Nucleus: controls transcription of DNA, therefore, production of proteins
Nucleolus: makes ribosomes
Nuclear pore: allows passages of substances, e.g., mRNA can leave
Lysosome
→ Membrane bound circular organelle with no clear internal structure
Function:
1. Contains digestive enzymes that break down invading foreign cells, e.g., pathogens
2. Simply worn-out parts of the cell
Ribosome
→ small organelles with no plasma membrane. Can be found freely in the cytoplasm or attached to rough endoplasmic reticulum
Function:
1. Where protein synthesis occurs
Rough Endoplasmic Reticulum (RER)
→ Fluid filled membrane bound sacs. Ribosomes attached to the surface
Function:
Folds + processes new proteins
Smoot Endoplasmic Reticulum (SER)
→ Like rough ER in terms of structure but has no ribosomes
Function:
1. Synthesizes and processes lipids
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Golgi apparatus
→ Also, fluid filled membrane sacs, often seen with vesicles nearby
Function:
1. Further processes the proteins
2. Packages proteins + newly synthesized lipids
3. Synthesizes lysosomes
Centriole
→ Mostly found in animal cells
Structure:
Made up of hollow tubules called microtubules (tiny protein cylinders)
Function:
Separating chromosomes during cell division
Mitochondrion
Structure:
• Double membrane, inner membrane is folded to form cristae.
• Inside is the matrix
• Where enzymes needed for respiration are found
Function:
1. To produce ATP in respiration
→ releases energy
3.3. ROUGH E.R AND GOLGI APPARATUS
Protein production & transport
Free ribosomes → make proteins that remain within the cell (intracellular proteins)
Ribosomes bound to rER → make proteins that leave the cell / become embedded in the plasma membrane (e.g., digestive enzymes + CFTR
protein)
Process
1) The rough endoplasmic reticulum helps to fold and process the proteins made
on the attached ribosomes.
e.g., a sugar chain may be added to form a glycoprotein
2) The Golgi apparatus further processes the protein
e.g., trimming the sugar chain or adding another sugar chain
It is then packaged into a vesicle ready for transport to the cell membrane or out of the
cell – exocytosis
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3.4. & 3.5. PROKARYOTIC CELLS
Structure of a prokaryotic cell
Components of a prokaryotic cell
1) Plasma membrane
• Similar to eukaryotic membrane
Made mostly of...
1. Proteins
2. Lipids
2) Cell wall
Made of...
1. Murein (a glycoprotein)
3) Pili
Some prokaryotic cells have them
Function:
1. Transfer genetic material to other cells
2. Help stick cells together
4) Slime capsule
Present in some e.g., bacteria cells
Function:
1. Help defend against attack from immune system
5) Mesosome
It is a folding of the cell membrane inwards
Debated whether...
1. It occurs for cellular processes
Or
2. It is an artefact that happens when the cell is handled to be placed on a microscope slide
6) Ring of DNA (plasmid)
• Separate section of genetic material that → can be transferred from one cell to another
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7) Coiled strand of circular DNA
→ Free floating in the cytoplasm: not membrane bound
8) Flagellum
Not present in all cells, and others have more than 1
Function:
1. Movement
9) Cytoplasm
→ No membrane bound organelles, do have ribosomes (much smaller than in eukaryotic cells)
Under an electron microscope
3.6. & 3.7. GAMETES AND FERTILISATION
The mitotic index
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑒𝑙𝑙𝑠 𝑤𝑖𝑡ℎ 𝑣𝑖𝑠𝑖𝑏𝑙𝑒 𝑐ℎ𝑟𝑜𝑚𝑜𝑠𝑜𝑚𝑒𝑠 Because when cells divide,
𝒎𝒊𝒕𝒐𝒕𝒊𝒄 𝒊𝒏𝒅𝒆𝒙 = the chromosomes
𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑒𝑙𝑙𝑠 𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑
condense and become
fatter
Tells you how many cells proportionally are dividing in a sample
How is it useful? – in checking for cancers, because cancer leads to a faster rate of cell division
Structure of gametes
Egg cells
- They are much larger than sperm cells
- They contain huge food reserves to nourish the embryo
5
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