Biology Topic 3 Summary

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  • Created by: paria
  • Created on: 02-06-13 16:11

Prokaryotic Cells

Prokaryotic cells do not have a nucleus or any other membrane-bound cell organelles. Examples are Bacteria and Cyanobacteria.

  • Infolding of cell surface membrane - photosynthetic membrane (site of respiration)
  • Plasmid - small circle DNA
  • Capsule - slimy layer on surface for protection and to prevent dehydration
  • Pili - thin, protein tubes allowing bacteria to adhere to surfaces
  • Flagellum - hollow cylindrical thread-like structure that helps move the cell
  • Cell Wall made of murein 
  • Their DNA is not associated with any proteins and lies free within the cytoplasm.
  • Ribosomes are present
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Eukaryotic Cells

Eukaryotic cells contain discrete membrane-bound organelles such as, nuclei, mitochondria and chloroplasts.

  • Nucleus - contains chromosomes and a nucleolus. The DNA in chromosomes contain genes that control the synthesis of proteins.
  • Rough Endoplasmic Reticulum - A system of interconnected membrane-bound flattened sacs. Ribosomes are attached to the outer surface, hence making it a rough ER. The ribomsomes are in control of synthesising protein.
  • Smooth Endoplasmic Reticulum - like rER, but doesn't have any attached ribosomes. SER is involved with making lipids & steroids. Found near the muscles and liver.
  • Ribosomes - made of RNA & protein. Found in the cytoplasm or attached to the endoplasmic reticulum.
  • Golgi Body - Stacks of parallel flattened-bound sacs formed by the fusion of vesicles coming from the rER. Modifies protein and packages them in vesicles for transport. 
  • Lysosome - spherical sacs containing digestive enzymes and bound by a single membrane. Involved in the breakdown of unwanted structures within cells and the descrution of old cells that are to be replaced.
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Eukaryotic Cells Continued

  • Cell surface membrane - phospholipid bilayer containing proteins and other molecules froming a partially permeable barrier
  • Mitochondria - Site of aerobic respiration (the production of A.T.P) Outer and inner membrane (double membrane). Containing their own genetic material. Inner membrane folds to form cristae, which is surrounded by a fluid matrix.
  • Chloroplast - found in plant cells only and are enclosed by a double membrane. Stroma contains a series of membrane-bound flattended sacs called thylakoid membranes. Contains starch grains (which act as a carbohydrate store), lipid stores and DNA, RNA and ribosomes - all involved in nucleic acid and protein synthesis. 
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Differences Between The Two

The Differences between Prokaryotic Cells and Eukaryotic Cells.

Prokaryotic cells are much smaller; their cell wall is made of murein whereas eukaryotic cells are made of cellulose (in plant cells only). Prokaryotic cells have no membrane-bound organelles, whereas eukaryotic cells do such as, choloroplasts (in plant cells only), nucleus, mitochondria, lysosomes and golgi body. Genetic material in prokaryotic cells is present, but in a single-circular DNA form, but no nucleus present, but in eukaroytic cells a nucleus enclosed by a double membrane is present with many linear DNA molecules forming chromosomes.

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Protein Transport In The Cell


  • Transcription of DNA to mRNA.
  • mRNA leaves the nucleus.


The golgi body appears as a stack of parallel flattened membrane pockets that are called cisternae, which are formed by vesicles coming from the rough endoplasmic reticulum and fuse into eachother. 

  • The ribosomes from the rER synthesise the protein
  • Once they are made they are sent up the lumen of the ER to be pinched off from its own membrane to form a vescile containing the protein.
  • This is then to fuse with other vesicles to form the flattened sacs of the golgi apparatus.
  • When the protein is secreted into the body it will undergo modification
  • Once modified it is ready to be enclosed to form a lysosome
  • The vesicle fuses with the cell surface membrane releasing the protein by the process of exocytosis
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Gametes are highly speciailiesd, with structures and functions that are different from other body cells.


  • large cell surface area (to increase the chance of fertilisation - a bigger target) that is in capable of independent movement
  • It is wafted along by ciliated cells lining the tubes and by muscular contractions of the tubes
  • The cytoplasm of the ovum contains proteins and lipid food reserves for a developing embryo
  • Surrounding the cell is a jelly-like coating called the zona pellucida
  • The presence of the zona pellucide is to prevent polyspermy
  • The presence of cortical granules is to produce the 'cortical reaction' is to also prevent polyspermy
  • The nucleus is a haploid to restore the diploid number of chromones 
  • Presence of nutrtients / food store / oill droplets - energy supplement / building blocks for growth
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  • Much smaller than an ovum and can move by itself
  • Tail to help move the sperm to targetted location - powered by energy released by the mitochondria
  • Membrane receptors to trigger acrosome reaction
  • Acrosomes contain hydrollytic enzymes (acrosin) to break down the follicle cells / zona pellucida
  • Nucleus - haploid to restore the diplod number of chromosomes after fertilisation
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When The Sperm Meets The Ovum

  • Sperm reaches the ovum
  • chemicals released from cells surrounding ovum trigggering the acrosome reaction
  • the acrosome swells fusing with sperm cell surface membrane
  • digestive enzymes in the acrosome are released
  • the enzymes digest through follicle cells and the zona pellucida
  • the sperm fuses with the ovum membrane
  • enzymes released from the lysosomes in the ovum (cortical reaction) thicken the jelly-like layer preventing polyspermy
  • The sperm nucleus enters the ovum 
  • nuclei of ovum and sperm fuse
  • meosis is completed
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The fusion of the sperm and the ovum membrane causes three important things to occur:

1. A temporary change in the electrical charge on the inside of the ovum membrane from negative to positive - neglecting any other sperm from entering.

2. The cortical reaction - where by cortical granules pass out of the ovum through the ovum membrane by exocytosis into the zona pellucida. This causes the zona to turn into a tough fertilisaion membrane

3. Completion of meiosis with meiosis II giving the female haploid nucleus and a second polar body.

1 and 2 prevent polyspermy: the result of multiple sets of chromosomes into the ovum.

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In progress


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