Cell Structure And Organisation Flashcards
The ribosome:
Very small organelles - 25 nm diameter
Present in large numbers
Found free in the cytoplasm of on the outer surface of the rough ER
made up of 2 subunits, one large, one small
Made up of ribosomal RNA and protein
Involved in protein synthesis
70s found in prokaryotes
80s found in eukaryotes
Manufactured in the nucleolus
Nucleolus:
2 micrometers
1/2 per nucleus
Synthesises ribosomal RNA and assemble the ribosomes from it
Spherical, darkly stained
Mitochondria:
0.5-10 micrometers
Site of aerobic respiration
Synthesises ATP
numbers may vary from 50-100
The highly folded inner membrane provides a large surface area for the respiration reactions. Some reactions also take place in the matrix.
There will be more in cells with high ATP requirements:
- cells that move a lot (sperm, muscles)
- cells which carry out active transport (small intestine)
- cells with high metabolic rate (lots of chemical reactions - liver)
- mitochondrial size and folding inner membrane may also be greater in these cells
Lysosomes:
Membrane bound vesicles which contain digestive enzymes
0.1-1.2 micrometers
Contribute a dismantling and recycling facility
They assist degrading material taken in from outside the cell and life expired components from within the cell e.g. Destruction of invading bacteria
Nucleus:
Largest organelle
20 micrometers diameter
Controls cells activities and retains the chromosomes
Contains chromatin, the material that condenses to form the chromosomes during cell division
Surrounded by a double membrane (nuclear envelope) which has pores to allow exchange with the cytoplasm (e.g. MRNA out, nucleotides in)
Chromatin:
Material chromosomes are made from
Condensed into chromosomes during cell division
Made of DNA and histone proteins, that it is wrapped around to be packaged
Endoplasmic reticulum:
An elaborate system of membrane bound sacs (cisternae), often continuous with the nuclear envelope and Golgi body
ROUGH
- has ribosomes lining it
- involved with protein synthesis as a transport system
SMOOTH
- lacks ribosomes
- involved with the synthesis and transport of lipids
Golgi body:
Similar to ER but has a more compact form
A collection of flattered membrane sacs that are constantly forming on one side and budding off as vesicles on the other
Forms lysosomes
Produces glycoproteins
Secretes carbohydrates
Packages proteins for secretion
Transports and store lipids
Plasmodesmata:
Small channels that directly connect the cytoplasm of neighbouring plant cells to each other, establishing living bridges between cells
Vacuole:
Animal cells contain small, temporary vacuoles and occur in large numbers
Plant cells have large permanent vacuoles which consist of fluid filled sac bounded by a single membrane, the tonoplast.
Contains cell sap, which provides osmotic system which functions in support of young tissues. It is also a storage site for chemicals such as glucose
Chloroplast:
Site of photosynthesis
Approx 3 micrometers wide, 6 in length
Centrioles:
Hollow cylinders 0.5 micrometers in diameter
At cell division they migrate to opposite poles of the cell where they synthesis the micro tubules of the spindles.
