Section 2 - Cell Structure Flashcards
Define - Magnification
How much an image is enlarged under a microscope.
What is magnification controlled by?
The power of the lens used.
Define - Resolution
The minimum distance apart that two objects can be in order for them to appear as separate items
What is resolution controlled by?
The wavelength of the illumination used
Give ordered list of microscopes and their resolution power?
Light - low
SEM - high
TEM - Highest
What does SEM stand for?
Scanning electron microscope
What does TEM stand for?
Transmission electron microscope
What are the advantages of using a TEM?
Transmission electron microscope
- highest magnification and resolution ( as shorter wavelength of electrons)
- focuses using a condenser electromagnet
- produces 2D photomicrograph (digital)
What are the disadvantages of using a TEM?
Transmission electron microscope
- dead cells
- must be in a vaccum
- must cut specimen (thin specimen)
- complicated preparation may create artefact
- does not produce colour image
Define - Artefact
Error caused with something that is not part of natural specimen
How do TEM’s work?
Transmit electrons through a specimen
How do SEM’s work?
They scan for electrons by detecting electrons that bounce off a specimen.
What are the positives of using SEM’s?
Scanning electron microscope
- high resolution
- specimen doesn’t need to be thin
- focuses using a condenser electromagnet
- produces a 3D image using computer analysis
What are the negatives of using a SEM?
- dead cells
- must be in a vacuum
- complicated preparation may create artefact
- does not produce colour images
How can you calculate magnification?
Magnification = Image size / actual size
How does an eyepiece graticule do?
It helps us measure the size of an object
It is a way to measure with a scale of 10mm and divided into 100 sub-divisions
Why must you calibrate an eyepiece graticule?
All objective lenses have different degrees of magnification
How do you calibrate an eyepiece graticule?
- use a microscope slide called a stage micrometre
- this provides a second scale
- line up the eyepiece graticule scale and the stage micrometre to calculate the length of the divisions on the eyepiece graticule
- To calculate divide the differences in magnification.
- You must give in graticule units (gu) eg. X10 Magnification 1mm = 10gu 1/10mm = 1gu 0.1mm = 1gu
What is cell fractionation?
the process of breaking up cells and different organelles they contain in order to separate the organelles (by size) ready for study
What is the process of cell fractionation?
stage 1 - cold, buffered and isotonic solution
stage 2 - homogenisation
stage 3 - sieve to remove insoluble material
stage 4 - ultracentrifugation
what is stage 1 of cell fractionation?
Place fractionation cells in a cold, buffered and isotonic solution.
what is stage 2 of cell fractionation?
Homogenisation - cells are broken up by a homogeniser to release the organelles
Why are fractionation cells placed in a cold solution?
to reduce enzyme activity that could damage the organelles
Why are fractionation cells placed in a buffered solution?
to maintain a constant pH and prevent protein damage
Why are fractionation cells placed in a isotonic solution?
to prevent cell organelles bursting or shrinking(osmosis out)
Define - homogenisation
cells are broken up by a homogeniser to release the organelles
What is a homogeniser?
Basically a blender that breaks up cells for fractionation
what is stage 3 of cell fractionation?
the blended tissue is filtered though a sieve to remove insoluble materials eg. cell wall, large pieces of unhomogenised tissue and connective tissue
what is stage 4 of cell fractionation?
Ultracentrifugation -
- The filtrate is placed in centrifuge and spun at a slow speed.
- The heaviest organelles eg. the nucleus are forces to the bottom and form a thin pellet.
- The fluid at the top (supernatant ) is removed. The supernatant can be re spun at a faster rate to gain the next heaviest organelles.
- You should repeat this until all organelles are separated.
How is the supernatant?
The fluid that stays at the top during ultracentrifugation
Which individual helped discover the cell?
Robert Hooke - 1665
Why was the electron microscope such an important discovery?
It allowed scientists to see the complete ultrastructure of the cell.
What does the nucleus consist of?
- nuclear envelope
- nuclear pores
- nucleoplasm
- chromosomes
- nucleolus
What is the nuclear envelope?
- surrounds the nucleus
- lipid bilayer membranes
- Outer membrane is continuous with the ER and often has ribosomes on its surface
- controlling the entry and exit of materials in and out of the nucleus and the reactions taking place within it
What are nuclear pores?
- Allow the transport of molecules across the nuclear envelope
- RNA moving from the nucleus and proteins moving to the nucleus
- It is like holes in the envelope.
- typically 3000 pores in each nucleus
- each 40-100 nm in diameter
What is the nucleoplasm?
A granular, jelly-like material. The substance in cell’s nucleus that makes up the bulk of the nucleus and includes chromosomes and nucleolus
What are chromosomes?
- Made of nucleic acids and proteins - carries genetic information in the form of genes - consisting of protein-bound, linear DNA
What is nucleolus?
- A small spherical region within the nucleoplasm - It is the largest structure in the nucleus - It manufactures ribosomal RNA and assembles the ribosomes. - There may be more than one in a nucleus
What is the function of cytoplasm?
This is where all the reactions occur and it also holds all the organelles.
What is the function of the cell membrane?
This is selective and choses what goes in and out of the cell
What is the function of the ribosomes?
To secrete proteins. It is also made into a large and small section
What is the function of the mitochondria?
The power house of the cell - so aerobic respiration can produce energy in the form of glucose
What is the function of the cell wall?
To keep the structure off the plant cells. It is made of cellulose.
What is the function of the vacuole ?
This contains the cell sap and gives some structure
What does Mitochondria consist of?
- double membrane - cristae - matrix
What is the function of the double membrane?
- outer membrane covers mitochondria like a skin - inner membrane folds into a layered structure - the inner membrane increases the surface area
What is the function of the cristae?
- This is the fold made by the inner membrane of the mitochondria. - It gives more space for the attachment of enzymes and other proteins involved in respiration
What is the function of the matrix?
- The fluid inside the mitochondria - It has its own ribosomes and DNA floating in it - containing granules which help with ion concentration - Contains protein, lipids, ribosomes and DNA that allows the mitochondria to control the production of some of their own proteins - Many enzymes involved in respiration are found in the matrix
What is the function of their chloroplast?
It is the sight of photosynthesis
What does the chloroplast contain?
- Chloroplast envelope - grana - stroma
What is the function of the chloroplast envelope?
It is a double plasma membrane that surrounds the chloroplast organelles. It is highly selective in what it allows to enter and leave the chloroplast.
What is the function of the Grana?
- stacks of discs known as thylakoids up to 100 discs - within the thylakoids is the photosynthetic pigment chlorophyll - resembles a stack of coins - site of light-dependant reactions photosynthesis - connected by intergranal thylakoids - some have tubual extensions that join up with thylakoids in adjacent grana (where the first stage of photosynthesis takes place)
What is the function of stroma?
- colourless fluid surrounding grana - contains enzymes required for photosynthesis - DNA and ribosomes are also present - a fluid filled matrix where the second stage of photosynthesis takes place (synthesis of sugars) - also includes starch grains
What are the two types of endoplasmic reticulum ?
rough and smooth
What are the functional differences between the types of endoplasmic reticulum ?
rough - has ribosomes attached - involved in protein synthesis smooth - to do with lipids - other molecules are synthesised
What is the resolving power of a light microscope?
0.2pm - means that any objects closer than that will appear as a single item.
What is a limit of resolution?
It is up to this point that increasing magnification will reveal more detail but beyond it increasing the magnification will not do this and the item while larger will be more blurred
Why do light microscopes have a poor revolution?
A result of a relatively long wavelength of light
What is the advantage of electron microscopes over light microscopes?
- the electron beam has a very short wavelength and the microscope can therefore resolve objects well - it has a high resolving power - as electrons are negatively charged the beam can be focused using electromagnets
What is the revolution power of electron microscopes?
0.1nm apart - 2000 times better than a light microscope
What must be created in the chamber of an electron microscope in order for it to work effectively?
A near-vacuum
What is a graticule?
A glass disc that is placed in the eyepiece of a microscope. There is a scale etched on the glass disc.
Why would you record the results of calibration?
- If a specific objective lens then you can leave this attached to the microscope saving you time to have to recalibrate each time you use to measure the size of the object being viewed under the microscope
What is an ultrastructure?
The internal structure that suits the cells specific function.
What do eukaryotic cells have?
A distinct nucleus and possess membrane-bounded organelles
What is the function of the nucleus?
- Act as the control centre of the cell through the production of mRNA and tRNA and hense protein synthesis - retain the genetic material of the cell in the form of DNA and chromosomes - manufacture ribosomal RNA and ribosomes
What does the nucleus contain?
the organism’s hereditary material and controls the cells activity. Its using spherical
What is the role of mitochondria?
sites of aerobic stages of respiration (Krebs cycle and the oxidative phosphorylation pathway) - therefore responsible for the production of energy-carrier molecule, ATP, from respiratory substances such as glucose. - The number of mitochondria will vary with the level of metabolic activity
How are chloroplasts adapted for their function?
- granal membrane provides a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the first stage of photosynthesis. These chemicals are attached to the membrane in a highly ordered fashion - the fluid of the stroma possesses all the enzymes needed to make sugars in the second stage of photosynthesis - chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for photosynthesis
What is the ER?
Endoplasmic Reticulum
It is continuous with the outer nuclear membrane,
network of tubules and flattened sacs called cisternae
What is the function of the rough ER?
- Provide a large surface area for the synthesis of proteins and glycoproteins 2. Provide a pathway for the transport of materials, especially proteins, throughout the cell
What is the function of the smooth ER?
- synthesise, store and transport lipids - synthesise, store and transport carbohydrates
Describe the structure of the golgi apparatus?
- Similar to the SER but is more compact - stacks of membranes that make up flattened sacs (cisternae) with small rounded hollow structures called vesticles - Proteins made in ER pass though in strict sequence - The golgi modifies these proteins often adding non-protein components eg. carbohydrates. - Also labelling them allowing them to be accurately sorted adn sent to correct destinations - once sorted the proteins and carbohydrates are transported in Golgi cisternae - These vesicles may move to the cell surface, where they fuse with the membrane and release their contents to the outside
What is the function of the Golgi Apparatus?
- Add carbohydrate to proteins to form glycoproteins - produce secretory enzymes, such as those secreted by the pancreas - secrete carbohydrates, such as those used in making cell walls in plants - transport, modify and store lipids - form lysosomes
In what cells are Golgi Apparatus’ especially well developed?
Well developed in secretory cells, such as the epithelial cells that line the intestines
How are lysosomes formed?
When the vesicles produced by the Golgi Apparatus contain enzymes such as proteases and lipases.
What are lysozymes?
Enzymes that hydrolyse the cell walls of certain bacteria.