Cell structure and Division

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Cell-surface (plasma membrane)

Description:

Found in the surface if animal cells and just inside the cell wall of other cells. Mainly made up of lipids and protein.

Function:

Regulates the movement of substances into and out of the cell.

Has receptor molecules, to allow it to respond to chemicals like hormones.

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Nucleus

Description:

Surrounded by nucelear envelope (double membrane) containing many pores.

Contains chromosomes and nucleolus. (makes ribosomes)

Function:

Controls the cell's activites.

Instructions to make proteins.

Pores allow substances to move between nucleus and cytoplasm

(http://media.buzzle.com/media/images-en/gallery/botany/plants/600-cell-nucleus-diagram.jpg)

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Mitochondrian

Description:

Double membrane, inner one folded to form cristae

Inside is the matrix which contanis enzymes for respiration.

Function:

Site of aerobic respiration, where ATP is produced.

Very active and require a lot of energy.

(http://3.bp.blogspot.com/-LDSudNidWH4/UQAoVjnpRII/AAAAAAAACaY/CgMREGZYrhM/s1600/Mitochondria_detailed.gif)

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Chloroplast

Description:

Found in plant and algal cells

Surrounded by a double membrane

Function:

Site of photosynthesis

Absorb sunlight

(http://www.sciencekids.co.nz/images/pictures/plants/chloroplastdiagram.jpg)

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Golgi Vesicle

Description:

A small fluid-filled sac in the cytoplasm, surrounded by a mebrance and produced by golgi apparatus.

Function:

Stores lipids and proteins made by the Golgi apparatus 

Transports them out of the cell via cell surface membrane

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Golgi Apparatus

Description:

A group of fluid-filled, membrane bound flattened sacs.

Vesicles seen at the edges

Function:

Processes and packages new lipids and proteins

Makes lysosomes

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Lysosome

Description:

Round organelle surrounded by a membrane with no cler internal structure

Type of golgi vesicle

Function:

Contains digestive enzymes: lysozymes used to digest invading cells or brek down worn out components.

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Ribosome

Description:

Small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum.

Made up of proteins and RNA

Function:

Site where proteins are made

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Rough Endoplasmic Reticulum (RER)

Description:

A system of membranes enclosing a fluid-filled space

Surface covered with ribosomes.

Function:

Folds and processes proteins that have been made at the ribosomes.

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Smooth Endoplasmic Reticulum (SER)

Description:

Similar to RER but has no ribosomes

Function:

Transports, sythesisesand processes lipids.

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Cell Wall

Description:

A rigid structure that surrounds cells in plants, algae and fungi.

Plants: Mainly made of cellulose

Fungi: Mainly made of chitin

Function:

Supports cell and prevents them from changing shape.

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Cell Vacuole

Description:

Membrane-bound organelle found in cytoplams of plant cells.

Contains cell sap

Surrounded membrane: tonoplast.

Function:

Helps to maintain pressure inside the cell and keep cell rigid.

Stops plants from wilting.

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Prokaryotic cells

Flagellum: Long hair-like structure that rotates to make the prokaryotic cell move.

DNA floats free in the cytoplasm, its circular DNA is presented as one long coiled up strand.

Plasmids: Small loops of DNA that aren't part of the min circular DNA molecule. Contain genes for things like antibiotic resistance, and can be passes between prokaryotes.

Capsule: Pretects bacteria from attack by cells of the immune system.

Cell wall: Supports the cell and prevents it from changing shape. Made of murein.

No membrane-bound organelles.

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Binary Fission

The cell replicates its genetic mterial before physically splitting into two daughter cells.

1. Circular DNA and plasmids replicte.

    Main DNA loop is only replicated once, but plasmids can be replicated loads of times.

2. Cell gets bigger and DNA loops move to opposite poles.

3. The cytoplasm divides.

4. The cytoplasm divides and two daughter cells are produced.

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Virus replication

Viruses use their attachment proteins to bind to complementary receptor proteins on the surface of host cells.

Different viruses have different attachment proteins and therefore require different receptor proteins on host cells. Some viruses only infect on type of cell.

Viruses don't undergo cell division, they inject their DNA or RNA into the host cell. Then it uses its machinery to replicate viral particles.

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Optical microscope and Electron microscope

Optical microscope

  • Use light to form an image
  • Have a maximum resolution of about 0.2 micrometres
  • Can't use to view organelles smaller them 0.2 micrometres
  • Maximum magnification is about x1500

Electron microscope

  • Use electrons to form an image
  • They have a higher resolution than optical microscopes so give more detaild image
  • Maximum magnification is about x1,500 500
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Transmission electron microscopes (TEM)

  • Use electromagnets to focus a beam of electrons, which is then transmitted through the specimen.
  • Denser parts of the specimen absorb more electrons, which makes them look darker.
  • High resolution so you can see the internal structure of organelles
  • Only used on thin specimen
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Scanning electron microscopes (SEM)

  • SEMs scan a beam of electron across the specimen. This knocks off electron from the specimen, which are gathered in a cathode ray tube to form an image.
  • 3D images
  • Can be used on thick specimens
  • Lower resolution images than TEM.
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Homogenisation

Breaks up the plasma membrane and releases organelles into solution.

Solution must be:

Ice cold: reduce enzyme activity that breaks down organelles

Isotonic: Same concentration of chemicals as the cells being broken down to prevent damage to the organelles through osmosis

Buffer solution: Maintain pH

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Filtration

Filtered through a gauze to separate any large cell debris or tissue debris, like connective tissue from the organelles.

Organelles are much smaller than debris so they pass through the gauze.

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Ultracentrifugation

To separate a particular organelle from others.

1. Cell fragments poured into a centrifuge and spun at low speed.

  • Heaviest organelles (nuclei) go to bottom and form a pellet
  • The rest of the organelles stay suspended in the fluid above the sediment (Supernatant)

2. Supernatant is drained off, poured into another tube and spun at a higher speed. 

  • Next heaviest is mitochondria, which forms a pellet

3. Process is repeated at a higher speed until all are separated out

Nucleus>Mitochondria>Lysosomes>ER>Ribosomes

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Mitosis

  • Parent cell divides to produce two genetically identical daughter cells
  • Needed for growth of multicellular organisms and for repairing damaged tissues.

Interphase: period of cell growth and DNA replication

G1:cell grows and new organelles and proteins are made.

S: Synthesis, cell replicates its DNA ready to divide by mitosis.

G2: Cell keeps growing and proteins needed for cell division are made.

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Interphase

  • The cell carries out normal functions, but also prepares to divide.
  • The cell's DNA is unravelled and replicated, to double its genetic content.
  • Organelles are also replicated so it has spare ones, and its ATP content is increased
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Prophase

  • Chromosomes condense, getting shorter and fatter
  • Spindles form
  • Nuclear envelope breaks down
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Metaphase

  • Chromosomes line up on the equator 
  • Become attached to the spindle by their centromere
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Anaphase

  • The centromeres divide, separating each pair of sister chromatids.
  • Spindles contract, pulling chromatids to opposite poles of the spindle
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Telophase

  • Chromatids reach opposite ends of poles on the spindle.
  • Uncoil and become thin again (called chromosomes again)
  • A nuclear envelope forms around each group of chromosomes
  • Now 2 nuclei
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Cytokineses

  • Cytoplasm divides
  • Two new daughter cells that are genetically identical to original cell and each other
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Uncontrolled Cell Division

  • Cancer is caused by uncontrolled cell division:
  • If there is a mutation in a gene that controls cell division, the cells can grow out of control.
  • Cells keep on divinding to make more cells, which form a tumour.
  • Cancer is a tumour that invades surrounding tissues.

Cell cycle targets for cancer treatments:

G1: Chemotherapy prevent the synthesis of enzymes needed for DNA replication, if not produced, the cell is unable to enter the S phase, disrupting the cycle and forcing the cell to kill itself.

S phase: Radidation and some drugs damage DNA. At points in the cell cycle the DNA in the cell is checked for damage. If damage is detected the cell will kill itself.

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Comments

LisaCCapon

Found this really useful :) thank you

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