2.1 - Cell Structure. Flashcards
Revise all of Cell Structure.
What are prokaryotes?
Single-celled organisms (e.g Bacterial cell).
What are eukaryotes?
Complex multi-cellular organisms (e.g. Animal cell, plant cell).
What is the function of the plasma (cell surface) membrane?
Found on the surface of animal cells; inside the cell wall of plant cells.
Made of lipids and proteins.
Regulates the movement of substances in and out of the cell.
Has receptor molecules that allow it to respond to chemicals (like hormones).
What is the function of the cell wall?
Supports and strengthens the cell.
What is the difference between a bacterial cell wall and a plant cell wall?
A plant cell wall is made of cellulose.
A bacterial cell wall is made of peptidoglycan.
What is the function of the nucleus?
Contains genetic material.
Controls the activities of the cell.
Surrounded by the nuclear envelope (double membrane).
Contains chromatin.
What is the function of the nucleolus?
Assembles the ribosomes.
What is the function of the nuclear pores?
They allow substances to move between the nucleus and the cytoplasm.
What is the function of lysosomes?
Contains hydrolitic enzymes that break down old worn out cell parts, and also digest and destroy pathogens (invading cells).
Surrounded by a membrane.
What is the function of ribosomes?
Site of protein synthesis.
Found on the RER.
Found in mitochondria.
Found in chloroplasts.
There are also free ribosomes in the cytoplasm.
Made up of RNA and proteins.
(No membrane).
Which molecules move across the plasma membrane?
Water, CO2, O2, Ammonia.
What is the function of the RER?
- Covered with ribosomes.
- Folds and processes proteins.
What is the function of the SER?
-Has no ribosomes.
- Synthesis and processes lipids
(E.g. oestrogen, testosterone).
What is the function of the vesicles?
- Small fluid filled sac in the cytoplasm.
Surrounded by membrane.
-Transports substances in and out of the cell (via plasma membrane).
(Formed by the golgi apparatus, ER).
What is the function of the golgi apparatus?
- Fluid-filled, membrane bound, flattened sacs.
It further modifies, processes and packages lipids and proteins.
It also makes lysosomes.
What is the function of the mitochondria?
Have double membrane.
Site of aerobic respiration, produces ATP.
What is the function of the chloroplasts?
Flattened structure in plant cells.
Site of photosynthesis.
Surrounded by a double membrane.
Has membranes inside called thylakoid membranes.
What are the structural differences between chloroplasts and mitochondria?
1) In chloroplasts the membranes are stacked as grana and thylakoid membranes.
In mitochondria the inner membrane is folded into cristae.
2) Cristae contains enzymes.
Thylakoids contain chlorophyll.
How many layers does a bacterial cell wall have?
3 layers.
Capsule, cell wall, cell membrane.
What is the function of the centrioles?
Small hollow cylinders, made of microtubules.
- They are involved in the separation of chromosomes during cell division.
What is the function of cilia?
Small hair like structures found in the trachea, bronchi and bronchioles.
Have an outer membrane.
(Had a 9 +2 formation of microtubules).
-Microtubules allow the cilia to move. This movement is used by the cell to move substances along the cell surface.
What is the function of the flagella?
Microtubules contract to make flagellum move.
Flagella are use like the outboard motors used to propel cells forward.
-Used for motility (movement).
What is the difference of the cilia in eukaryotic cells and prokaryotic cells?
- Eukaryotic flagella and cilia is made up of tubulin.
- Bactetial cilia is made up of flagellin.
What are the similarities between prokaryotes and eukaryotes?
- Both have membranes.
- Both have DNA.
- Both have ribosomes.
What are the differences between prokaryotic and eukaryotic cells?
- Prokayotes do not have a nucleus.
- Prokaryotes do not have membrane-bound organelles (e.g - mitochondria, lysosomes, chloroplasts, RER, ER).
- Ribosomes in Eukaryotes are larger.
Why do cells have organelles?
Organelles provide the distinct conditions for chemical reactions to take place that contribute to the survival of cells.
What are the characteristics of stem cells?
Unspecialised (has no specific function).
Undifferentiated (has no special shape or form).
What is a stem cell?
Unspecialised and undifferentiated cell that can be turned into a specialised cell to perform specific functions.
Explain ‘differentiation’.
Differentiation causes change in gene expression.
This causes the production of specific proteins.
This results in changes in cell shape, size and function.
Define ‘totipotent’.
-Can differentiate into any type of cell (can turn into a whole organism).
Define ‘pluripotent’.
Can form all types of cell but not whole organisms.
Which types of embryonic stem cells have the highest levels of potency?
Pluripotent and totipotent.
Define ‘multipotent’
Can only form a range of cells within a certain type of tissue.
Where are multipotent cells found?
In the bone marrow (and have lower levels of potency).
Give an example of a multipotent stem cell.
Haemotopoetic stem cell.
What does the Cytoskeleton consist of?
Microtubules.
Microfilaments.
Intermediate filaments.
What are microtubules?
Made up of a protein called tubulin.
Microtubules are used to make eukaryotic cilia and flagella.
Act as tracks for the movement of vesicles around the cell.
They generate spindle fibres (these are used for segregation of cells) during cell division.
What are microfilaments?
Made up of a protein called actin.
They enable muscles to contract and white blood cells
Involved in cell contraction during cytokenesis.
What are intermediate filaments?
Made of proteins, thinner than microtubules.
The anchor organelles into place.
Give mechanical strength to cells and help maintain their integrity.
How do cells make extracellular proteins?
1) DNA carries instructions (genetic info) on how to make a particular protein.
2) This DNA is then transcribed to form MRNA.
3) The MRNA contains a copy of the instructions (that was carried by the DNA).
4) This newly formed MRNA leaves the nucleus via a nuclear pore and binds to a ribosome on the RER.
5) The ribosome reads the MRNAs genetic code (instructions) and assembles proteins in the correct sequence to form a chain of amino acids linked by peptide bonds to form a polypeptide (protein)
6) This protein then breaks off the ribosomes and gets folded and modified as it passes through the RER.
7) It then leaves the RER through vesicles that move through the golgi where the protein is the further modified, processed and packaged.
8) This fully formed protein then leaves the golgi through secretory vesicles that move to the cell membrane and are released out of the cell through a process known as cytokenesis.
How to prepare a Microscope slide?
If you want to look at a specimen under a light microscope, then you will need a stick it onto a slide.
How to prepare a dry mount?
1) You’ll need a thin slice of the specimen you want to look at.
2) Use tweezers to pick up your specimen and place it onto the middle of a clean slide.
3) Place a cover slip (thin, transparent glass( on top.
How to prepare a wet mount?
1) Start by pipetting a small drop of water onto a the middle clean slide.
2) Use tweezers to pick up your specimen and place it onto the water droplet.
3) To put your cover slip on, stand it slip upright, next to the specimen. Then carefully tilt and lower it on (avoid air bubbles they obstruct your view).
4) Next you can add a stain. Put a drop of stain on one edge of the cover slip. Then put a bit of paper towel onto the opposite edge of the cover slip.
This will cause the stain to get drawn under the slip , across the specimen.
Why is a stain used in microscopy?
To enhance visualisation, and to make the stain more visible.
Why is the cover slip in microscopy lowered gently?
To avoid any air bubbles as these bubbles can obstruct view.
Why is a microscope set at the lowest magnification first?
This is because the lowest magnification has the highest field of view, making it easier to locate the specimen.
Define ‘field of view’.
The point of focus. The area visible through the microscope.
Define ‘depth of view’.
The area in front and behind the specimen which is in focus.
At what power is the coarse adjustment knob used?
Low power.
Why is the coarse adjustment knob used?
To bring the specimen into focus on low power.
Why is the fine adjustment knob used?
To produce a sharpened image of the specimen.
(Exam question) What is the graduated measuring scale placed on the microscope stage?
The stage micrometer.
What are the two parts of a light microscope that magnify the specimen?
The eyepiece (the ocular). The objective lens.
What are the detailed structures of cells visible only with a electron microscope?
Ultrastructure (inner details of structure inside a cell).
Where is the eyepiece graticule fitted?
Into the eyepiece.
What is the stage micrometer used to work out?
Used to work out the value of divisions on the eyepiece graticule at a particular magnification.
What is the function of a vacuole?
A storage structure of a plant cell.
The perform functions such as: ingestion, digestion, excretion and expulsion of excess water.
They help maintain water balance.
What is the source of illumination, magnification, and resolution of a light microscope?
Light microscopes use light.
Magnification: x1500.
Resolution: 0.2 micrometers.
What are Laser Scanning Confocal Microscopes?
They use laser beams to scan a specimen.
This laser beams are tagged with a fluorescent dye.
The laser causes the dye to flouresce, giving off light. This light is then focused through a pinhole onto a detector. The detector is then hooked onto a computer, and the computer produces a 3d image.
Advantage - Can look at objects at different depths in thick specimens.
What does a pinhole do?
It blocks out-of-focus light.
This produces a much more clear image.
What are Transmission Electron Microscopes?
They use electromagnets to focus a beam of electrons, this is transmitted through a specimen.
Denser parts of the specimen absorb more electrons (creating contrast), which makes the denser parts look darker when an image is produced.
Can only be used to look at thin specimens.
Generates 2D Images.
What is the magnification and resolution on a TEM?
Magnification: x 1,000,000
Resolution: 0.0002 micrometers.
What are Scanning electron microscopes?
These scan a beam of electrons across a specimen.
This knocks off electrons off the specimen, these are gathered in a cathode ray tube to form an image.
Produces a 3D image.
Magnification: x 500,000
Resolution: 0.002 micrometers.
Differences between electron microscopes and light microscopes.
Electron microscopes have a magnification, resolution, more expensive.
Light microscopes are easier to use, cheaper, unaffected by electromagnetic fields.
However, light microscopes have lower frequencies and longer wavelengths.
What are ‘artifacts’?
False structures found in transmission electron microscopes.
State the different types of stains.
Simple stain - Uses a single stain.
Differential stain - Multiple stains.
Gram Staining - Used to differentiate gram positive (purple stain) and gram negative bacteria (red stain).
How do you stain light microscopes?
Use a dye (e.g. methylene blue, eosin).
The stain is take up by some parts of the object more than others, this creates contrast, this produces an image.
Different stains make up different things.
More than one stain can be used.
How do you stain electron microscopes?
Objects are dipped in a solution of heavy metals (lead).
The metal ions scatter the electrons, again creating contrast - some parts of the object show up darker than others.
Preparation technique for Electron microscopes.
1) Fixing - preserving structures by making cross links in the tissue using chemicals like formaldehyde/ gluteraldehyde.
2) Dehydration - Drying out tissues using solvents (e.g. acetone).
3) Embedding - Injecting a resin into the specimen to make it hard.
4) Sectioning - Slicing the specimen very thinly using a ultramicrotome.
5) Staining- Dipping specimens into a solution of heavy metals (e.g - lead).
