Cells- WJEC AS Biology

Cell ultrastructure including organelles, prokarotic cells v eukaryotic cells

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  • Created by: ava.scott
  • Created on: 04-05-14 17:57

Nucleus

LARGE- usually takes up a lot of space in the cell.

Contains genetic material in the form of chromosones.

Double membrane (nuclear membrane), of which the seond is continuous with the endoplasmic reticulum. Also has pores for mRNA and other substances to move in and out.

Contains nucleolus which makes rRNA for ribosomes.

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Endoplasmic Reticulum

Rough

The Rough endoplasmic reticulum is coivered in ribosomes for protein synthesis.

It looks like flattened sacs surrounding cisternae.

It is continuous with the nuclear envelope.

It also transports coded polypeptides around the cell e.g. to the Golgi apparatus.

Smooth

No ribosomes

More tubular

Makes lipids

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The Golgi Apparatus

Also looks like flattened sacs surrounding cisternae, but smoother and more curved than the endoplasmic retiulum (ER.)

Vescicles pinched off from the ER fuse into the golgi body.

Here they are processed further (e.g. adding carbonhydrates to make glycoproteins), packaged and secreted in a vescicle for exocytosis.

They can also produce lysosomes, which carry digestive enzymes. They have to be completely undigestable. These enzymes are used to break down worn out organelles, or are secreted for digestive uses.

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Mitochondria

These are the site for aerobic respiration.

They are shaped like a jelly-bean. They have double membrane, and the internal membrane is folded into cristae, to increase surafe area. This surrounds a matrix, which contains substances for use in respiration.

The mitochondria also contain their own ribosomes and are responsible for their own protein synthesis.

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Cytoskeleton, Centrioles and Vacuoles

The Cytoskeleton is made of microfilaments and microtubules made from actin and tubulin.

It is responsible for organelle movement within the cell (e.g. chloroplasts moving to the most sunlight) and also whole cell movement.

Centrioles are small cylindrical structures that produce spindle fibres during cell division. They are absent in most plant cells.

Vacuoles are single membraned sacs of watery substances, that is used to store water and other substances, such as mineral ions.

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Chloroplasts

Chloroplasts also have a double membrane, but is not folded like mitochondrias.

The inner membrane surrounds a jelly-like space called the 'stroma'.

Chloroplast conatin thykaloids, which have very high surface area, and contain the chlorphyll pigment used in photosynthesis.

They also contain starch grains.

Also contains ribosomes for its own protein synthesis.

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Cell Walls

Cell walls give cells structure and let them become turgid. They are not found in animal cells.

Plants- The cell wall is made form cellulose, a polyshaccharide made from beta glucose.

Fungi- The cell wall is made from chitin, a mucosaccharide.

Prokaryote- The cell wall is made from murein.

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Prokaryote Cells (Bacteria)

Differences between Prokaryote and Eukaryote Cells:

  • Prokaryotes do not have any membrane bound organelles. Eukaryote do.
  • Prokaryotes don't have a nucleus containing DNA, instead they have circular/'chromosonal' DNA and plasmid DNA that floats freely in the cell.
  • Prokaryotes sometimes have a slime capsule that protects them from dehydration and phagocytes. This is neer present in eukaryotes.
  • Cell wall made from murein, rather than cellulose or chitin.
  • Prokayrote has smaller ribosomes.
  • Prokaryote sometimes have flagella to move them around.
  • The centrosome is the site for respiration, rather than mitochondria.
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Viruses

These have a protein capsid head surrounding a nucleic acid.

They are not techically alive, and only reproduce when in another cell, exploiting its protein synthesis mechanism.

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