Chapter 6 - A tour of the Cell Flashcards
How do light microscopes work
use visible light and glass lenses to magnify and project images
- The lenses refract the light in a way that the image is magnified
- Allows us to study living cells
- Been revitalized recently by the addition of fluorescent markers and super resolution microscopy
Parameters in Microscopy
- Magnification: the ratio of an objects image size to its actual size
- Resolution: the clarity of the image; the minimum distance two points can be separated by and still be distinguished as separate points
○ Have a resolution of about 0.2 um - Contrast: the difference in brightness between the light and dark areas of an image
○ Enhanced through staining
- Resolution: the clarity of the image; the minimum distance two points can be separated by and still be distinguished as separate points
Electron Microscope
focuses a beam of electrons through the specimen or onto its surface for higher resolution imaging
- In order to prepare the specimen, it often leads to cells being killedT
Types of EM
- Scanning Electron Microscopes: Scans the surface of the sample which excites electrons, which these secondary electrons are then detected by a device which translates the electrons into an image of the specimen’s surface which appears to be 3d
○ especially useful for the detailed study of the topography of a specimen - Transmission Electron Microscope: aims an electron beam through a thin section of the specimen, which has been stained with atoms of heavy molecules and have attached to cellular structures, creating an image of the internal structure of cells
○ A new type was developed called Cryo-electron Microscopy which allows specimens to be preserved at extremely low temperatures, which allows visualization of structures in their cellular environments
Cell Fractionalization
a technique for determining cell structure and function by taking cells apart and separating major organelles and other subcellular structures
- Requires a centrifuge which spins the disrupted cells, while differential centrifuge separates components based on their size
○ At faster speeds, the smaller the components form the supernatant, at slower speeds, the pellets consist of larger components
Parts of an Animal Cell
- Nucleus:
○ Nuclear envelope:
○ Nucleolus:
○ Chromatin:- Endoplasmic Reticulum:
- Cytoskeleton:
- Mitochondria:
- Lysosomes:
- Golgi Apparatus:
Parts in a Plant Cell
- Nucleus
○ Nuclear Envelope
○ Nucleolus
○ Chromatin- Rough ER and Smooth ER
- Golgi Apparatus
- Mitochondrion
- Plasma Membrane
- Cell Wall:
- Plasmodesmata:
- Chloroplasts:
- Cytoskeleton
Central Vacuole
Nucleus
contains the genetic material in the form of chromosomes in eukaryotic cells
- Directs protein synthesis and is enclosed by the nuclear envelop which is a lipid bilayer with perforated pores
Nuclear Lamina
lines the nuclear envelope besides at the pores and is a network array of protein filaments which maintain the shape by mechanically supporting the envelope
- Assisted by the nuclear matrix which extend throughout the nuclear interior
- Both help organize genetic material so it functions effectively
Nucleolus
a structure in the nucleus consisting of chromosomal regions containing and synthesizing rRNA molecules as well as assembling Ribosomes
- Can be two or more depending on species and stage of cells reproductive life cycle
Ribosomes
complexes made of rRNA and proteins which carry out protein synthesis
- Not considered organelles and lack a membrane
- can either be free floating in the cytosol and create proteins that function in the cytosol
- Can also be bound ribosomes which create proteins destined for membrane insertion, organelle packaging and secretion
Endomembrane system:
carries out protein synthesis, protein transport in and around the membrane and organelles, the metabolism and movement of lipids as well as detoxification of poisons
- Membranes are connected either physically or through vesicular transfer
Includes:
- nuclear envelope,
- endoplasmic reticulum,
- golgi apparatus,
- lysozomes,
- various type of vesicles and vacuoles
- plasma mebrane
Endoplasmic Reticulum
an extensive network of membranes that are called cisternae
- its a membrane which separates the internal compartment known as the lumen/cisternal space from the cytosol
- both smooth and rough ER
Function of Smooth ER
- Important in synthesizing lipids, including oils, steroids and new membrane phospholipids
- help detoxify drugs and poisons by usually adding hydroxyl groups to drug molecules making them more water soluble and able to be flushed out
- stores calcium ions in the ER lumen of muscle cells
Functions of RER
- Synthesizes and secretes proteins such as glycoproteins; proteins with carbohydrates covalently bonded to them
- Is a membrane factory for the cell and grows by adding membrane proteins and phospholipids to its own membrane
Golgi Apparatus
consists of stacks of flat membranous sacs that modify, store and route products of the ER(proteins)
- Extensive in cells specialized for secretion
- Has distinct cis and tran faces for the membranous stacks which are respectively the receiving and secreting sides
○ Cis means same side, referring to the same side as ER
Functions of the GOlgi
- Products which pass through the golgi are modified in the transit from cis to tran sides
- Golgi also manufactures molecules like polysaccharides
- Involved in sorting and exporting of molecules by tagging them to direct where they go in or out of the cell through vesicles
Cisternal Maturation Model
states the cisternae progress forward from cis to trans regions, carrying and modifying molecules as they move
- Reality may be that there is movement in the outer regions while the inner remains still
Lysosomes
membranous sac of hydrolytic enzymes which many eukaryotic cells use to hydrolyze macromolecules
- Excessive leakage from large number of lysosomes can destroy a cell by self-digestion, 1 breaking down will not
- Created by the rough ER and transferred to the Golgi for processing
Process of Lysosome Digestion
- Phagocytosis:
○ engulf smaller organisms which allows the food vacuole to be fused to a lysosome
○ Enzymes digest the food and products such as sugars, amino acids pass into the cytosol- Autophagy: cell renewal/recycling
○ a damaged organelle, becomes surrounded by a double membrane which a lysosome then fuses with
○ Lysosome enzymes dismantle the inner membrane and enclosed material resulting in small organic compounds being released into the cytosol for reuse
- Autophagy: cell renewal/recycling
Lysosome Storage Disease
when hydrolytic enzymes are lacking leading to the accumulation of indigestible material and interferences with cellular activities
Vacuoles
large vesicles derived from the endoplasmic reticulum and golgi apparatus which has specialized functions in different cells
- Have elective membranes which transport solutes
Types:
- food vacuoles
- contractile vacuoles
- hydrolytic vacuoles
- central vacuoles
Mitochondrion
the sites of cellular respiration which uses oxygen to drive the production of ATP by extracting energy from bonds between sugars, fats and other fuels
- Found in nearly all eukaryotic cells including plant and fungi cells
- The number of mitochondria’s in a cell directly correlates with the cell levels metabolic activity
Can move around, change shape and fuse and divide into fragments; it’s a dynamic organelle
Structure of Mitochondrion
- Each of the two membranes enclosing are phospholipid bilayers with unique collections of embedded proteins
inner foldings called cristae which due to their folding, give the inner membrane a large surface area, enhancing its productivity of cellular respiration
- Intermembrane space is the narrow region between the inner and outer membrane
- Mitochondrial matrix is enclosed by the inner membrane which contains many different enzymes as well as mitochondrial DNA and ribosomes
Chloroplasts
- Chloroplast: found in plants and algae, are the site of photosynthesis which converts solar energy to chemical energy by absorbing sunlight and using it to synthesis sugars from Co2 and water.
- Contain chlorophyl, and other enzymes and molecules associated with the photosynthetic production of sugar
- dynamic in behavior like mitochondria
Structure of Chloroplasts
- The contents are partitioned from the cytosol by an envelope consisting of two membranes, separated by a narrow intermembrane space
- Inside the membranous system are thylakoids in the form of flattened, interconnected sacs which can be stacked into granums and contain chlorophyl pigments
- The fluid outside the thylakoids is the stroma which contains Chloroplast DNA as well as ribosomes and enzymes
Peroxisomes
a single membrane which contain enzymes that remove hydrogen atoms from various substrates and transfer oxygen
- Creates hydrogen peroxide(H2O2) which in itself is toxic, but the organelle contains an enzyme which converts it to water
- detoxifies in the liver
- uses oxygen to break down fatty acids as fuel for cellular respiration
Cytoskeleton
a network of fibers extending throughout the cytoplasm and serve a variety of mechanical, transport and signaling functions
- Prokaryotes also have similar cytoskeletons made up of proteins
- Made up of 3 fibres; microtubes, microfilaments, intermediate filaments
Functions of Cell Cytoskeleton: Support
- The most obvious function of the cytoskeleton is to give mechanical support to the cell and to maintain its shape
- Especially important for animal cells which lack cell walls
- Provides anchorage for other organelles and cystolic enzymes.
- Extremely dynamic and can be quickly dismantled and set up in a new location, changing the shape of the shell
Functions of Cytoskeleton: Cell Motility
the interaction with Motor Proteins to induce changes in cell location and the movement of cell parts
- Outside the cell, cytoskeletal elements and motor proteins work to move whole cells
- Inside the cell, vesicles use motor proteins ‘feet to walk’ along a track provided by the cytoskeleton.
Components of the cytoskeleton
Microtubules:a hollow rod composed of tubulin proteins which make up part of the cytoskeleton in all eukaryotic cells
- grow in length by adding tubulin dimers and can be disassembled when needed
Microfilaments: a twisted double chain of actin proteins which make up the cytoskeleton and work with myosin to cause cell contractions
- Can occur as linear or form structural networks when it binds with certain proteins
- Structural role is to bear tension
Intermediate Filaments: found in the cell of animals and made of keratin proteins coiled together which are specialized for bearing tension and are more permanent
- Intermediate in size between Microtubules and microfilaments
Function of Microtubules
- Support and shape the cell and serve as tracks with motor proteins can move along
- Guide vesicles from the ER to the Golgi and from the Golgi to the Plasma membrane
- Involved in the separation of chromosomes during cell division
Function of Microfilaments
-help support the cells cortex; shape
-They are known for their role in cell motility:
- actin and myosin filaments interact to cause contractions of muscular cells
- In some white blood cells and protists, actin and myosin are also involved in movement of cells which crawl along surfaces through pseudopodia
- In plant cells, actin-protein interactions contribute to cytoplasmic streaming
Function of Intermediate Filaments
- Sturdy and play a role in reinforcing the cell shape
- fixesand achors the position of organelles and nucleus
Cilia
Cilia: a short appendage containing microtubules
- Usually occur in large numbers on cell surface
Types of Cilia
- Motile cilia are specialized for locomotion or moving fluid past the cell
- Formed from a core of 9 outer doublet microtubules and two inner single microtubules unsheathed in an extension of the plasma membrane(9+2 arrangement)
- Primary cilium are non-motile and are arranged in a 9+0 arrangement acting as a single receiving antenna
Dyneins
found in cilia and flagella it’s a large motor protein extending between microtubule doublets with ATP hydrolysis driving the changes in dynein shape leading to the bending of cilia and flagella
- Typically has ‘two feet’ with one attached while the other reattaches one step further
Cell Wall
a protective layer external to that of the plasma membrane which protects the cell, maintains its shape and prevents excessive uptake of water
process of developing a cell wall
- Originally a young plant cell secretes a primary cell wall; a relatively thin and flexible wall which is glued to adjacent primary cell walls by the middle lamella
- When the cell stops growing some strengthen its wall by secreting hardening substances while others create a secondary cell wall; often deposited in several laminated layers with a strong and durable matrix that affords cell protection and support
Extracellular Matrix
the meshwork surrounding animal cells consisting of glycoproteins, polysaccharides and proteoglycans
- Super important in regulating cell life by communicating through integrins
- Can influence the activity of genes in the nucleus through chemical and mechanical signals
- Can coordinate the behavior of all cell tissue through triggering signaling pathways and changing the set of proteins
Cell Junctions in Plants
- Plasmodesmata: an open channel through the cell wall which connect the cytoplasm of adjacent cells allowing the transfer of water, small solutes and larger molecules to pass through
- Appear to move through with the help of the cytoskeleton
Types of Junctions in Animal Cells
- Tight Junctions: prevents the leakage of material through the space between cells
- Desmosomes: functions as rivet, fastening cells together
- Gap Junctions: consisting of proteins surrounding a pore allowing the passage of materials between cells which are similar to plasmodesmata however they are not lined with a membrane
