Histology - Anatomy of the Cell Flashcards
What % of the cell is water?
80% average (75-85% range)
What % of the cell is protein?
15% average (10-20% range)
What % of the cell is lipid?
2.5% average (2-3% range)
What % of the cell is carbohydrate?
1.5% average
What % of the cell is inorganic?
1% average
Do embryonic or old cells have more water?
Embryonic
What features are common to all eukaryotes?
An outer membrane, an inner cytosol, a cytoskeleton, membrane bound organelles in the cytosol and inclusions
What is the inner cytosol?
A solution of proteins, electrolytes and carbohydrates. Has both fluid and gel-like properties
What is the function of the cytoskeleton?
Determines shape and fluidity of the cell
What is the cytoskeleton made of?
Thin and intermediate filaments and microtubules
What are inclusions?
Structures within the cytoplasm which may or may not be membrane bound - they are dispensable and may be present only as transients
What is the plasmalemma?
A bimolecular layer of amphipathic phosphoric molecules with the ability to exocytose and endocytose material through it
What is the role of the plasmalemma?
To separate the cytoplasm from the outside environment
What proteins are in the plasmalemma?
Integral - receptors, channels, transporters, enzymes and cell attachment proteins and peripheral.
Why are proteins not distributed equally in the cell membrane?
Some diffuse laterally into the membrane but some are anchored
What is the membrane highly permeable to?
Water, oxygen, small hydrophobic molecules
What is the membrane virtually impermeable to?
Charged ions
Other than proteins what else in embedded in the plasmalemma?
Cholesterol
What are organelles?
Small, intracellular ‘organs’ with a specific function and structural organisation. They are essential to life
What is the role of mitochondria?
Generation of ATP (via oxidative phosphorylation) and the synthesis of certain lipids and proteins
What is the role of the rough endoplasmic reticulum?
Protein synthesis
What is the role of the smooth endoplasmic reticulum?
Cholesterol and lipid synthesis/detoxification
What is the role of Golgi apparatus?
Modification and packaging of secretions
What is the role of lysosomes?
Hydrolytic enzymes for cellular digestion
What is the role of the nucleus?
Contains the genetic code
Where can inclusions come from?
Can be synthesised by the cell (pigment, glycogen stores, lipid droplets, presecretion product) or can be taken up from the environment (endocytotic vesicle)
What are the 3 main classes of filaments?
Microfilaments, intermediate filaments and microtubules
What is the structure of microfilaments?
7nm, and composed of fine strands of actin (which can later dissociate = very dynamic)
What is the structure of intermediate filaments?
> 10nm, composed of 6 main proteins which vary dependent on cell type
What is the structure of microtubules?
25nm, hollow tubule composed of two types of tubular subunits - alpha and beta (in an alternating array)
How do filaments attach?
Anchoring and joining proteins to form a dynamic 3D internal scaffolding in the cell = cytoskeleton
What is the function of intermediate filaments?
To bind intracellular elements together and to the plasmalemma
What are types of intermit filaments at their location?
Neurofilaments - nerve cells Glial fibrillary acidic protein - glial cells in nervous system Desmin - muscle cells Cytokeratins - epithelial cells Vimentin - mesenchymal cells Filesin - lens of the ye Laminators - nuclei of all cells
Where do microtubules originate from?
Centrosome (special organising centre)
What types of protein do microtubules contain?
Stablising proteins - microtubule-associated proteins (MAPS)
Where do microtubules polymerise?
The central portion of the cell and radiate outwards = polar (this is important in cilia, flagella and the mitotic spindle)
What two proteins attach to microtubules to move them along?
Dyenin and kinesin by associating with membranes of organelles and vesicles and ‘dragging’ them along the microtubule
What is kinesin?
An ATPase that moves towards the cell periphery
What is dynein?
An ATPase that moves towards the cell centre
What organelle is at the core of centrosomes?
A pair of centrioles mainly composed of specialised microtubule segments
What encloses the nucleus?
A nuclear envelope - composed of an inner and outer membrane with pores (gives continuity in the cytoplasm)
What is found between the nucleus and the nuclear envelope?
The perinuclear cistern - continuous with the cistern of the endoplasmic reticulum
What studs the outer nuclear membrane?
Ribosomes and is continuous with the cytoplasms RER
Where are mRNA and tRNA transcribed?
Nucleus
Where is rRNA transcribed?
Nucleolus - a small dense area within the nucleus
What 2 types of DNA does the nucleus contain?
Euchromatin (more dispersed and actively undergoing transcription) and Heterochromatin (highly condensed and not undergoing transcription)
Where are ribosomes formed?
Nucleolus
What are ribosomes composed of?
A small subunit which binds RNA and a large subunit which catalyses formation of peptide bonds
What is the export of ribosomes dependent on?
The nuclear pore complex
What does the endoplasmic reticulum form?
A network of interconnecting membrane-bound compartments in the cell
Why is RER ‘rough’?
Studded with ribosomes
Where does RER play a vital role?
The synthesis of proteins defined for insertion into membranes or secretion
How does amount go ER in the cell affect how active the cell is?
Little ER = low metabolic activity
What is synthesised on polysomes?
Proteins that are to remain unpackaged in the cytosol
What is protein synthesis in relation to RER?
Free ribosomes attach to mRNA. If ER signal peptide sequence is present the growing peptide is inserted into a pore in the ER. The growing peptide forms in the ER and then the signal sequence is removed. Ribosome detaches and most completed proteins then enter the SER
What is the role of SER?
Continue processing the proteins produced in the RER
What is the Golgi apparatus composed of?
A group of flattened, membrane bound cistern arranged in sub-compartments
Where do transport vesicles from SER/RER go?
Golgi apparatus
How does the Golgi apparatus modify/package macromolecules?
Adds sugars, cleaves some proteins and sorts macromolecules into vesicles
What is the structure of mitochondria?
Outer and inner membrane, the inner is folded extensively to form cristae (inverses surface area).
What are the 3 types of intercellular junctions?
Occluding, anchoring and communicating junctions
What do occluding junctions do?
Prevent diffusion by linking cells - appear as a focal region of close apposition between adjacent cell membranes (also known as tight junctions to zonula occludens)
What do anchoring junctions do?
Link submembrane actin bundles of adjacent cells to provide mechanical strength (also known as adherent junctions or zonula adherent)
What do demosomes do?
Link submembrane intermediate filaments of adjacent cells (macula adherent) - common in skin
What is a junctional complex?
The close association of several types of junctions found in certain epithelial tissues
What do communicating junctions do?
Allow selective diffusion of molecules between adjacent cells (often termed gap junctions). Each junction is a circular patch with several hundred pores produced by connexon proteins - found in epithelia but also smooth and cardiac muscle for spread of excitation
How can material move across the membrane?
Diffusion, transport proteins (pumps/channels) or incorporation into vesicles (vesicular transport)
What are the 2 types of vesicular transport?
Endocytosis and phagocytosis
What is endocytosis?
Material from the extracellular space is incorporated into the cell. The membrane invaginates, fuses and the new endocytotic vesicle (endoscope) buds into the cell - often receptor mediated. (reverse in exocytosis)
What is phagocytosis?
Bacteria or larger particulate material is incorporated into the cell by phagocytosis. Bacterium binds to cell surface receptors triggering extensions of the cell to engulf it = phagosome. Phagosome binds with lysosome carrying digestive enzymes = phagolysosome
