2.1.1 - Cell Structure Flashcards
What does a microscope allow us to do
Magnify an object many times
Eyepiece graticule
Circular disk that fits onto the eyepiece and contains a tiny ruler with equal divisions on it
Stage micrometer
Usually 1-100nm long with 100 divisions on it. This sits on the stage of the microscope and is used to calibrate the eyepiece graticule
Why do we need a stage micrometer to calibrate the eyepiece graticule
The eyepiece graticule remains constant no matter what magnification the cells are used at
What are the two types of objective lens in a compound light microscope
High power
Low power
What instrument was used before the first microscope
Magnifying glasses
What type of microscope did Robert Hooke invent
A compound light microscope
What is the main feature of compound microscopes
They have 2 types of lenses, the eyepiece and objective lenses
In what year was the electron microscope invented in
1931
What is an advantage of an electron microscope
Capable for far greater resolution and magnification of 1 mil.
What is a disadvantage of electron microscope
Living specimens are destroyed by high dose of radiation
Metric equivalent of decimetre, dm
1 x 10^-1 m
Metric equivalent of millimetre, mm
1 x 10^-3 m
Metric equivalent of micro metre
1 x 10^-6 m
Metric equivalent of nanometre, nm
1 x 10^-9 m
What does the amount of detail seen through a microscope depend on
The resolving power of the microscope
Resolving power
The smallest separation at which two separate objects can be distinguished (or resolved)
What is the resolving power of a microscope ultimately limited by
The wavelength of light
What is the wavelength of light
400-600nm
Why do some microscopes have blue filters
Blue has the shortest wavelength of visible light and to improve the resolving power a shorter wavelength of light is needed
Definition of magnification
How much bigger a sample appears to be under the microscope than it’s in real life
Definition of resolution
Ability to distinguish between two points on an image i.e. the amount of detail
What is the resolution of an image limited by and why
The wavelength of radiation used to view the sample
When objects in the specimen are smaller than half the wavelength of the radiation being used, they don’t interrupt the waves, and so aren’t detected
What is the wavelength of light much larger than
The wavelength of electrons, so the resolution of the light microscope is a lot lower
How does using a microscope with a more powerful magnification affect the resolution
It does not
It will increase the size of the image but objects closer than 200nm will still only be seen as one point
Compound microscopes
Use several lenses to obtain high magnification
Resolution of light microscopy
About 200nm, which is good enough to see cells, but not details of cell organelles
Examples of procedures undertaken to prepare slide samples
Fixation Dehydration Embedding Sectioning Staining Mounting
Light microscopy
Specimens are illuminated with light, which is focussed using glass lenses and viewed with the eye or photographic film.
Specimens can be living or dead, but often need to be stained with a coloured dye to make them visible
What is the wavelength of electrons
Less than 1nm, so can be used to resolve small sub-cellular ultra-structure
How did the electron microscope revolutionise biology
Allows organelles such as mitochondria, ER and membranes to be seen in detail for the first time
Problems with an electron microscope
Specimens must be fixed in plastic and viewed in a vacuum, and must therefore be dead
Specimens can be damaged by the electron beam
Specimens must be stained with an electron-dense chemical (usually heavy metals like osmium, lead or gold)
What are the two types of electron microscope
Transmission Electron Microscope (TEM)
Scanning Electron Microscope (SEM)
TEM
Works much like a light microscope, transmitting a beam of electrons through a thin specimen and then focusing the electrons to form an image on a screen or on film
Most common form of electron microscope and has best resolution
SEM
Scans a fine beam of electron onto a specimen and collects the electrons scattered by the surface
Has poorer resolution but gives excellent 3D images
Laser scanning confocal microscope
Used to observe an object at a certain depth within a cell
Why do we stain samples
To ensure contrast between structures
Identification of cells
Magnification of light microscope
X1500
Magnification of TEM
X500,000
Resolution of TEM
0.2 nm
Magnification of SEM
X100,000
Resolution of SEM
10nm
Method of laser scanning confocal microscopy
Using a laser light to scan an object point by point and a computer assembles the image
Pros of laser scanning confocal microscopy
Can be used to study whole, live specimens and can be used to obtain images at different depths in thick sections
Main stains
Haemoxylin
Eosin
Haemoxylin
Blue colour
Stains DNA and RNA in all nuclei
Often used together (differential staining)
Eosin
Pink or red colour
Stains connective tissue and substances in cytoplasm
IAM Equation
I
A M
I - image size
A - actual size
M - magnification
Eukaryotic Cells
Have a nucleus containing genetic info
Prokaryotic cells
Don’t have a nucleus
No membrane bound organelles
Organelles
Components of a cell, each with a different function
Membrane bound
Surrounded by a membrane
Structure of a nucleus
Double nuclear envelope Nuclear pores Nucleoli Membrane of nuclear envelope continuous with rough ER membranes Nucleoplasm containing chromatins
Function of nucleus
Contains genetic material (chromosomes)
Controls cell activities
Function of double nuclear envelope
To enclose and protect DNA
Function of nuclear pores
Allow entry of substances such as nucleotides for DNA replication and exit of molecules such as mRNA during protein synthesis
Function of nucleoplasm containing chromatin
It is these, during cell division, condense to form chromosomes
Function of the nucleoli
Assembles ribosomes, coenzymes, proteins and RNA
Function of outer membrane of nuclear envelope being continuous with rough ER
Makes perinuclear space continuous with the lumen of the ER, thus allowing easy transport of substances
Structure of mitochondrion
Double membrane
Inner membrane spanned by porins
Inner membrane folded to form cristae
Function of double membrane in mitochondrion
Isolates reactions of the Kreb’s cycle. Compartmentalisation allows high conc. of enzymes and substrates to be maintained
Function of innner membrane being folded in cristae
Increases the surface area for the attachment of enzymes
Roles of cytoskeleton
Allow organelle movement
Give support and mechanical strength
Keep the cell’s shape stable
Organelles in animal cells
Vesicles Lysosomes Nucleolus Golgi apparatus Mitochondrion Rough ER Smooth ER Centriole Cell membrane Cytoplasm Ribosome
Organelles in plant cells
Cell wall Cell membrane Golgi apparatus Chloroplast Amyloplast Vacuole Cytoplasm Mitochondrion Ribosomes Rough ER Smooth ER Lamella
DNA in eukaryotes
Linear
DNA in prokaryotes
Circular
DNA association in eukaryotes
Associated with proteins called histones
DNA organisation in prokaryotes
Proteins fold and condense DNA
Types of organelles in eukaryotes
Both membrane and non-membrane bound
Types of organelles in prokaryotes
Only non-membrane bound
Non-membrane bound organelles
Ribosomes
Centrioles
Cytoskeleton
Cell wall
Cell walls in eukaryotes
Chitin in fungi
Cellulose in plants
Not present in animals
Cell wall in prokaryotes
Peptidoglycan (bacteria)
Ribosomes in eukaryotes
Larger (80 S)
Ribosomes in prokaryotes
Smaller (70 S)
Reproduction in eukaryotes
Asexual or sexual
Reproduction in prokaryotes
Binary fission
Cell types in eukaryotes
Unicellular and multicellular
Cell type in prokaryotes
Unicellular
Organelles involved in protein synthesis
Nucleus Ribosomes Rough ER Vesicles Golgi apparatus
Organelles indirectly involved with protein synthesis
Nucleus (chromatin, nucleolus (RNA))
Smooth ER
First stage in protein synthesis
Proteins are synthesised on ribosomes bound to the RER (translation)
Second stage in protein synthesis
Proteins pass into RER cisternae and packaged into transport vesicles
Third stage in protein synthesis
Vesicles move towards Golgi apparatus via transport function of cytoskeleton, they fuse with the cis-face
Fourth stage in protein synthesis
Proteins are structurally modified as they pass through the Golgi cisternae and they leave the Golgi through the trans face
Fifth stage in protein synthesis
If the protein is to leave the cell (secreted), vesicles travel to cell surface membranes fuse with the membrane and the proteins are released
Lysosomes
Specialised forms of vesicles that contain hydrolytic enzymes
Responsible for breaking down water materials in cells
Play important role in apoptosis
Apoptosis
Programmed cell death
Vesicles
Membranous sacs used for storage and transport inside the cells
Single membrane with fluid inside
Cytoskeleton
Network of fibres necessary for shape and stability
The components of the cytoskeleton
Microfilaments
Microtubules
Intermediate fibres
Microfilaments
Contractile fibres from actin
Responsible for cell movement and contraction in cytokinesis
Actin
A protein
Cytokinesis
Process in which cytoplasm of a single eukaryotic cell forms 2 daughter cells
Microtubules
Scaffold-like structure determines shape of cell
Tracks for movement for organelles (vesicles) around cell
Form spindle fibres
What are microtubules made from
Polymerisation of globular tubulin
Spindle fibres
Have a role in physical segregation of chromosomes
Intermediate fibres
Give cells mechanical strength and help maintain integrity
Roles of cytoskeleton
Holds organelles in place
Controls movement of organelles
Gives support and mechanical strength
Keep cell’s shape stable
Centrioles
Component of the cytoskeleton composed of microtubules
Centrosome
Formed from two associated centrioles
Involved in the assembly and organisation of spindle fibres in cell division
Functions of flagella
Enable cells mobility
Used as sensory organelle detecting chemical changes in the cell’s environment
Types of cilia
Mobile
Stationary
Stationary cilia
Present on surface of cells
Important functions in sensory organs
Mobile cilia
Beat in a rhythmic manner (creating current) –> cause movement of fluids/objects adjacent to cell
Where is mobile cilia found
In the trachea
In the fallopian tubes
Cisternae
Fluid filled cavities that form transport channels
What is the smooth ER responsible for
Lipid and carbohydrate synthesis, transport and storage
What is the rough ER responsible for
Synthesis and transport of proteins
It’s an intracellular transport system
Structure of Golgi apparatus
Stack of cisternae
Secretory vesicles bring materials to and fro
Function of Golgi apparatus
Modifying proteins to make glycoproteins, lipoproteins or fold them into a 3D shape
Structure of chloroplasts
Double membrane
Thylakoids containing chlorophyll
Stroma
Granum
Each stack of thylakoids
Why do chloroplasts have a double membrane
Protection
Stroma
Fluid filled matrix in chloroplast
Vacuole
Filled with water and solutes
Maintains cell’s stability
How do vacuoles maintain cells’ stability
When the vacuole is full it pushes against the cell wall, making the cell turgid
Where are ribosomes made
In the nucleolus, as 2 separate subunits, which pass through the nuclear envelope into the cell cytoplasm and then combine
Some attach to the RER
What is the plant cell wall made from
Bundles of cell fibres
Function of plant cell walls
Provide strength and support
Maintains cell’s shape
Contribute to the strength and support of whole plant
Allow solutions (solute and solution) to pass through
Preparing a microscope slide - dry mount
Used for hairs, flowers, pollen etc
Sharp blade - individual cells are visible
Cut a thin slice - so light can pass through
Use tweezers to place your specimen onto your clean microscopic slide
Place a cover slip on top - making sure to not get fingerprints on it
Preparing a microscope slide - wet mount (prevents dehydration)
Use for liquid specimens e.g. blood smears and plant cells
Pipette water onto your slide
Add specimen to middle of slide using tweezers
Carefully tilt cover slip next to water droplet - ensure no air bubbles, obstructs view of specimen
Once slip is in position, add stain next to edge - will get drawn under slip across specimen
Role of membranes within cells
Compartamentalisation
Attachment site for enzymes
How does the cytoskeleton move organelles around
Shortening or lengthening microtubule
Motor proteins
Negative staining
Dyes such as Congo red are negatively charged and repel other negatively charged substances e.g. cytosol so will stay out of the cell
What is the cytoplasm made of
Cytosol - water, salts and organic molecules
