Anatomy of Cell Flashcards
Describe the composition of each of the following components based on average, %range, and comment: water, protein, lipid, carbohydrate, and inorganic.
Water: 80%, 75-85%, 90% free/ 5% bound.
Protein: 15%, 10-20%
Lipid: 2.5%, 2-3%
Carbohydrate: 1.5%, ~1%
Inorganic: 1.0%, 1%
Describe the features common to all eukaryotic cells.
Outer membrane, inner cytosol (solution of proteins, carbohydrates, and electrolytes. It has both fluid and gel-like properties), cytoskeleton - determines the shape and fluidity of cell (made from thin and intermediate filaments and microtubules), membrane bound organelles within cytosol, other structures which may or may not be bound by a membrane - inclusions.
What is a plasma membrane?
Bimolecular layer of amphipathic phospholipid molecules with their hydrophilic heads at the outer and inner surfaces and their hydrophobic fatty acid chains facing towards the middle of the 2 layers.
What does the plasma membrane contain?
Integral proteins which the cell inserts into the membrane. These include receptors, channels, transporters, enzymes, and cell attachment proteins.
What ability does the cell have?
Exocytose and endocytose material through the cell membrane.
In what way do membrane proteins diffuse?
Laterally, but many are anchored, so it’s important to realise that many proteins are not distributed equally within the cell membrane.
What is the cell membrane permeable and impermeable to?
Highly permeable to: water, oxygen, and small hydrophobic molecules.
Virtually impermeable to charged ions (eg Na+).
On what basis can structures in the cytoplasm be identified under the microscope?
Size, shape, and staining reactions.
What are organelles?
Small, intracellular ‘organs’ with a specific function and structural organisation.
List examples of organelles.
Mitochondria, rough endoplasmic reticulum, smooth endoplasmic reticulum, Golgi apparatus, lysosomes, and the nucleus.
What are inclusions?
They are dispensable and may be present only as transients.
What do inclusions represent?
Components that have been synthesised by the cell itself (pigment, glycogen stores, lipid droplets, presecretion product) or taken up from the extracellular environment (endocytotic vesicle).
What are the 3 main classes of filaments?
Microfilaments (7nm in diameter) - composed of the protein actin, intermediate filaments (>10nm in diameter) - composed of 6 main proteins, which vary in different cell types, microtubules (25nm in diameter) - composed of 2 tubulin proteins.
What can actin molecules do?
Assemble into filaments and later dissociate, making them very dynamic cytoskeletal elements.
What is the function of intermediate filaments?
Bind intracellular elements together and to plasma membrane.
List the type of intermediate filament and its location/cell type.
Neurofilaments - nerve cells, glial fibrillary acidic protein - glial cells of nervous system, desmin, muscle cells, cytokeratins - epithelial cells, vimentin - mesenchymal cells, filesin - lens of the eye, lamin - nuclei of all cells.
What do intermediate filaments form?
A network throughout the cytoplasm.
What are microtubules?
Hollow tubule composed of 2 types of tubulin subunits, α & β in an alternating array. It can be assembled and disassembled.
Where do microtubules originate?
From a special organising centre called the centrosome. Include stabilizing proteins: microtubule-associated proteins (MAPS).
What is the microtubules important in?
Cilia, flagella, and the mitotic spindle.
What do microtubules serve as?
The ‘motorway’ network of the cell.
What are the two proteins that attach to the microtubules and move along them?
Dynein and kinesin.
What is the function of dynein and kinesin?
Kinesin is an ATPase that moves toward the cell periphery and dynein is an ATPase that moves toward the cell centre. These proteins are very important in the movement of components in cells with long processes, eg the very long axonal process of many neurons.
Describe the structure of the nucleus.
It is enclosed by a nuclear envelope, composed of an inner and an outer nuclear membrane with nuclear pores providing continuity with the cytoplasm. The outer nuclear membrane is studded with ribosomes and is continuous with the cytoplasmic rough endoplasmic reticulum.
What is the function of the nucleus?
Contains chromosomes and is the location of RNA synthesis. Both mRNA and tRNA are transcribed in the nucleus, and rRNA is transcribed in the nucleolus, a 1-3µm diameter dense area within the nucleus.
What does the nucleus contain?
Euchromatin (DNA that is more dispersed and is actively undergoing transcription), and heterochromatin (DNA that is highly condensed and not undergoing transcription).
Where are the ribosomes formed and what are they instrumental in?
The nucleolus and are instrumental in protein synthesis.
What are the ribosomes made from?
Each ribosome is made up of a small subunit - which binds RNA, and a large subunit which catalyses the formation of peptide bonds.
What does the export of ribosomes depend on?
The nuclear pore complex.
What is the endoplasmic reticulum?
The endoplasmic reticulum forms a network of interconnecting membrane-bound compartments in the cell. In micrographs, it appears as flattened membrane sheets or elongated tubular profiles.
What is the rough endoplasmic reticulum?
It is studded with ribosomes and plays a vital role in the synthesis of proteins destined for insertion into membranes or for secretion. It is also associated with glycoprotein formation.
What is the amount of ER present in the cell?
It varies with how active the cell is. Cells that are relatively metabolically inactive have relatively little ER.
What is the function of the smooth endoplasmic reticulum?
Continues the processing of proteins produced in the RER. The SER plays a vital role in the site of synthesis of lipids.
What is the amount of SER present in the cell?
Most cells contain relatively little SER, but in some (eg cells synthesizing steroid hormones) it is extensive.
What is the golgi apparatus?
Composed of a group of flattened, membrane bound cisternae. These are arranged in sub-compartments.
Describe the function of the golgi apparatus.
Transport vesicles arrive at the golgi from the SER/RER. Golgi cisterns function in the modification and packaging of macromolecules that were synthesised in the ER. It adds sugars, cleaves some proteins, and sorts macromolecules into vesicles.
What is the mitochondria?
Oblong, cylindrical organelles, typically 0.5-2µm in length. They are composed of an outer and an inner membrane. The inner membrane is extensively folded to form cristae, which act to increase the available surface area. They contain their own DNA and system for protein production.
What is the function of the mitochondria?
Power generators of the cell. They function in the generation of ATP, via oxidative phosphorylation, and in the synthesis of certain lipids and proteins.
What are intercellular junctions?
Specialized membrane structures which link individual cells together into a functional unit. They are particularly prominent in epithelia.
List the 3 types of junctions.
Occluding junctions - link cells to form a diffusion barrier, anchoring junctions - provide mechanical strength, communication junctions - allow movement of molecules between cells.
What are occluding junctions?
Appear as a focal region of close apposition between adjacent cell membranes. Are also known as tight junctions or zonula occludens. They prevent diffusion.
What are anchoring junctions (zona/zonula adherens)?
Adherent junctions: link submembrane actin bundles of adjacent cells.
What are transmembrane cadherin molecules?
They bind to each other in the extracellular space, and, through link molecules, to actin of the cytoskeleton.
What is the function of desmosomes?
Link submembrane intermediate filaments of adjacent cells. Also called macula adherens. Desmosomes are very common in the skin where they provide mechanical stability.
What is the function of communicating junctions?
Allow selective diffusion of molecules between adjacent cells. Often termed gap junctions.
What is each circular patch of communicating junctions patched with?
Several hundred pores.
What are pores of gap junctions produced by?
Connexon proteins.
Where are gap junctions found?
In epithelia, but also in some smooth muscle and in cardiac muscle, where it is critical for the spread of excitation.
What is a junctional complex?
Close association of several types of junctions found in certain epithelial tissues.
