Cells Flashcards
What is resolution?
The minimum distance two objects have to be in order to be seen as separate items.
Increasing magnification doesn’t always increase resolution.
This basically means his clear the image is.
What is cell fractionation?
Process where the cells are broken up and the different organelle are separated out.
This takes place in a cold (reduces enzyme activity), same water potential (prevents damage due to osmosis), buffered (pH doesn’t fluctuate) solution.
What is homogenation?
Cells are broken down by a homogeniser.
This releases organelle from cells.
This resultant fluid known as homogenate is then filtered to remove whole cells and large debris.
What is ultracentrifugation?
This is the process by which the fragments in the filtered homogenate are separated in a machine called centrifuge.
This spins tubes of homogenate at a very high speed to create a centrifugal force.
Heaviest organelle fall at smaller speeds to force a pellet leaving a supernatant.
The process repeats from the removed supernatant.
Advantages of a light microscope?
Cheap
Live specimen
Easy staining process
Disadvantages of light microscopes?
Poor resolution due to long wave length of light. Poor magnification. 2D. Image must be drawn. Artefacts.
How does a transmission electron microscope work?
Electron gun produces a beam of electrons which is focused onto specimen by a condenser electromagnet.
This is sent through a thin slice of specimen.
Sections of absorbed electrons will appear dark and where they pass will appear bright.
An image is produced on the screen and photographed to produce a photomicrograph.
Advantages of a transmission electron microscope?
High resolution (0.1nm) as electrons have a short wave length. High magnification.
Disadvantages of transmission electron microscope?
Vacuum required Complex staining process Black and white Specimen must be extremely thin Artefacts High electron beam may destroy specimen Expensive
How does the scanning electron microscope work?
SEM directs the beam of electrons above the specimen and onto its surface.
The beam is passed back and forth across the specimen in a regular pattern.
Electrons are scattered by the specimen, this depends on its contours.
A 3D image is built up on the computer.
Advantages of a scanning electron microscope?
3D image Resolving power of 20nm High magnification Coloured image Specimen not cut thin Unlikely to have artefacts
Disadvantages of scanning electron microscope?
Vacuum so no live specimen
Complex staining process
Expensive
What is a stage micrometer?
A slide that had a scale etched onto it.
This is used to calibrate the eyepiece graticule.
Usually the scale is 2mm and the subdivisions are 0.01mm.
What is an eyepiece graticule?
Glass disc that is placed on the eyepiece and has a scale etched onto it.
This scale is usually 10mm and had 100 subdivisions.
How to calibrate the eyepiece graticule?
Units on the micrometer must be equal to the units on the graticule scale.
Describe nucleus’ structure.
10-20um in diameter Nuclear envelope Nuclear pores Nucleoplasm Chromosomes Nucleolus
What are the functions of the nucleus?
Control centre of the cell.
Retain genetic material.
Manufactures ribosomal RNA and ribosomes.
Describe the structure and function of the nuclear envelope.
Double membrane that surrounds the nucleus.
The outer membrane is continuous with endoplasmic reticulum of the cell and often had ribosomes on its surface.
It controls the entry and exit of materials in and out of the nucleus.
Describe the function and structure of the nuclear pores.
Nuclear pores allowed the passage of large molecules such as messenger RNA.
There are typically around 3000 pores in each nucleus each 40-100nm in diameter.
What is the nucleoplasm?
Nucleoplasm is the granular, jelly like material that makes the bulk of the nucleus.
What are chromosomes?
They consist of protein bound linear DNA.
Describe the structure and function of the nucleolus.
Small spherical region within the nucleoplasm.
Manufactures ribosomal RNA and assembles the ribosomes.
There can be more than one within a nucleus.
Describe the structure of the mitochondrion.
Mitochondria are usually rod shaped and 1-10um in length.
Around the organelle is double membrane that controls the entry and exit of material.
The inner of two membranes are folded to form extensions.
What is the Cristae within the mitochondrion?
Extension of inner membrane, which in some species extend across the whole length.
These provide high surface area for attachment of enzymes and proteins needed for respiration.
What is the matrix within him the mitochondrion?
The matrix makes up the remainder of the mitochondrion.
It contains proteins,lipids, ribosomes and DNA to control the production of their own proteins.
Many enzymes are found here.
Describe the structure and function of the chloroplast.
Organelle which carry out photosynthesis.
Typically disc shaped, 2-10um in length.
Made up of chloroplast envelope, the grana and the stroma.
What is a chloroplast envelope?
Double plasma membrane that surrounds the organelle.
It is highly selective in what it allows to enter and leave the chloroplast.
What is the grana within the chloroplast?
Stacks of up to 100 disc like structure called thylakoids within these there is the pigment chlorophyll.
This is where the first stage of photosynthesis (light absorption) takes place.
What is the stroma within the chloroplast?
Fluid filled matrix where the second stage of photosynthesis (synthesis of sugar) takes place.
There is a number of other structure such as starch grains.
Describe the function and structure of the rough endoplasmic reticulum.
Ribosomes present on the outer membrane.
Provides a large surface area for synthesis is of proteins and glycoproteins.
Provide a pathway for the transport of materials, especially proteins through a cell.
Describe the structure and function of the smooth endoplasmic reticulum.
Lacks ribosomes on the surface and often looks more tubular.
It’s function is to synthesise, store and transport lipids and carbohydrates.
What’s the structure of Golgi apparatus?
It consists of a stack of membranes that make up flattened sacs or cristernae, with small round hollow structures called vesicles.
Functions of the Golgi apparatus.
Adds carbohydrates to proteins to form glycoproteins. Produce secretary enzymes. Secrete carbohydrates. Transport, modify and store lipids. Form lysosomes.
What are lysosomes?
Form when vesicles of Golgi apparatus contain enzymes.
These enzymes can hydrolyse the cell walls of a bacteria.
As many as 50 enzymes can be found here.
Release enzymes to the outside of the cell.
Digest worn out organelle.
Completely digest the cell once dead.
Describe the structure and function of the ribosome.
Small cytoplasm granule found in all cells in the cytoplasm or associated with the RER.
Have 2 subunits, large and small each containing RNA and protein.
80S are eukaryotic cell 25nm.
70S are prokaryotic, found in both mitochondria and chloroplasts.
Describe the function and structure of the cell wall.
Consists of polysaccharide cellulose embedded in the matrix.
Provide mechanical strength in order to prevent the cell from bursting from osmotic pressure.
Allows water to pass along it and contribute to movement.
Describe the vacuole.
A fluid filled sac bound by a single membrane (tanoplast).
Contains salts, sugars, amino acids and waste.
Makes cell turgid.
Food store.
What is epithelial tissue?
Found in animals and consists of sheets of cells.
Line surfaces of organs and often have protective or secretory function.
What does the digestive system do?
Digests and processes food.
What does the respiratory system do?
Used for breathing and gas exchange.
What does the circulatory system do?
Pumps and circulates blood.
What is a eukaryotic cell?
Large. Have nucleus. Membrane bound organelle. Ribosomes are 80S. Cell wall is made up of cellulose.
What’s a prokaryotic cell?
No nucleus. Plasmids present. No membrane bound organelle. Ribosomes are 70S. Cell wall made up of murein.
Describe the structure of a bacteria cell.
PROKARYOTIC.
0.1-10um in length.
Simple structure.
Food stored as glycogen granules and oil droplets.
Cell wall made of Murein.
Capsule used for attachment and protection.
Ribosomes are 70S.
Strand of single strand circular DNA and plasmids.
Flagellum for movement.
Cytoplasm.
Describe the structure of a virus.
20-300nm. Acellular and nonliving. Attachment protein. Lipid envelope. Matrix. Caspid. Enzyme and Genetic material.
What is mitosis?
Produces 2 daughter cells that have the same number of chromosomes as the parent cell and eachother.
What is meiosis?
Produces 4 daughter cells, each with half the number of chromosomes as the parent cell.
What are the stages of mitosis?
Prophase. Metaphase. Anaphase. Telophase. Cytokinesis.
What is prophase in mitosis?
Chromosomes shorten and thicken.
Centrioles move to either pole of the cell.
Spindle fibres form.
The nucleolus disappears and the nuclear envelope breaks.
Chromosomes are drawn to the equator by spindle fibres.