Lecture 1: Cell Structure Flashcards
What is a cell?
It is the basic unit from which living organisms are made, consisting of an aqueous solution of organic molecules enclosed by a membrane
Define tissue
it is an organized assembly of specialized cells subserving a generalized function
What is histology?
the study of tissues?
What is a system?
it consists of several organs whose functions are interrelated
What is an example of a system?
the urinary system which is composed of the kidneys, ureters, bladder, etc.
What are the basic components of a cell?
the plasma membrane, the nucleus, the cytoplasm, and the cytoskeleton
Define Plasma Membrane
a biomolecular leaflet of phospholipids between two protein coats
Define Nucleus
it is the most prominent organelle in a eukaryotic cell and is enclosed by two concentric membranes that form the nuclear envelope
What is the nuclear envelope made up of?
two layers of phospholipid
Define cytoplasm
it is the transparent substance around the nucleus that fills the rest of the cell’s interior
What makes up the cytoplasm?
it consists of cytosol and a large number of membrane bound organelles
Why does the cytosol behave more like a water-based gel than a liquid?
it contains a host of large and small molecules that crowd together closely
Define cytoskeleton
It is a system of protein filaments in the cytoplasm of the eukaryotic cell that gives a cell a polarized shape and the capacity for direct movement
What are the cytoskeleton’s most abundant components?
actin filaments, microtubles, and intermediate fiaments
Why are the protein filaments important?
they are responsible for maintain/changing the plasma membrane of the cell
What is the lipid bilayer of a protein comprised of?
phospholipid molecules with hydrophobic tails pointing inward and hydrophilic heads pointing outward
What are some examples of membrane proteins?
transporters, linkers, receptors, and enzymes
What is significant about membrane proteins?
carries out most membrane functions
What reinforces the plasma membrane?
the cell cortex
What is the cell cortex?
a specialized layer of cytoplasm consisting of a meshwork of fibrous proteins that is attached to the inner face of the plasma membrane
Define glycocalyx
a sugar coating of oligosaccharides and polysaccharides found on the exterior of the cell membrane
What is significant about a glycocalyx?
- it appears as a “fuzzy coat” at the ultrastructural level
- serves to protect and lubricate the cell, may contain enzymes(intestine)
- Is important in cell-cell recognition and adhesion
Define a ribosome
They are 10-20nm cytoplasmic particles composed of ribosomal RNAs and ribosomal proteins that associate with messenger RNA and catalyze the synthesis of proteins
Where are ribosomes found?
in clusters as polyribsomes or associated with membranes of the ER
Why are ribosomes important?
ribosome biogenesis and translation are regulated at multiple levels and are associated with accurate cell growth and proliferation.
What are signal sequences?
a relatively short amino acid sequence that directs a protein to a specific location within a cell (to a particular organelle)
How many amino acids does a signal sequence contain?
15-60
What are two other names for a signaling sequence?
a signal peptide or a targeting sequence
What is significant about the amino acid sequence in a signaling sequence?
it isn’t so much important what the sequence of the amino acids are but where the charged amino acids appear in the sequence
Define the Endoplasmic Reticulum
it is a membrane-bounded compartment in the cytoplasm of eukaryotic cells where lipids are secreted and membrane-bound proteins are made
Define RER
rough ER; region of the ER associated with ribosomes that is involved in the synthesis of secreted and membrane-bound proteins
Define SER
smooth ER; region of the ER not associated with ribosomes
What are the three main functions of the SER?
- involved in the synthesis of lipids(steroids)
- metabolism of lipid soluble substances
- regulates the concentration of calcium in muscle cells
What are the differences between the appearance of SER and RER when staining?
SER does not stain
Define Golgi apparatus
it is a membrane bound organelle in eukaryotic cells where the proteins and lipids made in the ER are modified and sorted
Where are the Golgi usually located?
in the cell nucleus but sometimes distributed throughout the cytoplasm
What does the Golgi apparatus consist of?
- cisternae
- a cis face (or entry)
- an exit face (or trans)
What are cisternae?
a collection of flattened, membrane-bound sacs, piled up like stacks of place in the Golgi Apparatus
What are transport vesicles?
the mode of transport from the ER to golgi and the golgi to the other compartments of the endomembrane system
What do golgi apparatuses look like with H&E and triple stains?
clear and referred to as the golgi vacuole
Define lysosome
membranous sacs of hydrolytic enzymes that carry out the controlled intracellular digestion of both extracellular materials and worn-out organelles
Three pathways involving lysosomes
- phagocytosis
- autophagocytosis
- hydrolytic enzymes
Define phagocytosis
internalization of large particles like bacteria or of small macromolecules and the vesicles fuse with the lysosome
Autophagocytosis
degradation of internal organelles
Hydrolytic enzymes
secreted to digest extracellular components
Why are lysosomal membrane proteins highly glycosylated?
the sugars, with cover much of the protein surfaces facing the lumen protect the proteins from digestion by the lysosomal proteases
What are secondary lysosomes?
they are endosomes fused with primary lysosomes
Define Autolysis
the digestion of cell contents when lysosomal membranes rupture(in the absence of oxygen) releasing the hydrolytic enzymes
Define mitochondria
the chief energy source of the cell that are similar in size and shape to bacteria; they contain their own DNA and RNA and a complete transcription and translation system including ribosomes
What is shape of mitochondria?
varies from rods to spheres
How many membranes does mitochondria have?
two, an outer and an inner
What is the inner membrane of mitochondria responsible for?
has tubular folds termed cristae that serve to increase its surface area for metabolic activity and is also the site of enzymes associated in electron transport and phosphorylation
What is the outer membrane of mitochondria responsible for?
contains proteins involved in mitochondrial lipid synthesis and is permeable to all molecules of 5000 daltons or less
The matrix of the mitochondria
large internal space containing highly concentrated mixture of hundreds of enzymes including those required for the oxidation of fatty acids an pyruvate during the citric acid cycle
What is the function of the mitochondrial matrix granules?
to bind cations (especially CALCIUM)
What are the main functions of mitochondria?
- ATP production and electron transport
- role in calcium sequestration
- participation in the apoptosis cascade that results in the neurodegeneration and cell death
Define Proteasome
a large multifunctional protease complex in the cytosol that degrades intracellular proteins marked for destruction by attachment of multiple ubiquitin molecules.
What is the function of a proteasome?
degrades a variety of endogenous protons including transcription factors, cyclins, proteins encoded by viruses and other intracellular parasites, and proteins that are folded incorrectly
What is it important that proteasomes degrade cyclins?
they must be destroyed so that the next step of the cell cycle can occur
Why is the ubiquitin-proteasome system significant?
essential for cell viability and abnormalities of the system can lead to degenerative diseases and some types of cancer.
Structure of a proteasome
cossets of a core particle in the form of 4 rings and 2 regulatory particles that have binding sites to recognize the protein ubiquitin
What happens to proteins that are destined for destruction?
they are bound to the ubiquitin molecule and unfolded by ATPases associated with the regulatory particle –> the unfold protein is translocated into the central cavity of the core particle –> several active sites in the core particle break various specific peptide bonds of the protein
