Organelles without membranes

What are ribosomes?
Spherical organelles that are 20nm in diameter and made of ribosomal RNA. They don't have a membrane.
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Where are ribosomes made?
In the nucleolus in two sub units that recombine in the cytoplasm.
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Where do you find ribosomes?
Some free in the cytoplasm and some attached to the RER.
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What function do the ribosomes on the exterior of the RER mainly serve?
Synthesising proteins for outside the cell.
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What function do the ribosomes in the cytoplasm mainly serve?
Assembling proteins inside for inside the cell.
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What are centrioles?
Two bundles of microtubules (which are tubulin protein subunits arranged in a cylinder) at right angles to eachother.
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What is the function of centrioles?
Before a cell divides, the centrioles form spindles from threads of tubulin and the chromosomes attach to these. Centrioles also form cilia by multiplying and lining up under the cell surface membrane and sprouting microtubules.
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From which type of cell are centrioles absent?
Higher plants although they may be present in some forms of green algae.
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What is the cellulose cell wall of plants made of?
Bundles of cellulose fibres.
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What does the cell wall do?
Provides strength and support to the cell but also the plant as a whole. It helps maintain the cells shape. It is also permeable to solutes and solvents.
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What are the cell walls of fungi made of?
chitin
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What is the cytoskelteon?
A network of protein structures in the cytoplasm consisting of microfilaments, microtubules and cytoskeletal motor proteins.
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Describe the microfilaments and what they do for the cell.
There are rod-like ones made of subunits of the protein actin and are 7nm in diameter. They provide strength to the cell and keep its shape stable. They allow it to move.
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Describe the microtubules and what they do for the cell.
They are straight, cylindrical, about 18-30nm diameter and made from subunits of the protein tubulin. They provide shape, support as well as a track for motor proteins (see next card) to walk on as well as cilia production, etc. as mentioned before.
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Describe motor proteins and what they do for the cell.
Myosins, kinesins and dyneins. They are molecular motors but also enzymes which have a site that binds to and allows hydrolysis of ATP for energy. They walk and drag organelles and other substances around the cell on the track formed by microtubules.
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Describe intermediate filaments and what they do for the cell.
They are made from a variety of proteins and are about 10nm in diameter. They anchor the nucleus but also extend between cells which allows cell to cell communication. They also help cells adhere to basement membranes, stabilising tissues.
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Other cards in this set

Card 2

Front

Where are ribosomes made?

Back

In the nucleolus in two sub units that recombine in the cytoplasm.

Card 3

Front

Where do you find ribosomes?

Back

Preview of the front of card 3

Card 4

Front

What function do the ribosomes on the exterior of the RER mainly serve?

Back

Preview of the front of card 4

Card 5

Front

What function do the ribosomes in the cytoplasm mainly serve?

Back

Preview of the front of card 5
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