3: Cell Structure Flashcards
What is a nanometer in meters?
nm = m^-9
What is a micrometer
um = m^-6
What are the two types of microscopes?
Electron and light
What is the equation for magnification?
magnification = size of image / size of real object
What is the definition of magnification?
How many times bigger the image is in comparison to the object
What is resolution? (resolving power)
Minimum distance apart that two objects can be in order for them to appear separate
What is cell fractionation?
Process where cells are broken up and the different organelles they contained are separated out
What solution is required for cell fractionantion?
Cold, buffered, same water potential
Why does the solution for cell fractionantion have to be cold?
Reduce enzyme activity that might break down organelles
Why does the solution for cell fractionantion have to be buffered?
So the pH doesn’t fluctuate, as any change would cause a change in the organelle structure
What are the two steps of cell fractionation?
Homogenation and Ultracentrifugation
What is homogenation?
Cells are broken up by using a homogeniser (blender). Produces homogenate fluid, which is then filtered to remove large debris
What is Ultracentrifugation?
Homogenate is spun at very high speeds in order to create a centrifugal force and separate the different parts of the cell
What are the steps of Ultracentrifugation?
Tube of filtrate spun at low speed
Heaviest organelles (nuclei) are forced to the bottom where they form a sediment or pellet
Fluid at the top (supernatant) removed
Supernatant separately spun at faster speed
Mitochondria forms pellet, can be removed
Can be repeated for each organelle
What is the resolution of an optical microscope?
0.2 micrometer
What is the resolution of an electron microscope?
0.1 nanometers
Name some parts of the light microscope
Eyepiece Objective & Eyepiece lens Stage Diaphragm Light Source Base Fine & Coarse adjustment Arm Body Tube
What is the diaphragm of the microscope?
Allows different amounts of light to pass through the specimen
What speed of the centrifuge is needed to separate the nuclei?
1000 rpm
What speed of the centrifuge is needed to separate the mitochondria?
3500 rpm
What speed of the centrifuge is needed to separate the lysosomes?
16500 rpm
What is the supernatant?
The fluid at the top of the tube after the centrifuge process
What is the problem with a light microscope?
Poor resolution caused by relatively long wavelength of light
What are the two main advantages of an electron microscope?
High resolution - very short wavelength beam can be focused using electromagnets
What is the resolving power of a modern electron microscopes?
0.1nm
2000x better than light
Why does an electron microscope require a vacuum?
Absorbed or deflected in air
What are the two types of electron microscopes?
TEM - Transmission electron microscopeSEM - Scanning electron microscope
How does TEM work?
Electron gun produces beam of electrons Focused by condenser electromagnet Beam passes through thin specimen Thicker parts absorb them and are dark Electrons form image
What is the resolving power of TEM?
0.1nm
What can be done with the image of a TEM?
Photographed to produce a photomicrograph
What are the limitations of TEM & SEM?
Vacuum so no live specimens can be observed
Complex staining must be required - image not in colour
Specimen must be extremely thin
Image might have artifacts
What is an artifact?
Things that are created during the specimen in preparation, can be difficult to point out
What type of image is produced by TEM?
2-D Image
Does SEM require an extremely thin specimen
No
How does a SEM work?
Directs a beam of electrons to the surface of a specimen
Beam is passed back and forth across a portion of the specimen in regular pattern
Electrons scattered by specimen, how they scatter depending on contours
Build a 3-D image by computer analysis of the pattern of scattered electrons and secondary electrons
What is the resolving power of SEM?
20 nm
Not as good as TEM but better than light
What is used in light microscopes to measure the size of objects?
Eyepiece graticule
What is an eyepiece graticule?
Glass disc with scale
What is the usual length of a eyepiece graticule?
10mm
How many subdivisions are typically on an eyepiece graticule?
100
Why can the graticule not be used directly?
Different objective lenses have different magnifications
What is needed to calibrate the eyepiece graticule?
Stage micrometer
What is the size of the stage micrometer?
2mm
Sub-divisions are 0.01mm or 10um
How do you calibrate the eyepiece graticule?
Note how many divisions of a stage micrometer equal a number of epg divisons
1 stage micrometer subdivision = 10um
Work out epgu in um
What is the ultra-structure?
Internal structure of a cell which suits its function
What is a eukaryotic cell?
They have a distinct nucleus and have membrane-bound organelles
What is the diameter of a nucleus?
10-20um diamater (average)
What are the functions of the nucleus?
Controls cell through production mRNA and tRNA
Retain genetic information of cell
Manufacture ribosomal RNA and ribosomes
What are the sub parts of the nucleus?
Nuclear envelope Nuclear pores Nucleoplasm Chromosomes Nucleolus
What forms of genetic material is found in a nucleus?
DNA and chromosomes
What is the nuclear envelope?
Double membrane that surrounds the nucleus.
Controls entry and exit of materials
Contains reactions taking place
Continuous with ER
What are nuclear pores?
Allows passage of large molecules (RNA)
Around 3000 pores each 40-100nm in diameter
What is the nucleoplasm?
Granular, jelly-like material that makes up the majority of the nucleus
What are chromosomes?
Consists of protein bound, linear DNA
Where is the nucleolus?
Small spherical region in the nucleoplasm ( can be more than one)
What is the function of the nucleolus?
Manufactures ribosomal RNA and assembles ribosomes
What is the endoplasmic reticulum?
3-D system sheet-like membrane
Encloses a network of tubules and cisternae (flattened sacs)
What are the two types of endoplasmic reticulum?
Rough Endoplasmic Reticulum (RER)
Smooth Endoplasmic Reticulum (SER)
What is the difference between RER and SER?
RER has ribosomes present on the outer surface of membranes.
SER has no ribosomes
What are the functions of the RER?
Provides a large surface area for the synthesis of proteins & glycoproteins
What are the functions of SER?
Synthesise, store and transport lipids & carbohydrates
What are ribosomes?
Small cytoplasmic granules found in RER and cytoplasm
The site of protein synthesis
What are the two types of ribosomes?
80S - in eukaryotic cells, around 25nm in diameter
70S - prokaryotic cells, mitochondria and chloroplasts and smaller
What are ribosomes made from?
Composed of ribosomal RNA and protein
What is the structure of the golgi apparatus/body?
Cisternae (flattened sacs) with vesicles (small rounded hollow structures)
What are the functions of the golgi apparatus/body?
Modifies proteins so it canadd carbohydrates or lipids to proteins Produce secretory enzymes Form lysosomes Labels proteins Transport modify and store lipids
What happens to the modified proteins in the golgi apparatus/body?
Transported to vesicles for exocytosis, and remove them from the cell
In which type of cells is the golgi apparatus/body very common?
Secretory cells(epithelial cells that line the intestines)
How are lysosomes formed?
When vesicles produced by the golgi body contain enzymes
What are the enzymes found in lysosomes?
Proteases, lipases, and lysozymes (50 enzymes total)
Up to 1um in diameter
What are the functions of lysosomes?
Hydrolyse material by ingested by phagocytic cells (white blood cells)
Release enzymes to outside the cell (exocytosis) to destroy material
Digest worn out organelles Completely break down cells after they have died (autolysis)
What is the structure of the mitochondria?
Rod-shaped and 1-10um in length
Double membrane
Cristae
Matrix
What does the double membrane do in the mitochondria?
Controls entry and exit of material
What does the cristae do in the mitochondria?
Folded inner membrane provides a large surface area for the attachment of enzymes and other respirational proteins
What does the matrix do in the mitochondria?
Fluid containing protein, own lipids, ribosomes and mDNA.
Allows mitochondria to control production of own proteins
Respirational enzymes found here
What is the function of a mitochondria?
Site of aerobic respiration
Responsible for production of ATP
What are the features of the cell wall?
Consists of polyssacharides Thin layer (middle lamella) which marks boundary between adjacent cell walls and cements cells together
What are the functions of the cell wall?
Provide mechanical strength to prevent cell bursting under pressure by osmotic entry of water
Gives mechanical strength to plant as a whole
Allow water to pass along it and contribute to the movement of water
What are the cell walls of fungi made from?
Chitin
What are the cell walls in algae made from?
Cellulose or glycoproteins or a mix
What are the features of chloroplasts?
Carries out photosynthesis Disc. shaped 2-10um long and 1um in diameter
What is the structure of the chloroplasts?
Chloroplast envelope
Thylakoids stacked to make grana
Stroma matrix
What is the chloroplast envelope?
Double plasma membrane that surrounds the organelle, decides what enters and leaves the cell
What is a thylakoid?
Disc shaped structure that contains chlorophyll which stack to form grana where 1st stage of photosynthesis occurs
What is the stroma?
Fluid filled matrix where 2nd stage of photosynthesis occurs
Contains a large number of starch grains
How are they adapted to photosynthesis?
Granal membranes provide a large surface area for attachment of chlorophyll
Fluid of stroma has enzymes needed to make sugars for the 2nd stage
Ribosomes and DNA so they can manufacture proteins for photosynthesis
What is a vacuole?
Fluid filled sac bound by a single membrane (tonoplast)
Where is a vacuole found?
One large central vacuole in a plant cell
What does a vacuole contain?
Mineral salts Sugars Amino acids Wastes Pigments
What are the functions of the vacuole?
Support herbaceous parts of woody plants, by making cells turgid
Sugars and amino acids act as a temporary food store
Pigments may colour petals to attract pollinating insects
How can you tell the function of the cell?
Number and size of organelles
What is murein?
Polymer of disaccharides
Provides mechanical strength in cell walls
Are vacuoles found in animal cells?
Yes, however they are much smaller
What is the ultra-structure?
Internal structure of a cell which suits its function
What is a eukaryotic cell?
They have a distinct nucleus and have membrane-bound organelles
What is the diameter of a nucleus?
10-20um diamater (average)
What forms of genetic material is found in a nucleus?
DNA and chromosomes
What are ribosomes?
Small cytoplasmic granules found in RER and cytoplasm
The site of protein synthesis
What are the two types of ribosomes?
80S - in eukaryotic cells, around 25nm in diameter
70S - prokaryotic cells, mitochondria and chloroplasts and smaller
How common are mitochondria?
Occur in vast numbers
Account for around 25% of the dry mass of a cell
What is the structure of the golgi apparatus/body?
Cisternae (flattened sacs) with vesicles (small rounded hollow structures)
What is the function of a mitochondria?
Site of aerobic respiration
Responsible for production of ATP
What do cell walls consist of?
Microfibrilis of the polyssacharides, embedded in a matrix
What are the features of the cell wall?
Consists of polyssacharides Thin layer (middle lamella) which marks boundary between adjacent cell walls and cements cells together
What are the functions of the vacuole?
Support herbaceous parts of woody plants, by making cells turgid
Sugars and amino acids act as a temporary food store
Pigments may colour petals to attract pollinating insects
How can you tell the function of the cell?
Number and size of organelles
What is the order of the composition of an organism?
Organism -> Organ System -> Organs -> Tissues -> Cells
What type of cells for a tissue?
1 type of cells
What type of tissues form an organ?
Multiple tissues
Same function
Why are cells specialized?
Provide the best conditions for all functions
How are cells specialized?
Only some genes are activated (expressed) in the cells defining the cell
What is epithelial tissue?
Sheets of cells that line cells which are either protective or secretory function
What is a stem cell?
Cell which can differentiate
What are the three levels of stem cells?
Totipotent
Pluripotent
Unipotent
What does totipotent mean?
Cells can differentiate into any type of cell
What does pluripotent mean?
Can differentiate into many types of cell but not all
What does unipotent mean?
Cell can only replicate themselves
What is a prokaryotic cell?
Small cells and no nucleus or membrane bound organelles
What is the size of a bacteria?
0.1-10um in length
What is the cell wall made up of in bacteria?
Murein
What ribosomes are found in the bacteria?
70S
What is found in a bacteria cell?
Pilus Cell Wall Capsule Cell membrane Plasmid Flagellum Ribosomes Nucleiod Cytoplasm
What is a cell capsule made of?
Mucilaginous layer
What is the role of the capsule?
Protects bacterium from other cells and helps groups of bacteria to stick together for further protection
What is the purpose of circular DNA?
Possesses genetic material info for replication of cells
What is the role of the plasmid?
Possesses genes that may aid the survival of bacteria in adverse conditions
What is the size of virus cells?
20-300nm
What are the contents of a virus?
Nucleic acids
Capsid
Attachment proteins
What nucleic acids are found in viruses?
RNA and DNA
What is the capsid?
Protein coat
What virus has a lipid envelope?
Human immunodeficiency virus
Where and what are attachment proteins?
In the capsid
Allows the virus to identify and attach to a host cell
