OCR Biology Unit 1 Notes-Cells, Exchange & Transport

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Cytoskeleton-network of protein fibres within cells that provide an internal framework and give mechanical strength, shape, structure and stability to the cells. Some of the fibres are called actin filaments, found in muscle cells which are able to move against each other. These cause the movement in some white blood cells. Other fibres are known as microtubules, which are cylinders about 25nm in diameter, made of tubulin. They can be used to waft a liquid past a cell or move a cell through a liquid. Other proteins present on microtubules move organelles and other cell contents along the fibres (which is how chromosomes are moved during mitosis, and how vesicles move from the ER to the golgi apparatus.) Think of these proteins as microtubule motors, which use ATP.

Undulipodia (in eukaryotes), flagella (in prokaryotes) and cilia with reference to microtubules: each one made from 9 microtubules arranged in a cylinder. They can move because they use energy from ATP. Flagella are made of a spiral of protein (called flagellin) which is attached by a hook to a protein disc at the base. Using energy from ATP, the disc rotates, spinning the flagellum.

Division of labour: some cells produce hormones, which are chemical messengers which help coordinate the activities of the whole organism. The instructions to make the hormone are in the DNA in the nucleus. The specific instruction is the gene, which is found on a chromosome. The nucleus copies the DNA instructions into a molecule called mRNA, which leaves through a nuclear pore and attaches to a ribosome. The ribosome reads these instructions and uses the code to assemble the hormone. The assembled protein is then pinched off into a vesicle and transported to the golgi, where it is then modified and packaged and moved to the cell surface membrane, where it is secreted outside.

1. Copy of mRNA instructions made in the nucleus.
2. mRNA leaves through nuclear pores.
3. mRNA attaches to ribosome, which then reads the instructions to assemble the protein.
4. The vesicles are pinched off and transferred to the golgi.
5. Vesicles fuse with the golgi.
6. The golgi modifies and packages the protein.
7. The vesicles is pinched off and move towards the cell surface membrane.
8. The vesicle fuses with the cell surface membrane.
9. The cell surface membrane opens to release the molecules contained in the vesicle.

Eukaryotic cells-have a nucleus, can contain two membranes, have membrane bound organelles, large ribosomes, linear chromosomes (separate strands) of DNA, DNA surrounded by a membrane, ATP production takes place in the mitochondria, larger, cell wall made of cellulose.

Prokaryotic cells-no nucleus, one membrane, no membrane bound organelles, small ribosomes, DNA in single loop free in liquid, ATP in infolded regions, smaller, murein cell wall.

Some prokaryotes help: e.g. bacteria like yoghurt and cheese, help with vitamin K production in animal intestines, skin covered in bacteria (prevents harmful organisms from getting in.)

5 roles of membranes: separate cell contents from cytoplasm, separate cell contents

Comments

Beth

Really helpful - Thanks!

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