being no equivalent locus on
the Y chromosome - therefore, inheritance of genes depends on the sex of the individual
Chromatin
DNA in its decondensed form that forms chromosomes
Crossing-over
The process by which non-sister chromatids on lined up homologous pairs intersect and exchange sections of genetic material, resulting in new combinations of alleles. The point where they intersect is called the chiasma.
Independent assortment
the process by which homologous pairs of chromosomes line up at the equator randomly, leading to many different combinations
Mitosis steps
Prophase - chromosomes become visible and the membrane of the nucleus breaks down. The nucleolus disappears, the spindle forms, and centrioles move to either end of the cell
Metaphase - chromosomes, each consisting of two sister chromatids, line up at the equator. They attach to spindle fibres, which are attached to centrioles
Anaphase - spindle fibres contract, pulling the chromatids apart
Telophase - chromosomes decondense and become invisible; membrane of nucleus and nucleolus reform
Stem cells
unspecialised cells with the potential to develop into different cell types in the body
Pluripotent
stem cells that can differentiate into any cell type, excluding the placenta and embryo
Totipotent
stem cells that can differentiate into any cell type including the placenta and embryo
Use of embryonic stem cells
- when embryo consists of 8 identical cells, it is totipotent
- when embryo becomes blastocyst, the 50 cells in the blastocyst are pluripotent
- huge potential as they can differentiate into almost any cell type
- embryos used for research are often the waste (fertilised) embryos from IVF treatment
- embryos have potential to develop into human beings (ethical objection)
Use of adult stem cells
- only able to produce limited cell types (e.g. bone marrow, brain)
- less controversial and donor can give consent
- chance of rejection if acceptor is not similar to donor in terms of blood type and body antigens
Use of stem cells in medicine
- ethically questionable as it leads to a viable embryo being destroyed
- official regulatory authorities help make decisions by comparing the benefits and ethical issues of stem cell research
Jobs of regulatory authorities
- Reviewing proposals for scientific research that uses stem cells
- Licensing and monitoring of stem cell research centres
- Providing guidelines and codes of practice
- Monitoring developments in scientific research
- Providing info to professionals
DNA methylation
- enzyme adds methyl group onto a cytosine in the promoter region
- this prevents transcription as RNA polymerase cannot attach to the promoter region
Transcription factors
Regulator proteins that, when present, will bind to the promoter region of a gene
When attached, they either allow or prevent RNA polymerase from attaching to form mRNA (activator/repressor)
Histone modification
- DNA helices wind around histones to form chromatin
- when tightly wound, transcription is prevented
- addition of acetyl group or methyl group to a histone opens up the chromatin to allow transcription
Lac operon model
No lactose present
- repressor protein attaches to promoter region
- gene coding for β-galactosidase is switched off
- RNA polymerase cannot attach
- no transcription/mRNA
- no β-galactosidase produced
Lactose present
- lactose attaches to repressor protein so promoter region is not blocked
- gene coding for β-galactosidase is switched on
- RNA polymerase attaches
- transcription/mRNA
- β-galactosidase produced
Cell specialisation through differential gene expression
- under right conditions some genes are activated and others inactivated
- mRNA is only transcribed from active genes
- mRNA translated into proteins
- proteins modify the cell
- changes to cell by proteins cause the cell to become specialised
Genotype
The genetic makeup of an organism
Phenotype
observable characteristics of an organism which are the result of the genotype as well as environmental factors
Polygenic inheritance
The inheritance of multiple different alleles at multiple loci that control a single phenotype
Continuous variation
traits that show a range of phenotypes without distinct categories, typically influenced by multiple genes (polygenic inheritance) and environmental factors
Discontinuous variation
traits that have distinct, separate categories with no intermediates, usually controlled by a single gene (monogenic inheritance) and are not significantly affected by the environment
Cell theory (Schleiden and Schwann)
- all living organisms are made up of one or more cells
- cells are the basic functional unit in living organisms
- new cells are produced from pre-existing cells
Transmission EM features
- electrons pass through the specimen
- electrons picked up by electromagnetic lens
- higher magnification and resolution possible
- 2D image
- cross-section of specimen used so organelles and their internal structures are visible
- require dead specimens
Scanning EM features
- electrons pass across the specimen
- electrons picked up by electromagnetic lens
- lower magnification and resolution
- 3D image
- image of whole specimen or thick sections of specimens can be viewed
- require dead specimens
Crossing over (detail)
- homologous chromosomes pair up to become bivalents (connected homologous chromosomes)
- non-sister chromatids cross over at the chiasma and get entangled
- entanglement places stress on DNA molecule, resulting in a section breaking off and joining another chromosome
- this creates new allele combinations of chromosomes
Independent assortment (detail)
- homologous chromosome pairs are arranged randomly at the equator
- orientation of homologous pair is independent of arrangement of other pairs
- chromosomes are pulled apart to the poles
- allele combination of each daughter cell depends on alignment of homologous chromosomes
- this creates different allele combinations
Operon
A cluster of genes under the control of a promoter
Protein trafficking steps
- amino acids made into protein on the ribosomes
- newly made protein stored and folded in rER cavity
- protein being packaged at the ends of rER. Membrane closes forming a vesicle
- Vesicles pinch off the rER and transport protein towards Golgi
- Protein is modified at Golgi
Epigenetics
heritable changes in DNA/gene function without changes to the base sequence of DNA
Benefits to stem cell therapy
- can treat a wide range of diseases/conditions
- organs call be developed, which reduces need for organ donors
- adult stem cells are already widely used in a range of treatments
Risks to stem cell therapy
- stem cells cured in lab could become infected and transmitted to a patient
- low number of stem cell donors
- use of embryonic stem cells destroys embryos
- should the embryo be treated as a person or a commodity? who owns them? etc.
