2.1 Flashcards
Define Magnification
How much bigger an image appears compared with the original object
Define resolution
The ability to distinguish between two objects clearly
What do laser scanning microscopes do?
- they use laser light to scan an object point by point and assemble the pixel image and display it on screen
- the images are high resolution and show high contrast
- have depth selectivity and can focus on structures at different depths with a specimen - therefore they can be used to clearly observe the whole living specimen
TEM
- specimen has to be chemically fixed by being dehydrated and stained
- the beam of electrons passes through the speciemen
- the electrons form a 2D black and white image - this is called an electron micrograph
- has to be placed inside a vacuum
- needs to be coated with a fine film of metal
SEM
- electrons cause secondary electrons to bounce off of the specimen’s surface and can be focussed on a screen
- gives a 3D image
- black and white
- has to be placed in a vacuum
- has to be coated with a fine film of metal
Both types of microscope:
- are large and expensive
- need a great deal of skill to use
How does staining a cell enable components to become visible
Stain = contrast
Images seen in higher detail
Distinguish/see whatever you are looking for
Why are the optical microscope’s resolution limited?
they use visible light to produce images, therefore the microscope can’t produce an image that is smaller than the wavelength of visible light (400-700nm)
Therefore objects smaller than 200nm will appear as one object
Steps for using a light microscope:
- The specimen on a slide is placed on the stage and clipped into place
- Use the lowest power objective lens
- Adjust the coarse focus knob while looking into the eyepiece until the image is clear and in focus
- Adjust the iris diaphragm for optimum light
- Now use the 10x objective lens, then use the fine focus knob to focus the image
- Repeat step 5 using the x40 objective lens
What is a photomicrograph?
A photograph of the image seen using an optical microscope
Why is the resolution of an electron microscope much greater than optical microscope?
They use a beam of fast travelling electrons with a wavelength of about 0.004nm
How do electron microscopes work?
The electrons are fired from a cathode and focused by magnets (rather than glass lenses) on a screen or photographic plate
Both types of electron microscope are:
- large and expensive
- need a lot of skill to use
- specimen ave to be dead
- have to be viewed in a vacuum
- metallic salt stains used may be hazardous to the user
What is an organelle?
Membrane bound compartment within the cell each providing distinct environments and therefore conditions for different cell reactions
Why are most organelles in eukaryotes membrane bound?
This keeps the organelle separate from the rest of the cell, so that it is a discrete compartment.
Rough endoplasmic reticulum (RER) structure
- System of membranes, containing fluid filled cavities and are continuous with the nuclear membrane
- coated with ribosomes
What does iodine stain?
Stains cellulose in plant walls yellow
Chlorophyll - orange to blue black
What does methylene blue stain?
All purpose stain
What does eosin stain/
Cytoplasm
What does acetic orcein in do?
Binds to DNA and stains chromosomes dark red
What does Sudan red stain
Lipids
How to prepare specimen:
- dehydrate
- embedding them in a wax to prevent distortion during slicing
- using a special instrument to make very thin slices called sections - these are stained and mounted in a special chemical to preserve them
Function of the Rough endoplasmic reticulum
- intracellular transport system, cisternae form channels for transporting substances from one area of a cell to another
- provides a large surface area for ribosomes which assemble amino acids into proteins.
- proteins pass through the membrane into the cisternae and are transported to the Golgi apparatus for modification and packaging
Smooth endoplasmic reticulum (SER) structure
- system of membranes containing fluid filled cavities (cisternae) that are continuous with the nuclear membrane
- no ribosomes on its surface
What are cisternae?
Fluid filled cavities
Function of the Smooth endoplasmic reticulum
Contains enzymes that catalyse reactions involved with lipid metabolism, such as:
- synthesis of cholesterol
- synthesis of lipids/phospholipids needed by the cell
- synthesis of steroid hormones
It is involved with absorption, synthesis and transport of lipids
What is a vesicle?
A small fluid filled sac in the cytoplasm surrounded by a membrane, transports substances in and out of the cell, via the cell surface membrane and between organelles
Golgi apparatus structure
Consists of a stack of membrane bound flatten sacs
Secretory vesicles bring materials to and from the Golgi apparatus
Function of the Golgi apparatus
Proteins are modified for example by:
- adding sugar molecules to make glycoproteins
- adding lipid molecules to make lipoproteins
- being folded into their 3D shape
The proteins are packaged into vesicles that are pinched off and then:
- stored in the cell or
- moved to the plasma membrane, either to be incorporated into the plasma membrane or exported outside the cell
Mitochondria structure
- spherical, rod shaped or branched (2-5 um long)
- surrounded by two membranes with a fluid filled space between them. The inner membrane is highly folded - cristae
- the inner part o the mitochondrion is a fluid filled matrix
Function of the mitochondria
- the site of ATP production during aerobic respiration
- self replicating, so more can be made if the cell’s energy needs increase
- are abundant in cells where much metabolic activity takes place eg in liver cells and synapses
Chloroplasts structure
Large organelles, 4-10um long
Surrounded by a double membrane or envelope. The inner membrane is continuous with stacks of flattened membrane sacs called thylakoids which contain chlorophyll. Each stack or pile of thylakoids is called a granum. The fluid filled matrix is called the stroma
Chloroplasts contain loops of DNA and starch grains
Function of the chloroplasts
- the site of photosynthesise
- the first stage of photosynthesis (where light energy is trapped by chlorophyll and used to make ATP) occurs in the grana. Water is also split by H+ ions
- the second stage (where hydrogen reduced carbon dioxide using energy from ATP to make carbohydrates) occurs in the stoma
Chloroplasts are abundant in leaf cells, particularly in the palisade mesothelioma layer
Vacuole structure
The vacuole is surrounded by a membrane called the tonoplast and contains fluid
Vacuole function
- Only plant cells have a large permanent vacuole
- it is filled with water and solutes and maintains cell stability because when full it pushes against the cell wall, making the cell turgid
- if call the plant cells are turgid then this helps to support the plant, especially in non woody plants
Lysosomes structure
Small bags formed from the Golgi apparatus. Each is surrounded by a single membrane
- they contain powerful hydrolytic (digestive) enzymes
- they are abundant in phagocytise cells such as neutrophils and macrophages (types of white blood cell)that can ingest and digest invading pathogens such as bacteria
Function of lysosomes
- keep the powerful hydrolytic enzymes separate from the rest of the cell
- lysosomes can engulf old cell organelles and foreign matter, digest them and return the digested components to the cell for reuse
Cilia and undulipodia structure
- stick out from the cell and are surrounded by the cell surface membrane
- each contain microtubules
- formed from centrioles
Function of cilia and undulipodia
- the epithelial cells lining your airways each have many hundreds of cilia that beat and move the band of mucus
- nearly all cell types in the body have one cilium that acts as an antenna. It contains receptors and allows the cell to detect signals about its immediate environment
Which organelles don’t have membranes:
Ribosomes
Centrioles
Cytoskeleton
Cell Wall
Ribosomes structure
- small spherical organelles about 20nm in diameter
- made of ribosomal RNA
- made in the nucleolus as 2 separate subunits which pass through the nuclear envelope into the cell cytoplasm and then combine
- some remain free in the cytoplasm and some attach to the endoplasmic reticulum
Ribosomes function
- Ribosomes bound to the exterior or RER are mainly for synthesising proteins that will be exported outside the cell
- ribosomes that are free in the cytoplasm, either singly or in clusters, are primarily the site of assembly of proteins that will be used in the cell
Centrioles structure
The centrioles consist of two bundles of microtubules at right angles to each other. The microtubules are made of Tubulidentata protein subunits and are arranged to form a cylinder
9x3 arrangement
Centrioles function
- before a cell divides, the spindle, made of threads of tubular forms from the centrioles
- chromosomes attach to the middle part of the spindle and other proteins walk along the Tubulidentata threads, pulling the chromosomes to opposite ends of the cell
Centrioles are nvolved in the formation of cilia and undulipodia
- before the cilia form, the centrioles multiply and line up beneath the cell surface membrane
- microtubules then sprout outwards from each centriole, forming a cilium or undulopodium
What happens in the nucleolus
Ribosomes are made
What is the significance of chromosomes?
They contain the organism’s genes
Function of the nuclear envelope
Double membrane
Separates the contents of the nucleus from the rest of the cell
What do the pores in the nuclear envelope do?
They enable larger substances (eg mRNA) to leave the nucleus
Also allow substances to enter the nucleus eg from the cytoplasm
What is chromatin?
Genetic material consisting of DNA wound around histone proteins
Cell wall function
- contributes to the strength and support of the plant
- maintains cell shape
- permeable and allows solutions to pass through
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On a photomicrograh, why may 1 section be split up?
With electron microscopes sections must be cut out
9 steps for making and secreting a protein
- mRNA copy of the gene (instructions) for protein is made in the nucleus
- mRNA leaves the nucleus through pores
- mRNA attaches to a ribosome which is attached to the RER. Ribosome reads the instructions to assemble the protein
- Protein molecules are ‘pinched off’ in vesicles and travel to Golgi
- Vesicle fuses with Golgi
- Golgi processes and packages protein molecules for release
- Packaged insulin molecules are ‘pinched’ off in vesicles from Golgi and move towards plasma membrane
- Vesicles fuse with plasma membrane
- Plasma membrane opens to release protein molecules outside
How are prokaryotic cells similar to eukaryotic cells?
They both have:
- a plasma membrane
- a cytoplasm
- ribosomes
- DNA and RNA
How are prokaryotic cells different from eukaryotic cells?
- smaller
- much less well developed cytoskeleton with no centrioles
- don’t have a nucleus
- no membrane bound organelles eg RER
- cell wall made of peptidoglycan NOT cellulose
- smaller ribosomes
- DNA in cytoplasm not nucleus
Some prokaryotes also have:
Protective waxy capsule surrounding their cell walk
Plasmids
Flagella
Pili
Plasmids detailed
Small loops of DNA containing extra genes
What are flagella
Long whip like projections that rotate enabling them to move in liquids
Function of the nucleus
Control centre of the cell
Stores the organism’s genome
Transmits genetic information
Provides the instructions for protein synthesis
Cytoskeleton function
Provides strength and support to the cell
Holds organelles in place
Forms the track along which motor proteins transport organelles from one end of the cell to the other
Form the spindle for the movement of chromosomes
Organelles found in animal cells but not in plant cells
Centrosomes
Lysosomes
