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