Studying Cells Flashcards
Examples of Eukaryotic Cells
Plants, algae, animal, protozoan, and fungi
What are features of a Eukaryotic Cell?
They have a nucleus and membrane bound organelles
Animal cell organelles
Nucleus
Nucleus membrane
Nuclear pores
Nucleolus
Rough Endoplasmic Reticulum
Smooth Endoplasmic Reticulum
Mitochondria
Golgi Apparatus
Cytoplasm
Cell surface membrane
Ribosomes
Lysosomes
Centromeres
Nucleus structure
Nuclear membrane and nuclear pores
Inside the nucleus there are chromatins
Nucleolus
Nucleus function
Stores genetic information
Site of DNA replication.
Site of transcription
Nucleolus function
Site of production of ribosomes
Mitochondrion structure
Double membrane
Inner membrane highly folded to form cristae (increase surface area)
Matrix containing mitochondrial DNA,
70s ribosomes
What does the matrix in mitochondria contain?
Mitochondrial DNA
What does the cristae in mitochondria do?
Increase surface area
Rough Endoplasmic Reticulum structure
Highly folded membranes with 80s ribosomes embedded.
The membrane is folded into flattened sacks called cisternae.
Joined to the nucleus.
Mitochondrion function
Site of ATP production by aerobic respiration.
Rough Endoplasmic Reticulum function
Synthesises and transport of proteins throughout the cell.
Smooth Endoplasmic Reticulum structure
Highly folded membranes flattened into sacks called cisternae
What are the highly membranes folded into sacks called? (For SER and RER)
Cisternae
Smooth Endoplasmic Reticulum function
Packages triglycerides into vesicles and transports them to the Golgi apparatus
(Eukaryotic) Ribosome structure
80s
Made up of 2 subunits that are made of long strands of rRNA
Ribosome function
Site of protein synthesis from amino acids.
Golgi Apparatus structure
Flattened sacs made of membrane filled with fluid.
Golgi vesicles pinch off from the main membrane.
Golgi Apparatus function
Sorts, modifies, and packages proteins and triglycerides into vesicles.
Lysosome structure
Membrane-bound organelle that stores and releases lysosomes
Lysosome function
Release lysosomes which hydrolyse pathogens in phagocytosis
Cell Surface Membrane structure
Made up of phospholipids, specific transport proteins, and carbohydrates arranged into a fluid mosaic model
Cell Surface Membrane function
Controls the passage of molecules in and out of the cell
Centrioles structure
Microtubules
Centrioles function
Form a network of spindle fibres onto which chromosomes attach.
Pull chromosomes apart during mitosis.
Chloroplasts structure
Granum
Thylakoid membrane
Stroma
Starch grains
DNA and 70s ribosomes
Granum function in chloroplasts
Stack of thylakoid membranes
Thylakoid membrane function in chloroplasts
Contains chlorophyll for photosynthesis
Contains ATP synthase enzyme to produce ATP.
Stroma function in chloroplasts
Where the photosynthesis reactions occur
Starch grains function in chloroplasts
The energy storage molecule in plants.
DNA and ribosomes function in chloroplasts
Used for synthesis of enzymes needed for photosynthesis
Cellulose cell wall in plants structure
Many WEAK hydrogen bonds between cellulose fibrils
The wall is permeable to most molecules
Has plasmodesmata which are gaps in the cell walls that connect cell cytoplasm’s together
What do the many weak H bonds between fibrils in cellulose cell walls do?
Makes the cell wall strong
Limits the volume of water that can move into the cell which stops osmotic lysis
What are plant cell walls made from?
Cellulose
What is fungi cell wall made from?
Chitin
Differences between plant cells and animal cells
Plant cells have a cellulose cell wall WHEREAS animal cells do not have a cell wall
Plant cells have chloroplasts WHEREAS animal cells do not have chloroplasts
Plant cells have a vacuole WHEREAS animal cells do not
Plant cells have carbohydrates stored as starch WHEREAS animal cells have carbohydrates stored as glycogen
Plant cells have no centrioles WHEREAS animal cells do have centrioles
Differences between prokaryotic cells and eukaryotic cells
In prokaryotic cells DNA is circular and not associated with histones WHEREAS in eukaryotic cells DNA is linear and associated with histones
In prokaryotic cells, there are no membrane bound organelles WHEREAS in eukaryotic cells, there are membrane bound organelles
In prokaryotic cells DNA is free in the cytoplasm WHEREAS in eukaryotic cells, there is a nucleus
Prokaryotic cells contain 70s ribosomes WHEREAS eukaryotic cells contain 80s ribosomes
Prokaryotes have a murein cell wall WHEREAS eukaryotic plant cells only have a cellulose cell wall
Prokaryotic cells may have a capside WHEREAS eukaryotic cells do not
Viruses definition
Viruses are ACELLULAR; they are not alive.
They are very small and they require a living cell to replicate inside.
Virus structure
Contain DNA or RNA, which can be single or double stranded.
Surrounded by a capsid
Has attachment proteins which enable it to bind to host cells
Has enzymes that is uses to replicate its genetic information and insert it into the host cell DNA
Methods of studying cells introduction
Scientists have developed ways to magnify and isolate these structures and organelles within cells for further study.
Light Microscope method
Specimens are illuminated with light, which is focused using glass lenses and viewed using the eye or photographic film
By using more lenses, a light microscope can magnify by a larger amount, but the problem is at these higher magnifications the microscope loses resolution. So, magnification is limited.
Problem with higher magnifications in light microscopes
At higher magnifications the microscope loses resolution. So, magnification is limited.
What does a shorter wavelength result in?
Better resolution
Why do light microscopes have a poorer resolution?
They have a higher wavelength
Types of electron microscopes
Scanning Electron Microscope
Transmission Electron Microscope
What type of image does a Scanning Electron Microscope produce?
3D
What type of image does a Transmission Electron Microscope produce?
2D
Procedure of Electron Microscopes
A beam of electrons illuminate the specimen.
Electrons have very small wavelength, so can be used to observe objects as small as ribosomes (20nm), this means the TEM & SEM produce images with HIGHER RESOLUTION.
What is the wavelength in electron microscopes?
Very small
Transmission electron microscope method
The electrons pass THROUGH the specimen.
Allows you to view organelles/internal structures.
Electrons are fired through the specimen
Less dense areas absorb less electrons and appear lighter
Denser areas absorb more electrons and so appear darker.
Scanning electron microscope method
Specimens are not sliced, and the electrons bounce off the SURFACE of the specimen.
Images are always in black and white.
Do TEM specimens have to be sliced?
Yes
Do SEM specimens have to be sliced?
No
Do specimens in light microscopes have to be dead or alive?
Can be dead or alive
Do specimens in electron microscopes have to be dead or alive?
Dead - they must be in a vacuum
Staining process for light microscopes
Very easy - coloured dyes
Staining process for electron microscopes
Very hard - can create artefacts (structures which are not actually there)
Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical (light) microscope
- Add a drop of water to the microscope slide;
- Get a thin section of plant tissue and float on the drop of water;
- Stain with KI solution;
- Lower the cover slip using a mounted needle to avoid air bubbles;
Cell centrifugation method - method of observing organelles
1: Tissue is homogenised in blender to break open the cells releasing the organelles into solution.
The solution must be:
Ice cold to reduce the action of enzymes that would digest organelles.
Isotonic so organelles don’t burst or shrivel
Buffered to stop pH changes which could denature proteins.
2: Filter the mixture to remove any large pieces of tissue/cells producing a solution of suspended organelles (supernatant).
3: Centrifugation of the supernatant by:
Centrifuge at HIGH speed The densest organelles (nucleus) are forced to the bottom of the tube into a pellet which is removed.
·Centrifuge at a HIGHER speed for a longer time. The next densest organelles are forced to the bottom of the tube into a pellet. This pellet is removed and can be re-suspended if required.
4: This process can be repeated many times, at higher speeds with each step. This separates the organelles (then molecules) according to their relative densities.
Why is the tissue homogenised in a blender? - Cell centrifugation
To break open the cells
What must the solution be in cell centrifugation?
Isotonic
Buffered
Ice cold
Why must the solution be isotonic in cell centrifugation?
so organelles don’t burst or shrivel
Why must the solution be buffered in cell centrifugation?
to stop pH changes which could denature proteins.
Why must the solution be ice cold in cell centrifugation?
to reduce the action of enzymes that would digest organelles.
What solution is formed after the tissue is homogenised and filtered?
Supernatant
Why is the supernatant centrifuged?
To obtain a pellet of the next densest organelle
Why must the centriguation be done at different speeds?
To obtain pellets of different densities
