Cells And Organelles Flashcards
List the major organelles/sub cellular structures of a typical human cell.
- plasma membrane
- nucleus
- cytoskeleton
- mitochondria
- free ribosomes
- Golgi apparatus
- endoplasmic reticulum
- rough endoplasmic reticulum
- lysosomes
- peroxisomes
- endosomes
Describe the structure of the plasma membrane of a typical human cell.
- phospholipid bilayer
- proteins dotted throughout (transmembranous and peripheral)
- cholesterol molecules
- carbohydrates
- amphipathic
- semi-permeable
- fluid mosaic model
What are the functions of the plasma membrane of a typical human cell?
- regulate entry and exit from the cell
- cell signalling
- support (attachment to ECM or cytoskeleton)
- site for enzyme activity
- form membrane for sub-cellular organelles
How does the plasma membrane interact with the extracellular environment?
- Through integral plasma membrane proteins:
- allow transfer of small molecules across the membrane
- through pumps, carriers, channels
- Through plasma membrane receptors:
- interact with a specific ligand
- initiate a cascade of chemical signals in the cell
Discuss the composition and function of the nucleus.
Composition:
- bound by a double membrane/nuclear envelope
- DNA packaged as chromatin
- nuclear pore facilitates entry and exit to nucleus
- membrane supported by nuclear lamina
- nucleolus
Function:
- nucleolus synthesises rRNA and ribosomes
- DNA replication (mRNA)
- gene expression (transcription/post-transcriptional modification)
Why is it important that the cell compartmentalises into different organelles?
- to provide a permissive environment for a set of biochemical functions
- to protect the cell by segregating destructive enzymes and chemicals
- to localise cellular processes for efficient functioning
- to separate molecules required for specific functions
Describe the structure of mitochondria.
Outer membrane:
- contains portions? (Proteins which allow movements of ions in and out of mitochondrion)
- also contains enzymes involved in elongation of fatty acids and oxidation of adrenaline
Inner membrane:
- folded into cristae to increase SA available for ATP production
- contains enzyme ATP synthase which generates ATP in matrix
- contains transport proteins that regulate movement of metabolites into and out of matrix
Inter membrane space:
- space between outer/inner membrane
Matrix:
- space within the inner membrane
- contains enzymes of Krebs and fatty acid cycles
- contains DNA, RNA, ribosomes and calcium granules
Discuss the function of mitochondria.
- ATP production
- store capsases which are responsible for triggering apoptosis (cytochrome C)
- transiently store calcium to contribute to calcium homeostasis
- abundant in the ovum for development and possibly in sperm for motility
Describe the structure and function of the endoplasmic reticulum.
Structure: - continuous with nuclear membrane - system of flattened sacs (cisternae) Function: - synthesis
Describe the structure and function of rough endoplasmic reticulum.
Structure:
- ribosomes attached to cytoplasmic surface
Function:
- takes developing proteins from cytosol and continues their development
- post-translational modifications
- proteins destined for ECM e.g. mucous and enzymes
- proteins associated with the cell membrane e.g. receptors and channels
- proteins for membrane bound vesicles e.g. enzymes of lysosomes
- protein folding
- abundant in plasma cells for production of immunoglobulins
Describe the structure and function of smooth endoplasmic reticulum.
Structure:
- does not contain ribosomes
- usually less extensive than rER except in some specialised tissues
- contains cytochrome P450 enzymes which are important in the metabolism of certain drugs and toxins e.g. alcohol an barbiturates
Function:
- synthesis of lipids, phospholipids and steroids
- calcium storage
- abundant in hepatocytes for lipid synthesis and Leydig cells for steroid hormone biosynthesis
What is the difference between rER and sER?
- rER has ribosomes attached, sER does not
- rER plays role in synthesis and folding of proteins
- sER synthesises lipids, phospholipids and steroids
Describe the structure and function of the Golgi apparatus
Structure:
- 5-8 folds called cisternae
- Cis-Golgi network faces the nucleus, forms a connection with ER and is the entry point to the Golgi
- cis/medial/trans-Golgi are the major processing areas that allow biochemical modifications
- trans-Golgi network is the exit point for vesicles budding off from Golgi surface (packaging and sorting)
Function:
- modifies proteins and lipids that it receives from ER
What is the address label for proteins bound for the lysosome?
Mannose-6-phosphate
What are lysosomes?
- vesicles containing hydrolytic enzymes
- have a low pH
- degrade defective/old organelles, macromolecules and particles taken in from outside the cell
What are endosomes?
- Hint - endo meaning in*
- vesicles involved in transport of molecules from plasma membrane to lysosome
What are peroxisomes?
- a compartment for enzymes involved in oxidative reactions
- also involved in the the biosynthesis of bile acids, fatty acid metabolism and detoxification
Discuss Tay-Sach’s disease.
- build of lipid in neuronal bodies and processes
- because of failure to degrade lipids
- causes neurological regression, seizures and blindness
- rare and usually fatal
- genetic
What are the functions of the cytoskeleton?
- to organise cell structure and maintain the correct shape of the cell
- to support fragile plasma membrane
- provide mechanical linkages to allow cell/tissue to bear stress
- allows cell to adopt specific behaviours (e.g. growth, division, migration, motility)
What types of filament are found in the cytoskeleton?
Microtubules: - composed of tubulin monomers Microfilaments: - composed of actin Intermediate filaments: - can be made up of keratin, vimentin, desmin and lamins
What are the motor proteins for Microtubules and microfilaments?
Microtubules - powered by dynein and kinesin
Microfilaments/action - powered by myosin
What forms the basis of cell projections? Give examples.
Actin Microfilaments
E.g. microvilli which increase SA for absorption in the gut
E.g. stereocilia that detect sound in the inner ear
Which filament forms a cortical network in the cytoplasm? What does it facilitate?
- actin
- cell contraction
- shape change
What filaments help to produce membrane extensions such as lamellipodia and filopodia?
- actin
- helps with cell motility
