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TOPIC 3 - Coggle Diagram
TOPIC 3
Cell Ultrastructure
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Nucleus: an enclosed envelope composed of two membranes perforated by pores. Contains chromosomes and a nucleolus.
rough endoplasmic reticulum (rER): A system of interconnected membrane bound flattened sacs. Ribosomes are attached to the outer surface.
cell surface membrane: phospholipid bilayer containing proteins and other molecules forming a partially permeable membrane
Smooth endoplasmic reticulum (sER): similar to rER but doesn't have any attached ribosomes. Smooth ER makes lipids and steroids.
Prokaryotic cell
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cell wall (made of murein): for shape, protection and transport
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flagellum: used for movement. hollow cylindrical thread-like structure, rotates
Golgi apparatus: stacks of flattened, membrane-bound sacs formed by fusion of vesicles from the ER. Modifies proteins and packages them in vesicles for transport.
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Lysosome: Spherical sacs containing digestive enzymes and bound by a single membrane. Involved in the breakdown of unwanted structures within the cell, and in destruction of whole cells when old cells are to be replaced or during development.
Centrioles: hollow cylinders made up of a ring of nine protein microtubules. They are involved in the formation of spindle fibres during nuclear division and in transport within the cell cytoplasm.
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Cell division
meiosis
Independent assortment allows genetic variation as homologous chromosomes pair up during meiosis I randomly meaning only one chromosome from each pair ends up in each gamete.
During the 1st meiotic division, the four chromatids come into close contact and break and rejoin at the chiasma. This exchanges DNA between non-sister chromatids.
mitosis
Prophase = the homologous chromosomes condemns and come together. The nuclear envelope breaks down and the spindle fibres form.
Metaphase = the chromatids line up along the cell’s equator and spindle fibres attach to each centromere.
Anaphase = the homologous pairs are separated and the spindle fibres shorten. At the end of anaphase the chromatids reach the poles and the spindle fibres break down.
Telophase = the nuclear envelope reframes and the chromosomes unravel so that the two steps of genetic information become enclosed in separate nuclei. Cytokinesis also occurs.
sexual reporduction
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The sperm is specialised as it has a flagellum to allow it to swim and the acrosome which is an adapted lysosome on the sperm’s head which contains hydrolytic enzymes to digest the follicle cells and the zone pellucid allowing the membranes to fuse. The egg is specialised as its has the jelly coat which hardens after one sperm has entered preventing polyspermy.
1) the has of the sperm contacts the jelly coat of the egg. This triggers the release of hydrolytic enzymes which dissolves the jelly coat and starts the acrosomal reaction.
2) Actin fibres begin to elongate and form the acrosomal process.
3)The acrosomal process elongated further and binds with the sperm binding receptors in the membrane. This binding causes the vitelline layer to begin to break down.
4) The membranes of the sperm and egg Fues. This causes the depolarisation of the membrane which turns off the sperm binding receptors. (preventing polyspermy)
5) The sperm nucleus enters the cell cytoplasm. The cortical reaction begins (the fusion of membranes causes cortical granules within the lysosome to fuse with egg’s plasm membrane and empty the chemical contents, causing the jelly coat to harden)
6) Conversion of the vitelline layer into fertilisation membrane (continuation of the cortical reaction). There is also an increase in cellular respiration and protein synthesis in the egg (egg activation)
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KEY TERMS
Chromatin: the combination of all the DNA and its associated proteins (histones) in the nucleus. It gets condensed into chromosomes during mitosis
Centromere: a region of DNA typically found near the middle of a chromosome where two identical sister chromatids come in contact. It is involved in cell division as the point of mitotic spindle
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Centrioles: organelles thats serve as the main microtubule organising centre of the animal cell as well as a regulator of the cell cycle progression
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root tip experiment
1) Cut 5mm of. Root tire from plant
2) Put the root tip in preheated acid
3) Add acetic orcein as a stain
4) Gently break open the root tip on a microscope slide and squash carefully
5) Look at the specimen under a microscope
stem cell therapy
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Differential gene expression: The expression (switching on/ transcription and translation) of different genes. Almost all of the cells in an organism are genetically identical but differential gene expression allows them to specialise
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embryonic stem cell
pluripotent stem cells: found after the first few divisions of the embryo (not including the placenta/ umbilical cord)
totipotent stem cells: found in the first couple of divisions of the embryo (including the placenta/ umbilical cord)
1) scientist propose that stems cells could be used to repair damaged tissue.
2) Regulatory bodies set up to investigate benefits and ethical issues surrounding stem cells.
3) Research proposals are investigated by HFEA to determine benefits vs ethical issues.
4) Licensed centres are set up to carry put stem cell research, carried out by trained staff and all work is regulated.
5) Guidelines and codes of practice are produced to ensure all scientists are working in a similar way.
6) Research is published and monitoring continues to make sure advances are publicised and guidelines are kept up to date.
7) Information and advice is given to the government to promote society’s understanding of what’s involved.
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genetics
polygenes
discontinuous variation
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eg Blood group, tongue rolling and gender
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continuous variation
Characteristics are controlled by genes at several differenet loci (polygenic) and can be on different chromosomes
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eg weight, height, hand span
dihybrid crosses
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A dihybrid cross involves drawing a punnet square to show the inheritance of the two genes from two parents
epigenetics
- literally means 'above genes'
- involves the modification to DNA or histones which cause genes to be activated or repressed
- DNA sequence is not changed but gene expression is
- Epigenetic control can be influenced by several factors including age and lifestyle
- It can cause cells to differentiate into different cells or result in diseases like cancer
Methylation of DNA
- Methyl group is added to DNA between C and G bases
- DNA can pack more tightly together. This causes proteins and enzymes needed for transcription to be able to bind
- The gene is not expressed
Acetylation of histones
- Acetyl groups can be added or removed from histones
- Adding acetyl groups makes DNA less condensed, exposing genes allowing them to be transcribed, because transcription factors and enzymes like RNA polymerase are able to bind more easily.
- Removing acetyl group make DNA more condensed, causing genes to be hidden and unable to be transcribed.
