2.1.4 - Eukaryotic cells 2 Flashcards
define the endoplasmic reticulum
3D network of membrane-bound cavities in the cytoplasm that links the nuclear membrane and makes up a large part of the cellular transport system (and synthesis of many different chemicals)
what are ribosomes made of?
ribosomal RNA and protein
- has a large and small subunit
what are the main type of ribosomes found in eukaryotic cells?
80s ribosomes
- 60s as the large subunit
- 40s as the small subunit
ratio of RNA : protein = 1: 1
What are the main type of ribosomes found in prokaryotic cells?
70s ribosomes
- 30s small subunit
- 50s large subunit
ratio of RNA : protein = 2:1
Other than prokaryotic cells, where are 70s ribosomes found?
- mitochondria of eukaryotic cells
- chloroplast of plant cells
Why do 70s ribosomes provide evidence for the endosymbiotic theory?
- 70s are reproduced independently in the mitochondria and chloroplast when a cell divides
- evidence that both of them evolved from bacteria
- caught inside eukaryotic cells very early in the process of evolution
- 70s ribosomes usually found in prokaryotic cells
define 80s ribosomes
main type of ribosome found in eukaryotic cells consisting of ribosomal RNA and protein (60s and 40s subunit) and are the site of protein synthesis
define 70s ribosomes
found in mitochondria and chloroplast of eukaryotic cells and in prokaryotic organisms
define rough endoplasmic reticulum (RER)
endoplasmic reticulum that is covered in 80s ribosomes and is involved in the production and transport of proteins
define exocytosis
the energy-requiring process by which a vesicle fuses with the cell surface membrane so the contents are released to the outside of the cell.
What are the roles of RER and 80s ribosomes in the production of proteins?
- 80s ribosomes makes the proteins
- RER isolates and transports the proteins once they have been made
- exocytosis is used to secrete proteins outside the cell without it interfering with the cell’s activities
What allows the RER to synthesise many proteins?
- a large surface area
what is special about the RER in the gut?
- it has large surface area
- as it produces digestive enzymes
- these are needed within the gut so a large surface area means a lot can be made
define smooth endoplasmic reticulum
smooth tubular structure similar to RER but without the ribosomes, it is involved in the synthesis and transport of steroids and lipids in the cell
where can you find lots of SER?
- testes, makes the steroid hormone testosterone
- liver, it metabolises cholesterol amongst other lipids
- amount and type of ER will give an idea of the type of job the cell does
define the golgi apparatus
stacks of membranes that modify proteins made elsewhere in the cell and package them into vesicles for transport (also produce materials for plant cell walls and insect cuticles) - lined with SER
what are cisternae?
the stacks of parallel, flattened membrane in the golgi apparatus
how are cisternae formed?
by the fusing of vesicles from RER
How do the RER and the golgi apparatus work together?
- proteins brought to the golgi apparatus in vesicles that are pinched off from the RER where they are made
- vesicles fuse with membrane sacs of golgi apparatus and the protein enters the golgi stacks
- proteins travel through the golgi and are modified
define a lysosome
an organelle full of digestive enzymes used to break down worn out cells/ organelles or digest food in simple organisms
What part of the golgi apparatus is very rich in enzymes?
- the inner areas
- nearer the RER
- where most enzymes/ membrane proteins are converted into the finished product
What part of the golgi apparatus is not very rich in enzymes?
- the outer regions
- you will find the finished protein products
- therefore not many of the enzymes that make them
how do proteins get to the outside of the cell from the golgi apparatus?
- vesicles containing secretions pinched off the golgi apparatus
- these vesicles then fuse with the cell surface membrane and release the secretions to the outside of the cell
what does ‘lysis’ mean?
- breaking down
where are lysosomes found?
in the cytoplasm of most cells
what do lysosomes look like?
- dark spherical bodies
what do lysosomes contain?
- powerful mic of digestive enzymes
what is the function of a lysosome?
- to break down/ destroy organelles in the cells of your body that are worn out
describe the process of a lysosome breaking down an organelle.
- fuse with each other
- enzymes break down contents into molecules that can be reused
- lysosome can fuse with outer cell membrane to release its enzymes outside the cell as extracellular enzymes (e.g to destroy bacteria)
define apoptosis
programmed cell death - the breakdown of worn out, damaged or diseased cells by the lysosomes
- they rupture to release their enzymes in the cell and destroy the contents