Eukaryotic cell structure and function Flashcards
What is life
The state or quality that distinguishes living beings or organisms from inorganic matter
Metabolism
Response
Sensitivity
Growth
Reproduction
Excretion
Nutrition
What are cells
fundamental units of life
What defines a cell?
• Discrete, easily recognisable packages (cell membranes)
• made up of phospholipids which prevent the entry of hydrophilic compounts
What are the chemical properties of cells?
• all cells are similar inside
• they are composed of the same sort of molecules
• information flows from DNA via RNA to proteins
• proteins influence cell behaviour
What is the composition of cells?
• 70% water
• 30% varying chemicals and proportions of structural and functional molecules
Give physical properties of prokaryotic cells and examples
• eg spherical cells, rod shaped cells, spiral cells
• typically spherical, rod like or corkscrew shaped
• protective cell wall surrounding plasma membrane
• no organelles, circular DNA
• typically single celled, aerobic or anaerobic
What are the physical properties of eukaryotic cells?
• Larger and more complex than prokaryotes
• can be unicellular or part of multicellular organisms
• linear DNA molecules
• chromosomes in nucleus, chromosome number and ploidy widely variable
• membrane bound organelles
What are the functions of the plasma membrane
• Regulate transport (eg nutrients, waste)
• Maintain ‘proper’ chemical conditions
• Provide a site for chemical reactions unlikely to occur in aqueous environment
• Detect signals in the extracellular environment
• Interact with other cells or the extracellular matrix
Role of Nucleus
membrane bound structure, separates DNA from cytosol, transcription from translation (see genetics)
role of endoplasmic reticulum
RER: protein synthesis
SER: lipid and steroid synthesis
Ca2+ ion storage & detox
role of ribosomes
50% protein and 50% rRNA
used for protein synthesis, often associated w RER
role of golgi complex/apparatus
series of flattened discs called cisternae, modifies and sorts most ER products
role of mitochondria
Site of ATP production via aerobic metabolism, important role in apoptosis, self replicating (fission)
What are the properties of mitochondrial DNA?
• Mitochondria contains multiple mtDNA molecules
• genes in mtDNA exhibit cytoplasmic inheritance and encode rRNAs, tRNAs, and some mitochondrial proteins
• the size and coding capacity of mtDNA varies considerably in different organisms
• products of mitochondrial genes are not exported
• mutations in mtDNA cause several genetic diseases in humans
role of lysosomes
•degrade certain cell components, material internalised from the environment
• appear
as electron dense bodies on EM
• single membrane
• pH of lumen 3.5-5
• contains acid hydrolases
• if lysosomal enzyme is missing eg hydrolytic enzymes (generic defect): accumulation of material leads to lysosomal storage disease
role and features of peroxisomes
role:
• responsible for degrading:
- fatty acids eg oxidation of them
- toxic compounds eg alcohol oxidation
features:
- single membrane
- contain oxidases (eg urate oxidase and catalase)
- can be diverse in size and enzyme composition eg special plant peroxisomes
composition of cytoskeleton
3 major filamentous compounds:
• microtubules ~25nm (tubulin)
• actin filaments ~6nm (actin)
• intermediate filaments ~10nm (different subunit proteins)
role of cytoskeleton
• Essential in movement of cellular components and the cell itself
-maintains cell shape
-vesicular transport
-cell division
• Number of accessory proteins associated with with the filamentous components
function of actin
• maintains cell shape by resisting tension (pull)
• moves cells via muscle contraction or cell crawling
• divide animal cells into two
• move organelles and cytoplasm in plants, fungi, and animals
• cell shape and whole cell locomotion
• cells which need to move rich in actin
function of intermediate filaments
• maintain cell shape by resisting tension
• anchor nucleus and some other organelles
• rope like fibrous proteins (defined by size)
• abundant cytoplasmic and nuclear proteins
• provide structural reinforcement and stress resistance
function of microtubules
• maintain cell shape by resisting compression
• move cells via flagella or cilia
• move chromosomes during cell division
• assist formation of cell plate during plant cell division
• move organelles
• provide tracks for intracellular transport
• dynamic (end grows rapidly)
What are motor proteins
(not enough to have cytoskeleton)
• need motors to move vesicles
• three superfamilies identified with multiple members
• presence of conserved amino acids sequence, forms the ATP-binding and force-producing motor domain
What does the motor protein Myosin do
acts on actin- cell surface contractions- morphological changes- vesicle motility- muscle cell contractions
what does the motor protein Dynein and kinesin do?
Interact with microtubles to move vesicles and organelles, movement of flagella and cilia- essential in mitosis and meiosis in function of the spindle
What are the physical properties of myosin?
• expressed in virtually all eukaryotic cells
-couple hydrolysis of ATP to conformational changes
• head (motor domain)
- ATP and actin binding site
- exhibits actin activated ATPase activity
• Neck region
- an extended a helix
• Tail region
- effector domain
- determines specific function
What are the properties of Dynein and Kinesin?
• cytoplasmic motors:
- Dynein: large mass, higher complexity, activity can be dynamically regulated
- Kinesin: simpler structure, either active or inactive
• both move in one direction only
- dynein: moves towards - end of microtubule
- kinesin: move towards + end of microtubule
- force and movement generated by ATP hydrolysis
•involved in many processes (eg cell division, intracellular transport)
What mutations in the cytoskeletal components can lead to disease?
• actin mutations: congenital myopathy
• intermediate filament mutation: >30 human disease
• microtubule mutations/disfunction : neurodegeneration
How do we use cytoskeleton as a target?
•Pharmaceutical agents can be used to target cytoskeletal components
- eg polymerisation of filaments
- colchicine, causes microtubule depolymerisation, may contribute to its role in treating gout
•targeting cancer
- vinca alkaloids and paclitaxel disrupting cell cycle progression by inhibiting mitotic microtubules
• can also target assessory proteins, and ECM
- integrins are target for antiplatelet drugs
