SNAB: Topic 3

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  • Created by: Joe
  • Created on: 25-01-12 15:37


Golgi Apparatus

Golgi apparatus is found in eukaryote cells of both animals and plants.

Stacks of flattened, membrane bound sacs formed by fusion of vesicles from the endoplasmic reticulum.

Job: modfies proteins and other molecules and then packages them into transport vesicles.


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They are found in eukaryote cells in animal cells.

Lysosomes are spherical sacs which contain digestive enzymes, they are separated from the rest of the cell by a plasma membrane so that the digestive enzymes will not digest the proteins and lipids within the cell.

Job: Their job is to help in the breakdown of undesiriable structures found in the cell, and are also used in the destruction of whole cells when old cells are to be replaced during developement e.g. bone cells.

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Smooth Endoplasmic Reticulum

Smooth ER is found in eukaryote cells in both plants and animals.

A system of interconnected membrane-bound flattened sacs.

Job: Involved in the synthesis of lipids and steriods.

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Rough Endoplasmic Reticulum

Rough ER is found in eukaryote cells in both plants and animals.

A system of interconnected membrane-bound, flattened sacs. Ribosomes are attached to the outer surface. proteins made by these ribosomes are transported thorugh the rough ER to other parts of the cell.

Job: Involve in protein synthesis (translation).

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Nucleolus are found in eukaryote cells in both plants and animals.

A dense body within the nuclues; where ribosomes are made.

Job: Synthesises ribosomes


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Ribosomes are found in prokayrotes and eukaryotes in animal, plant and bacteria. However in bacteria the ribosomes are not the same as plant and animal ribosomes and are known as 70S ribosomes in bacteria.

Made of RNA and protein, they are found free in the cytoplasm, or are attached to rough endoplasmic reticulum; they are the site where protein synthesis occurs.

Job: To join amino acids to together (synthesize proteins). 

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Cell Surface Membrane (plasma Membrane)

Found in eukaryote cells in both plants and animals.

Made up of a phospholipid bilayer containing proteins and other molecules forming a partially permeable barrier.

Job: Regulates what enters and exits the cell and ensure that desired/ neccessary substances are kept within the cell.

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Found in eukaryote cells in both plants and animals.

Enclosed by an envelope composed of two membranes perforated by pores ( Nuclear pores). Contains chromosomes and a nucleolus. The DNA in chromosomes contains genes that control the sunthesis of proteins.

Job: Regulates all the processes that happen in the cell.

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Found in eukaryote cells, however only in animal cells.

Every animal cell has one pair of centrioles, which are hollow cylinders made up of a ring of nine protein microtubules (Arranged in a helix formation to form a hollow tube).

Job: Involved in the formation of the spindle during nuclear divsion and in transport within the cell cytoplasm.

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This is found in eukaryote cells in both animals and  plants.

Mitochondria are surrounded by an outer and innner membrane; they also contain their own genetic code, so that when a cell divides the mitochondria also replicate themselves under control of the nucleus. The inner of its two membranes is folded to form finger-like projections called cristae.

Job: To convert glucose into energy through cellular respiration (aerobic respiration) using water and oxygen. The cell can then use the energy created or the mitochondira can then store the energy in the bonda of a chemical called adenosine triphosphate (ATP) that the mitochondria has created.

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Mitosis : Prophase

1) Chromosones condense and become visible

2) Each chromosone is made up of two chromatids

3)Centrioles move and spindle starts to form

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Mitosis : Metaphase

4) Nuclear envelope disappears

5) Centrioles reach the two poles and spindle is completed

6) Chromosones are fully condensed

7) Microtubules move centromeres to equator

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Mitosis : Anaphase

8) Centromeres split

9) Microtubules pull chromatids apart

10) Chromatids of each chromosone pulled to opposite poles

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Mitosis : Telophase

11) Chromatids are now called chromosones

12) Chromosones reach poles

13) Nuclear envelope forms around both new groups of chromosones

14) chromosones decondense (No longer visible by microscope)


15) Cytoplasm divides into two

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Plant Tissues

Schlerenchyma Fibres: Long, thin plant cells which are tapered at both ends. Sclerenchyma fibres help to provide plants with support. They have cell walls which are thickened with lignin. They do not have living contents.

Collenchyma tissue: A type of supporting tissue found in plants. Collenchyma cells are slightly elongated and have their cell walls strengthened with extra cellulose at the corners.

Parenchyma: Relatively unspecialised tissue found in plants. Parenchyma cells have thin cellulose cell walls and living contents. These cells are very important in providing support in young stems

Stomata (Stoma): A pore, found in the leaf and stem epidermis that is used for gas exchangee. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the opening.

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Plant Tissues

Xylem: Carry water and inorganic ions up through the stem. The walls of xylem vessels contain lignin which provides them with extra strength.

Pholem: Transports sugars made photosynthesis by the leaves and transports them up and down the cell. Phloem provides a mass flow system for transport of the products of photosynthesis.

Vascular Bundle: In the stems and leaves of young plants, particularly those which are not woody, the vascular tissue is found in bundles. These vascular bundles contain xylem vessels, which transport water and mineral ions up the stem to the leaves and phloem tubes.

Ground Tissue: Contains cells specialised for photosynthesis, storage and support.

Epidermis: The epidermis is a single layer of cells surrounding the other tissues in the roots, stems and leaves.

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How Xylem Vessels Are Made

The plant produces a polumer called lignin. The lignin then impregnates the cellulose cell wall and the cell then slowly becomes lignified, during this process the entry of water and solutes is restriced into them.

Near the same time the tonoplast breaks down and there is autolysis of the cell's contents. The cell organelles, cytoplasm and cell surface membrane are broken down by the action of the enzymes and are lost; the cell dies.


The end walls bewteen cells of the column are lost or become highly perforated.

Long tubes are formed and form continuos pathways from the roots to the leaves.

The cellulose microfibrils and the lignin in the cell walls of the xylem vessels gives the tubes great strength.

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Stem Cells

Pluripotent:  Pluripotent cells are able to give rise to many types of specialised cell. The cells that make up the inner mass of a blastocyst are known as pluripotent embryonic stem cells.

Totipotency: Totipotent cells can give rise to any type of specialised cell. We all started life as a single cell or zygote. This zygote divides by mitosis. After it has undergone three mitotic divisions there will be eight cells present. Each of these totipotent embryonic stem cells can give rise to any of the specialised cells which make up the adult human body.
The meaning of totipotent is easy to remember. Totipotent cells have the potential to give rise to a total individual.

 Multipotent:  We all started life as a multipotent single cell or zygote. As we grew and developed into adults, our cells became specialised for different purposes. The process by which cells become specialised is called differentiation. In adults, some cells still have the ability to differentiate and give rise to a variety of cell types. These cells are called multipotent stem cells. Multipotent stem cells in bone marrow develop into different sorts of blood cell.





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Fertilisation Process

1) The sperm reaches the ovum

2) Chemicals released from the cells surrounding the ovum, triggering the acrosome reaction

3) The acrosome swells, fusing with the sperm cell surface membrane

4) Digestive enzymes in the acrosome are released

5)The enzymes digest through the follicle cells

6) And the jelly like layer surrounding the ovum

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Fertilisation Process Continued

7) The sperm fuses with the ovum membrane

8) The sperm nucleus enters the ovum

9)Enzymes released from lysosomes in the ovum thicken the jelly like layer     preventing entry of other sperm

10) Nuclei of the sperm and ovum fuse forming a zygote

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Prokayote Cells

The prokayote kingdom consists of bacteria and cyanobacteria.

  • Cells do not have nuclei or other membrane bound organelles
  • Does not have a true nucleus
  • Diameters between 0.5 and 5 (x10^-6) m

Parts of a prokayote

  • Ribosomes                                  Cell Wall
  • Circular DNA                                Infolding of cell surface membrane
  • Small loop of DNA (Plasmid)       
  • Capsule
  • Flagellum
  • Pili
  • Cytoplasm
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Eukaryotes have a diameter of 20(x10^-6)m and up

Found within eukaryotes:

  • Cytoplasm
  • Rough ER
  • Smooth ER
  • Nucleolus
  • Nucleus
  • Mitochondria
  • Centrioles
  • Lysosomes
  • Golgi apparatus
  • Cell Membrane
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Production of Proteins

1) Transcription of DNA to mRNA

2) mRNA leaves the nuclues. (Through the nuclear envelope)

3) mRNA attaches to ribosomes where a polypeptide chain is formed

4) Protein synthesised on ribosomes enters rough ER

5) Protein moves through the rough ER and assumes its 3d shape en-route

6) Vesicles pinched off the rough ER contian protein and fuse to form the flattened sacks of the golgi apparatus

7)Proteins are modified within the golgi apparatus

8)Vesicles pinched from the golgi contain the modified protein and then fuse with the cell membrane  secreting the protein, e.g. extra cellular enzymes

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Human Fertilisation

1) Sperm reaches the ovum

2) Chemicals released from the surrounding cells trigger the acrosome reaction

3) The acrosome swells fusing with the sperms cell membrane

4) Digestive enzymes in the acrosome are released

5) The enzymes digest throught the follicle cells and then the zona pellucida

6) The sperm fuses with the ovum membrane

7) The sperm nucleus enters the ovum

8) Enzymes released from the ovum cause the zona pellucida to thicken

9) Nuclei of the sperm and ovum fuse forming a diploid nuceus (2N)

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Plant Reproduction

1) Fertilisation takes place in the ovary sac found in the ovule

2) The pollen grain germinates on the style and a pollen tube grows down through the style to the ovaries

3) The generative nucleus divides to form two haploid gamete nuclei which move down the pollen tube

4) The tube grows through a microscopic pore into the embryo sack, the two male gamete's enter the nuclei

5) One of the male gametes fuses with the egg's nuclei and fuses to for a diploid nucleus (Zygote (2N)), and the second fuses with the two polar nuclei found within the embryo sac forming a triploid nucleus (3N)

The triploid nucles becomes the food storage (Endosperm) and the zygote an embryo.

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Organisation of DNA into Chromosones

1) DNA (Double helix)

2) DNA winds around a protein

3) DNA and protein coil to form a chromatin fibre

4) Chromatin fibres attaches to scaffolding protein forming loops

5) Folding of the protein scaffolding produces the condensed structure seen during nuclear divison

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Switching Genes On

1) RNA polymerase binds to a section of the DNA adjacent to the gene to be transcribed. (This section is known as the promoter region)

2) Only when RNA polymerase has attached to the DNA will transcription proceed

3) The genes remained switched off until the enzyme attaches to the promoter region successfully.

Note: The attachment of a regulator protein is usually also required to start the transcription process.

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Protein Recognition

1) Cells have specific recognition proteins which allow them to recognise other cells which are the same and stick to them. These are known as adhesion molecules.

2) A small part of each recognition protein is embedded within the cell surface membrane, a larger part extends from the membrane

3) This exposed section binds to complementary proteins on the adjacent cell

If cells from different tissues are separated and then mixed together they will reform into tissues as the recognition proteins bind.

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Switching Genes Off

Transcription of a gene can be prevented by a protein repressor molecule, by attaching to the promoter region of the DNA.

In addition protein repressor molecules can attach to the regulator proteins themselves preventing them from attaching.

Both methods cause genes to not be transcribed.

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