Cells - Cell Structures Flashcards
Define magnification
By how much an image is enlarged under a microscope. It is controlled by the power of the lens used
Define resolution
The minimum distance between 2 objects at which a microscope can distinguish them as separate entities
What are the 2 types of electron microscope?
Transmission Electron Microscope
Scanning Electron Microscope
What are the benefits of Transmission Electron Microscopes?
Higher magnification than scanning and light
High resolution due to shorter wavelength of electrons
Focuses using a condenser electromagnet
Produces a 2D photomicrograph
What are the limitations of a Transmission Electron Microscope?
Cannot look at living cells
Must be in a vacuum
Must be a thin specimen
Complicated preparation may create an artefact
Does not produce a colour image
What are the benefits of a Scanning Electron Microscope?
Higher magnification than light
Specimen doesn’t need to be thin
Focuses using a condenser electromagnet
Produces 3D images using computer analysis
What are the limitations of a Scanning Electron Microscope?
Cannot look at living cells
Must be in a vacuum
Complicated preparation may create an artefact
Does not produce a colour image
Lower resolution than a TEM
Explain the process of cell fractionation
Cells are placed in a cold, buffered, isotonic solution:
- cold to reduce enzyme activity that could damage organelles
- buffered to maintain constant pH and prevent protein damage
- isotonic to prevent cell organelles bursting/shrinking
Explain the process of Homogenisation
Cells are broken up by a homogeniser to release organelles
Blended tissue is filtered through a sieve to remove insoluble material eg cell walls, connective tissue
Explain the process of centrifution
Filtrate is placed in a centrifuge and spun at a low speed
Heaviest organelles (eg nuclei) are forced to the bottom and form a thin pellet which is removed
Fluid at the top (supernatant) is removed
Supernatant re-spun at a faster speed to gain next heaviest organelles (eg chloroplasts)
What is used to measure objects with a microscope?
Eyepiece graticule and a stage micrometer
What is the process for calibrating an eyepiece graticule?
Line up the eyepiece graticule and stage micrometer under the desired magnification and calculate length of divisions
What are the 3 features of a mitochondria?
Double membrane
Cristae
Matrix
What is the double membrane in a mitochondria?
Outer membrane covers like skin
Inner membrane folded into layered structures -> increases surface area for respiration
What is the cristae in mitochondria?
Fold made by the inner membrane -> more space for chemical reactions to take place
What is the matrix in mitochondria?
The fluid within the organelle
It has its own ribosomes and DNA floating within it
Contains granules to help maintain ion concentration
What are the 5 different features of the nucleus?
Nuclear Envelope
Nuclear Pores
Nucleoplasm
Chromosomes
Nucleolus
What is the nuclear envelope?
Surrounds the nucleus and contains genetic info
Consists of 2 lipid bilayer membranes
What are nuclear pores?
Gaps that allow the transport of molecules across the nuclear envelope
This includes the movement of RNA and proteins
What is the nucleoplasm?
The substance of a cell’s nucleus
Includes chromosomes and nucleolus
What is the nucleolus?
Largest structure within the nucleus
Makes ribosomes
What are the 3 main components of a chloroplast?
Chloroplast envelope
Grana
Stroma
What is the chloroplast envelope?
Double membrane
- > outer membrane covers like skin
- > inner folded into layered structure
What is the grana?
Stacks of discs (individually known as thylakoids)
Site of light dependent photosynthesis
Connected by intergranal thylakoids
What is the stroma?
Colourless fluid surrounded the grana
Contains enzymes required for photosynthesis
DNA and ribosomes also present
What are the differences between the rough and smooth endoplasmic reticulum?
Rough is covered in ribosomes and makes proteins
Smooth isn’t covered in anything and makes lipids
What is the golgi apparatus?
The organelle that ‘packages’ and secretes proteins
What is the function of lysosomes?
to destroy unwanted / unneeded molecules (eg ribosomes that stop working)
contains very strong enzymes
What organelles do prokaryotes have that eukaryotes don’t?
Pili
Flagella
Chromosomal / Plasmid DNA
Capsule
What are pili?
Hair-like proteins surrounding a prokaryotic cell that help it attach itself to surfaces
What is the function of the capsule on a prokaryotic cell?
To prevent desiccation and chemical attack
What are the main structural features of a virus?
Attachment proteins OR a lipid envelope
DNA/RNA
Capsid
Matrix
Nucleoproteins
Define attachment proteins
Proteins on the outside of a virus that allows the virus to force itself onto the membrane of the host cell
Define a lipid envelope (viruses)
The outer membrane of a virus molecule that matches with the membrane of the host cell, allowing it to attach itself to a host undetected
Why do viruses have a lipid envelope or attachment proteins - not both?
They both have the same function -> to allow the virus to attach itself to a host cell
Define the capsid
The protein coat that encapsulates the DNA/RNA
Define nucleoproteins
Accessory proteins eg enzymes
Define the matrix (viruses)
Protein layer on the inside of the envelope
Describe the process of virus replication
- Virus attaches to host cell and injects genetic material
- Genetic material used as code to synthesize proteins
- New viral proteins assembled into new viruses
- Viruses burst out of the host cell, destroying it
