Week 5 (organelles) Flashcards
What are organelles?
- discrete structures of a eukaryotic cell
- membrane enclosed
- carry out specialised functions - distributed throughout the cytoplasm
What is the difference between the cytoplasm and the cytosol?
Cytoplasm:
-cell contents (including organelles) within plasma membrane (except nucleus)
Cytosol:
-contains large and small molecules - concentrated aqueous gel around organelles - site of many chemical reactions
Describe the properties of the nucleus?
- most prominent organelle
- characteristic of eukaryotes
- contains the genome (chromosomes and protein)
- site of DNA and RNA synthesis - nuclear envelope surrounds nucleoplasm
When do chromosomes become visible?
Condense and become visible as a cell is about to divide
Describe the function and properties of the nucleolus
- site of ribosome production
- rRNA synthesis
- variable in size depending on number of ribosomes produced (Not membrane bound)
Describe the properties of the nuclear envelope
A double lipid bilayer (4 leaflets) with pores (filled with proteins) where inner and outer membranes connect
- envelope penetrated by pores
- act as gates to permit RNA proteins and other molecules to move appropriately)
- provides QC (only mature mRNA leave) ~1000 NPCs in a nuclear envelope of a vertebrate cell
What support is in the nucleus?
- supported mechanically by networks of intermediate filaments (outside)
- Inside the nuclear envelope= nuclear lamina (dense layer of microfilaments continuous with nuclear membrane
- Fibrous network surrounding the nucleus (cytoskeleton)
Do all eukaryotic cells contain a nucleus?
No E.g. erythrocytes
Do some eukaryotic cells have more than one nucleus?
Yes Skeletal muscle cells
Describe the properties of the endoplasmic reticulum
- massive membrane system
- interconnecting labyrinth of branches and flattened sacs
- contains over 50% of a cells membrane
- continuous with nuclear envelope
Describe the function of the rough endoplasmic reticulum
- central role in biosyntheis and modification of lipids and proteins e.g. adding sugar to make glycoproteins
- protein for:
export
some organelles
-proteins can move into the ER whilst being made
What is the difference between rough and smooth ER?
SER:
- ER without ribosomes
- Phospholipid synthesis
- Lots in hepatocytes (liver cells)
RER:
- ER with ribosomes
- Protein modification and secretion
- Lots in specialised secretory cells like plasma cells
Describe the properties and functions of the smooth ER?
- abundant in cells involved in lipid metabolism e.g. steroid hormone production from cholesterol
- often occurs within regions of RER (one connected system of membrane)
- involves in Ca2+ storage Involved in rapid cellular processes
Describe the properties and function of the Golgi apparatus
- Works closely with ER
- Made of flattened membrane bound sacs aka cisternae
Two sides and a middle:
- Entry side: ‘Cis’ Golgi (facing ER membrane)
- Middle: ‘Medial’ Golgi
- Exit side: ‘trans’ Golgi (facing plasma membrane)
Describe the function of the Golgi apparatus
- functions to process, pack and export protein and lipids in vesicles
- Lipids and protein enter at the cis side
- Progress through different levels of cisternae via transport vesicles
- different layers contain different enzymes that modify proteins
- Further sugar modifications occur here
- Packed in vesicles to be transported
Describe the properties of the mitochondria
- the site of energy generation (ATp production) in the cell
- independent genome (DNA), their own ribosomes, tRNA and they synthesise their own proteins: Although some proteins in mitochondria are self syntheised some come from the nucleus
- two membranes (outer and inner): -inner membrane is highly convoluted —> Cristae (large surface area)
- outer membrane is permeable to recieve things from the cytosol - site of generation of ATP
- Matrix inside the inner membrane
- resemble prokaryotic organism
Describe the properties of the lysosomes
- acidic organelles
- involved in degradation and recycling: (unwanted organelles-autophagy) phagocytosed things e.g. bacteria
- breaks things down to their building blocks some of which can be recycled and used again
- contains acid hydrolases a range of enzymes that only work at low pH (pH5) - proton pump and chloride channel maintains low pH H+ and Cl- enter lumen (inside) of lysosome acidic: H+ +Cl- —-> HCl
- single membrane
Where are SER abundant?
in cells involved in lipid metabolism e.g. steroid hormone production from cholesterol
What would happen if the lysosomal membrane got damaged and the enzymes leak out?
Cell would not get damaged because lysosomal enzymes only work at low pH
Can there be more than one nucleolus?
Yes Depending on the cellular needs (amount of protein synthesis)
What is the perinuclear splace?
Space between RER membrane and nuclear membrane
Does the Golgi apparatus use just one enzyme?
No
-A range of different enzymes are localised through the structure
what organelles are present in yeast?
- Nucleus
- Golgi apparatus
- mitochondria
- endoplasmic reticulum
- vacuole
- cytoskeleton
D
What is the difference between prokaryotic and eukaryotic cells?
