Microtubule
Diameter-25nm
Made of -A tube of tubulin protein subunits
Function- form spindle fibres which cause the movement of chromosomes during cell division
-form tracks for the movement of vesicles
-form Eukaryotic cilla and flagella
Microfilament
Diameter-7nm
Made of -Helical strands of actin subunits
Function- - causes cell movement + changes in cell shape
- involved in cytokinesis
- length + shorten’breading’
Intermediate filament
Diameter -8-10nm
Made of - Many different types of protein (eg keratin) in a:
variety of deformable filaments
Function-form part of the scaffolding inside the cell providing mechanical strength
Roles of the cytoskeleton
1) The microtubules and microfilaments support the cell’s organelles, keeping them in position.
2)
3)
They also help to strengthen the cell and maintain its shape.
As well as this, they’re responsible for the movement of materia within the cell. For example, the movement of chromosomes when they separate during cell division depends on contraction of microtubules in the spindle (see pages 60-62 for more on cell division).
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The proteins of the cytoskeleton can also cause the cell to more.
For example, the movement of cilia and flagella is caused by the cytoskeletal protein filaments that run through them. So in the case of single cells that have a flagellum (e.g. sperm cells, the cytoskeleton propels the whole cell.
The cytoskeleton is dynamic (constantly changing), which
Centrioles
• Present in animal cells but not plant cells
-A pair of short hollow cylinders at right angles to each other
• Made of microtubules - same arrangement as basal body of cilia - 9 × 3
microtubules
Role in cell division - makes spindle that moves chromosomes
Cilia
• For movement of whole organism (e.g. Paramecium), or of material over the surface of the cell (e.g. mucus in respiratory tract)
• More complex structure than microvilli (fingerlike folds in the membrane to increase surface area
• Have microtubules running along length (9+2)
• Attached by basal body in cytoplasm (9 x 3 microtubules)
Flagella
Are tail like projections from a cell used in motility (movement )
Animal flagella
Animal lagella, also called undulipodia, are structurally the same as cilla, but much longer.
Most animal cells do not have undulipodia, but they are found in sperm cells.
Prokaryotic flagella
Prokaryotic flagella are thinner than eukaryotic ones and do not have the 9+2 arrangement of microtubule. The long filament of the flagellum is attached to the membrane of the cell by a hook section and rotated by a molecular motor. The molecular motor causes the filament of the flagellum to move in a whip-like fashion, propelling the cell. Some bacteria have multiple flagella
Prokaryotic cell
Key features
Prokaryotic cells (bacteria and archaea) do not have nuclei, and have no membrane-bound organelles. They have smaller ribosomes than eukaryotic cells (18nm / 70s). DNA is in a single circular chromosome of naked DNA (i.e. with no associated histone proteins), found in an area of the cell called the nucleoid. Prokaryotic cells can also have small, additional loops of DNA called plasmids. As well as being enclosed by a plasma membrane, prokaryotic cells have a cell wall made of peptidoglycan, and can be surrounded by a capsule
Eukaryotic vs prokaryote
size
Eukaryotic ->5 - 250 um
prokaryotic ->0.1 -10Mm
-Membrane bound organelles-
eukaryotic -multiple, complex Eg mulens, RER, Golge, lysomes, mitochandia
Eukaryotic ->-no membrare bound organelles
Dna -
Eukaryotic ->arranged in the nucleus in linear chromosome
-coiled around his one proteins to form chromatin
Prokaryotic-named DNA not assoscated with proteins
-single circular chromosomes
Ribosomes
larger - 22 nm
protocists
smaller - 18-20nm
Cell wall
Eukaryotic -> in plant cells and some protists
→ made of celilose in fungi
Prokaryotic -> sometimes present completely different structure to eukaryotic flagella made of protein flaggela
Cytoskeleton
made of microtubles and microfiliaments
Prokaryotic- present but very different in structure
Protein production and division of labour within a cell
1- the dna in the nucleus will carry the code for the hormone
2- a length of dna that codes for 1 protein eg one hormone is known as a gene and found on a length of dna known as a chromosome
3- a copy of the relevant length of DNA is made by the nucleus and this molecule is known as mRNA
4- mRNA leaves the nucleus through nuclear pore and attaches itself to a ribosome
5- if the protein is going to be exported from the cell as in the case of this hormone the ribosome is attached to the RER
6- the ribosome reads the code and assembles the correct amino acids to build the protein
7- the assembled proteins is then pinched off into a transport vesicle and transported to the Golgi apparatus
8- in the Golgi body the protein is modified (eg having non - protein groups added) and is then placed in a secretary vesicle
9- the protein in the secretary vesicle is transported to the plasma membrane.the vesicle fuses with the plasma membrane, releasing the protein by exothyosis (this is also known as secretion)
