Cells and organelles Flashcards
Structure of plasma membrane
-phospholipid bilayer
Function of plasma membrane
-defines the boundary of cell
-regulates entry and exit of chemicals
Structure of cytosol
-aqueous environment within the plasma membrane
Function of cytosol
N/A
Structure of cytoplasm
-cytosol plus organelles
Function of cytoplasm
N/A
Structure of cytoskeleton
consists of three types of protein polymers:
-actin filaments
-microtubules (tubulin)
-intermediate fibres
Function of cytoskeleton
-mechanical strength of cell
-control of shape
-facilitation of movement
-guide movement within cells
-interaction with other cells
Structure of nucleus
-surrounded by nuclear membrane
-largest organelle
-visible by light microscopy size: 3-10μm
Function of nucleus
-storage of chromosomes
-site of DNA replication
-site of gene expression
Structure of nucleolus
-region of nucleus
Function of nucleolus
-site of rRNA synthesis and ribosome biogenesis
Structure of nuclear membrane/envelope
-double phospholipid bilayer (inner and outer nuclear membrane
-perinuclear space between bilayers
-nuclear lamina is protein layer underneath the inner nuclear membrane
Function of nuclear membrane/envelope
-regulates the entrance and exit of mRNA and proteins
-maintains the integrity of the nucleus
Structure of mitochondria
-surrounded by membrane
-also second inner membrane that is folded into cristae that increases its surface area
-only visible by EM; size 0.5-2μm long
-number per cell reflects metabolic activity
-contains DNA that encodes ~1% of the mitochondrial specific proteins
Function of mitochondria
-aerobic oxidation of glucose to generate ATP (Krebs cycle)
-components of Electron Transport Chain are located in the inner membrane
-involved in oxidation of fatty acids
-involved in gluconeogenesis
-involved in regulated intrinsic apoptotic pathway
Structure of RER
-membrane bilayer surrounded endosomes
-membrane and inner space (lumen) continuous from the outer nuclear membrane
Function of RER
-coated with ribosomes
-mRNA translation and synthesis of proteins for secretion or insertion into cell membrane
-proteins are folded; Cys-Cys bridges form
-vesicles are budded from RER and transported to the Golgi body
Structure of SER
-membrane bilayer surrounded endosomes
-continuation of RER
Function of SER
-biosynthesis of membrane lipids and steroids
-start of N-linked glycosylation
-detoxification of xenobiotics (e.g. P450 system)
Structure of ribosome
Protein – rRNA complex
Function of ribosome
-assembly responsible for the translation of mRNA and the synthesis of proteins
Structure of Golgi body
-consists of 4-8 closely stacked, membrane-bound channels (cisterna)
-protein containing vesicles delivered from the RER
Function of Golgi body
-directs new proteins within vesicles to their correct location in cell
-transport of membrane lipids around cell
-creates lysosomes
-site of glycosylation modifications (modifying N-linked carbohydrates, glycosylation of O-linked carbohydrates and lipids)
-synthesis/packaging materials to be secreted
Structure of secretory vesicles
-membrane bound spheres
Function of secretory vesicles
-bud off from the Golgi
-vesicles fuse with inner surface of the plasma membrane and release their contents (exocytosis)
Structure of lysosome
-membrane bilayer surrounded vesicle; size 0.2-0.5µm
-contains >50 hydrolytic enzymes for all major cellular macromolecules
-inside is ~ pH 5.0.
Function of lysosome
-involved in organelle turnover/replacement – autophagy
-lysosome fuses with other organelles
-low pH is maintained by ATPase proton pump.
Structure of peroxisome
-surrounded by membranes
-only visible by EM: not very electron dense; 0.5-1.5μm
Function of peroxisome
-detoxification
-phospholipid synthesis e.g. plasmalogens
-oxidation of Very Long Chain Fatty Acids (VLCFA)
-contains enzymes which generate (and degrade) H2O2
Structure of Cilia
-hair-like extension of the plasma membrane
-contains a central core of modified tubulin
Function of cilia
-different types of cilia:
(i) sensing movement of fluid
(ii) moving liquid
(iii) detection of sound
Structure of extracellular matrix (ECM)
-protein and carbohydrate supporting network outside of cells
-this is not an organelle
Function of extracellular matrix (ECM)
-mechanical support for cells/tissues
Definition of prokaryote
Single-celled organism in which the chromosome is a circular strand lying free in the cell (i.e. no nucleus) and has no membranous organelles e.g. Bacteria
Defintion of eukaryote
One or more cells in which chromosomes are enclosed in a nucleus; typically have cytoplasmic, membrane-bound organelles, DNA divided into a series of linear chromosomes, and considerable differences occur between cells within the same organism. All complex organisms (plants, fungi, animals, protozoa, algae) are eukaryotes
Definition of virus
Assemblage of nucleic acid (DNA or RNA) and proteins (and often other molecules) which is parasitic on prokaryotes/eukaryotes. Viruses invade cells, subvert their protein synthesis machinery to make more viruses instead of normal cell proteins, then escape to infect other cells. Viruses are not cells or organisms in the strict sense (lack a plasma membrane and only operate chemically within host cells).
Definition of cell
Semi-independent, living unit within the body, (in unicellular organisms, completely independent) in which are sited the mechanisms for metabolism, growth and replication (by division). It consists of an aqueous solution of organic molecules surrounded by a membrane
Definition of organelle
Subunit within a cell, with a defined structure and performing specific, integrated activities. Some are bounded by membranes, others are non-membranous e.g. ribosomes
Definition of tissue
Organised assembly of cells and their extracellular products which carry out similar and coordinated activities within the body (connective, lymphoid)
Definition of organ
Assembly of tissues coordinated to perform specific functions within the body (eye, ear, heart, lungs, liver)
Definition of system
Assembly of organs with 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 the normal range of cell volume?
1000 - 5000um^3
Exceptions:
-erythrocyte (100um^3)
-oocyte (4000000um^3)
What limits the size of cells?
Rate of diffusion:
-movement of metabolites within cell
-uptake of oxygen from outside cell
-movement of mRNA from nucleus
-movement of vesicles inside cell
Solutions to cell size limitation
-Cytoskeleton to actively move things around cells
-Creation of giant cells with multiple nuclei so gene expression can occur in multiple places
-Gap junctions between cells for efficient movement of metabolites
What can light microscope see?
-Only nucleus and plasma membrane
Features of electron microscopy
-Sample preparation is highly artificial
-Cells are dead, fixed and dehydrated
Range resolvable by eye, light microscope and electron microscope
Eye: 0.2mm
Light: 10mm - 200nm
Electron: 10mm-0.1nm
