Cells and Organelles Flashcards
What is a Cell?
- semi-independent, living unit within the body (in unicellular organisms, completely independent)
- sited the mechanisms for metabolism, growth and replication (by division).
What is an organelle?
- subunit (functional unit) within a cell
- defined structure
- performing specific, integrated activities.
What is a Tissue (and 2 e.g.s)?
- organised assembly of cells and their extracellular products (what those cells secrete)
- carry out similar and coordinated activities within the body
- (connective, lymphoid)
What is a Organ (and e.g.s)?
- assembly of tissues
- coordinated to perform specific functions within the body (eye, ear, heart, lungs, liver)
What is a System (and 2 e.g.s)?
- assembly of organs
- specific, related activities
- sharing regulatory influences (e.g. respiratory).
- OR it may be a diffuse functional network of cells situated in many parts of the body
- sharing specific activities (e.g. immune)
What is a Prokaryote?
- single-celled organism
- chromosome is a circular strand lying free in the cell - - (i.e. no nucleus)
What is a Eukaryote?
- one or more cells
- chromosomes are enclosed in a nucleus
What is a Virus?
- an assemblage of nucleic acid (DNA or RNA)
- and proteins (and often other molecules)
- parasitic on prokaryotes/eukaryotes.
What is Cell Theory?
- “All living things are made of cells and these arise through the division of pre-existing cells”
- all present day cells evolved from same ancestral cell.
How do cells vary and how are they the same?
- Cells vary in shape, chem requirements and function
- all cells are rel the same size explained by fick’s law.
At what distance is diffusion efficient in a cell?
- Less than 50micrometers
- its red above 50
How do cells reproduce?
- replicating its DNA
- div in 2
- passing a copy of its gen instructions encoded in its DNA to each of its daughter cells
Why do distances within the cell have to be the same?
- Distance from nucleus to cell edge influences movement of intermediates, waste products and nutrients.
- as lots of diffusion in cell - this allows diffusion to occur efficiently or part of cell won’t get O2
How do specialised cells overcome this problem of diffusion? (Thin processes)
- cells are long and thin so distance of things diffusing in and out and in any part of the cell with the outside remains the same
– Directed transport of substances around cell via cytoskeleton e.g. neurones and oligodendrocytes
How do specialised cells overcome this problem of diffusion? (“Giant” multinucleate cells)
- If u need to proteins to be made and there’s only one nucleus, there’s a limit to how far the messages are carried around the cell
– Gene expression can occur in more than one place in the cell e.g. skeletal muscle cells
How do specialised cells overcome this problem of diffusion? (Gap juctions)
- Channels between cells e.g. Epithelial to allow movement of substances
- e.g. In an env where O2 can’t get access to a cell - Oxygen from one cell to the next can go through
Why is division of labour good?
- Multicellular org - allows some cells to become spec to extreme degree for certain tasks
- these cells dependent on other cells for basic requirements
Which type of microscope best reveals subcellular details and why?
EM - highest mag + best resolution
What is a Transmission EM used for and how?
to look inside a cell (electrons go through the specimen)
What is a Scanning EM used for and how?
to see the cell surface (electrons scattered off cell surface by heavy metal coating e.g. Au)
What prep is needed for EM?
- Cut v. thin sections,
- aq env removed,
- samples fixed (preserved by pickling in reactive chem sol)
What must the sample be like for EM?
Dead cells not living, wet cells
What is a difference between some organelles?
some mem-bound, others not e.g. ribosomes
What does the mem around some organelles allow? (4)
- Spec env to exist within it
- Diff spec functions in cell can op under diff cond e.g. pH
- Single cell can have numerous diff functional compartments
- Acts as phys barrier + can reg what crosses it + diff process + differentiate between them in cell
What are some features of eukaryotic cells in terms of:
- organelles
- chromosomes
- cells within same org
- types of organisms cells are found in
- size compared to pro
- typically have cytoplasmic, membrane-bound organelles
- DNA divided into a series of linear chromosomes
- considerable differences occur between cells within the same organism.
- All complex organisms (plants, fungi, animals, protozoa, algae) are eukaryotes but some single-celled e.g. amoebae + yeasts
- bigger than pro
What are some features of prokaryotes in terms of: (5)
- organelles
- example
- shape
- size
- extra feature it has eu doesn’t
- Has no membranous organelles
- e.g. Bacteria - Many diseases caused by them
- spherical, rod-like/corkscrew-shaped
- small - 1 micrometer
- cell wall surrounding plasma mem enclosing cytoplasm + DNA
Compare form and location of genetic material in both pro + eu
Pro: - form: in single circ chromosomes - location: in nucleiod Eu: - form: in paired chromosomes - location: in nucleus
Compare location of extrachromosomal DNA in pro + eu
Pro: - in plasmids Eu: - in mit - plasmids
Compare plasma + internal mem in pro + eu
Pro: - plasma mem: lacks sterols, - internal mem: only in photosyn org Eu: - plasma mem: contains sterols - internal mem: many mem-bound org
Compare location of resp in pro + eu
Pro:
- at cell mem
Eu:
- in mit
Compare cell wall + external layer in pro + eu
Pro:
- cell wall: peptidoglycan, LDS + teichoic acid
- external layer: capsule/slime layer
Eu:
- cell wall: none in most but chitin in fungal cells
- external layer: none in most but pellicle/shell in some parasites
Compare presence of cilia, pili + flagella in pro + eu
Pro: - cilia absent, - pili present, - flagella present Eu: - cilia present in some - pili absent, - flagella present in some
Compare cell division + reproduction mode in pro + eu
Pro: - cell div: binary fission - rep mode: asexual Eu: - cell div: mitosis/meiosis - rep mode: sexual/asexual
Compare size of ribosomes in pro + eu
Pro: - 70s Eu: - 80s in cytoplasm + RER, - 70s in mit
How do viruses operate?
- invade cells,
- subvert their protein synthesis machinery to make more viruses instead of normal cell proteins,
- then escape to infect other cells.
Why are viruses not cells/org/pro?
- not cells/organisms - lack a plasma membrane and only operate chemically within host cells.
- Not prokaryote - can’t function without host - not free living. No ability to reproduce themselves
Put in order of decreasing size: animal cell, virus, bacterial cell
Animal cell (10-100micrometres), bacterial cell (1 micrometre), virus (50nm)
What is cytoplasm?
cytosol + organelles
What is cytosol?
- aqueous environment within the plasma membrane
- part of cytoplasm not contained in within intracellular mem
- water-based gel, protein rich fluid
- site of many chem reactions fundamental to cell’s existence
What is the nucleus structure in terms of:
- size
- vis by LM
- DNA
- Largest organelle in the cell (diam. 3-10μm, 80-800 nm)
- Only organelle clearly visible by light microscopy
- DNA winds round histones into nucleosomes
– “naked” human DNA : 1.8m
– DNA packaged in nucleosomes: 95mm
– further condensed in mitosis as chromosomes: 120μm
– Unless cell is dividing chromatin is decondensed
What is chromatin?
complex of DNA/histone and non-histone proteins
What is nucleolus?
- Site of rRNA genes transcription
- where rDNA is transcribed and ribosome subunits assembled
What is nuclear envelope structure and function?
- two layers of membrane enclosing nucleus
- allows protection of nuclear DNA, control of pH in that region
What is a nuclear pore?
- hole in nuclear envelope
- allows transport in and out nucleolus - e.g. mRNA can enter into cytoplasm
What is the Plasma mem?
- phospholipid bilayer where hydrophil heads face out + hydrophob fatty acid tails face in aq env
- mem is fluid - lateral diffusion (phos diffuse freely within each layer) + cholesterol
- cell surface proteins - glycosylated = sugars added - signalling, transport/structural functions
What is a lysosome structure and function?
- Electron-dense spheres (vesicles)
- diameter: 80-800nm
- contain acid hydrolase enz - catabolise macromol
– Lysosomal proteins are tagged with mannose -6- phosphate (sugar) - receptors recognise it and allow vesicles to be taken up by the lysosome - useful way of targeting proteins/vesicles within the cell
What is a peroxisome structure?
- small mem bound vesicles
– Large (0.5-1.5μm), not very electron-dense
What is SER?
- site of Biosynthesis of lipids, steroids;
- metabolise carbohydrates/steroid
- store intracellular Ca2+
What is RER structure and function?
- Irregular maze of interconnected spaces enclosed by mem
- Coated with ribosomes
– Proteins + mem are folded - max SA
What is Golgi body structure?
- 4-8 closely-stacked, membrane-bound channels
- (many stacks/mammalian cell)
What are secretory vesicles?
- small mem surrounded pockets
- bud off from the Golgi
- fuse with the inner surface of the plasma membrane and release their contents (exocytosis) e.g. hormones and neurotransmitters
What is endocytosis?
Portions of plasma mem tuck inward + pinch off to form vesicles that carry material into cell
What is nucleus function?
Contains genetic material that is packaged – DNA organised as chromosomes;
What is lysosome function?
- digest unwanted + defective proteins – (Protein, RNA and DNA degradation)
- recycle raw materials within cell from breakdown of unwanted mol/excrete from cell - prevent acc of waste
- release nutrients from ingested food particles
- work optimally at pH5 – Powerful enzymes that require low pH
What is peroxisome function?
- enz that gen + degrade H2O2
- provides safe env for Detoxification of proteins/chem - compartmentalised
– Phospholipid synthesis - mem form many diff types of small transport vesicles - carry materials between 1 mem-bound org + another
What is function of RER?
- translation of proteins mainly for secretion or insertion into cell membrane
– Vesicles = are budded from RER and transported to the Golgi body
What is Golgi body function?
• Modifies proteins delivered from RER e.g. by adding sugar (carbohydrate) or lipid (fat) side-chains (All proteins on cell surface covered with carbs and fats)
- Synthesise/package materials to be secreted out/transported within cell
• Direct new proteins to their correct compartments in vesicles - e.g. to mem, lysosomes etc
• Transport lipids around cell
• Create lysosomes
- trim aa side chains to right length, protein folding,
- identify improperly folded proteins tagged for destruction by lysosomes
What is a normal size for a virus?
50nm
What is smallest size resolvable by electron microscope?
0.2nm
What is the smallest size resolvable by light microscope?
200nm
What is a normal size for a bacterium?
1µm
Where are cells with dimensions larger than 50µm found?
nervous system
What is Myoclonic Epilepsy with Ragged Red Fibres (MERRF) syndrome cause and symptoms?
- Mutation of mit gene for tRNA-lys
- Disrupts syn of ox phos enz
Symptoms: - lactic acid acidosis,
- myoclonic seizures,
- weakness,
- un-coord etc
What is Hutchinson-Gilford Progeria (Human premature ageing syndrome) cause and symptoms?
- Mutation in lamin = part of nuclear envelope
- Distorted shape of nucleus (blebbed)
- production of unique progerin protein
Symptoms: - Extreme growth delay,
- skeletal dysplasia,
- thin skin etc
What is Tay Sachs disease cause and symptoms?
- Disease of lysosome
- mutation of lysosomal hexosaminidase
- Acc of gangliosidase - neurotoxic
Symptoms: - progressive paralysis,
- inc loss of vision,
- hearing loss,
- seizures etc
What is Zellweger Syndrome and cause?
- Inherited absence of peroxisomes
- Mutations in specific proteins in peroxisome
