Cell structure Flashcards
How do light microscopes work?
By projecting light through a specimen, then focusing it with a series of lenses to magnify the image.
What is the equation for magnification?
Magnification = image size + object size
What will happen if you increase the magnification?
it may not be useful due to the lists of resolution of light
symbol for meters?
m
symbol for decimeters?
dm
symbol for centimeters?
cm
symbol for millimeters?
mm
symbol for micrometers?
um
symbol for nanometers?
nm
What must you do when using the magnification equation?
You must ensure that all the units are the same
What do you decimetre metres by to convert it into meters?
x10-1
What do you centimetre metres by to convert it into meters?
x10-2
What do you millimetre metres by to convert it into meters?
x10-3
What do you micrometer metres by to convert it into meters?
x10-6
What do you nanometre metres by to convert it into meters?
x10-9
What is resolution?
It is the ability to distinguish between 2 separate points. Increasing the resolution allows you to see more detail (unlike magnification which shows you the image at a bigger or smaller scale)
What is the laser scanning confocal microscope?
The still use a light beam to produce an image, but scan each object point by point, then use a computer to assemble the entire image. They produce good resolution and can be used at different depths on the specimen
How does an electrons microscope work?
It generates a beam of electrons with a wavelength 100, 000 times smaller than that of light. This means that they have maximum resolution of 0.2nm, allowing much smaller structures to be seen. The beam is focused with a series of magnets.
What are the two types of electron meters?
Transmission electron microscopes (TEM)
Scanning Electrons Microscopes (SEM)
What does the transmission electron microscope do?
They pass the beam of electrons through a prepared sample, producing a 2D image called an electron micrograph
The maximum magnification is x2,000,000 (possibly up to x50 million)
What does the scanning electrons microscope do?
They bounce the electron beam off of the sample, producing a 3D image.
The maximum magnification is x200,000
What are the advantages of electron microscopes?
Much higher magnification than light microscopes
Much higher resolution than light microscopes
Colour can be added later by computer software, producing false-colour micrographs which are easy to study
What are the disadvantages of electron microscopes?
Electron beams are stopped by air / water molecules, so the specimens must be dried out (killed) and placed in a vacuum
EMs are very expensive and difficult to prepare specimens for
What does the cell theory state?
All living things consist of cells
New cells can only be formed from the division of pre-existing cells
All cells contain information that instructs for the growth of that cell
Describe the plasma membrane
Description: Surrounds the cell. Has a fluid mosaic structure
Function: Selective barrier, retaining cell contents
Size: 7-10nm thick
Describe the rough endoplasmic reticulum (rough ER)
Description: intercellular membrane system cared with ribosomes
Function: Carries out protein synthesis due to the ribosomes. Intercellular transport
Size: variable
Describe the smooth endoplasmic reticulum (smooth ER)
Description: Intercellular membrane system without ribosomes
Function: synthesis of lipids (fats), including steroids
Size: variable
Describe the Golgi apparatus
Description: Specialised smooth ER. Consists of a stack of membrane-bound flattered sacs
Function: Modification and packaging of molecules such as glycoproteins, polysaccharides, hormones which are released by the rough ER
Size: variable
Describe the ribosomes
Description: Small, complex structures. Either attached to rough ER or free in cytoplasm
Function: carry out protein synthesis
Size: 25nm diametre
Describe the nucleus
Description: major cell organelle containing chromatin (DNA and histones)
Function: Regulates activities of cells. Carries hereditary information
Size: 20 um diametre
Describe the nuclear envolope
Description: double membrane surrounding nucleus, with nuclear pores
Function: Regulates exchange between nucleus and sutoplasm. Some Protein synthesis then continues into the Rough ER
Size: 2 x10 nm
Describe the nucleolus
Description: Specialised region of the nucleus, not surrounded by a membrane
Function: Synthesis of RNE and ribosomes
Size: 2 um diametre
Describe the mitochondria
Description: Double-membrane organelle containing enzymes on their surfaces for respiration folded inner membrane formes finger-like projections called cristal with a fluid in the spaces called the matrix
Function: carries out respiration to produce ATP
Size: 2-5 um diameter
Why may mitochondria look different?
- They may be seen in different sections
- They may have been damages during the reparation of he slide
- They may be of different ages
- They will vary in size naturally, even within the same cell
Describe the chloroplast
Description: plant cell organelle with double membrane. Inner membrane continuous with flattened membrane sacs called thylakoids. A stack of these is called a grain. They are connected by lamellae. The fluid filled region in the middle is called the storm. It may contain a number of starch grains or lipid droplets
Function: carries out photosynthesis - chlorophyll molecules on the inner membrane capture sunlight, which is used to make carbohydrates from water and CO2
Size: 4-10 um
Describe the cell wall
Description: Plant structure of cellulose mircofibrils
Function: Support and protection of the ell
Size: 5 micrometers thick
Describe the lysosome
Description: Spherical membrane - bound vesicles containing enzymes
Function: carries out intercellular digestion
Size: 50nm diameter
Describe the vacuole:
Description: it is surrounded by a membrane called tonoplast, and contains fluid
Function: Helps support the plant
Size: variable
Describe the Flagella and Celia
They re hair like extensions from which the surface of the cell. Each one is made up of a ring of 9 microtubules, with 2 microtubules in the center - called a 9 + 2 arrangement
Where is flagella found and what is its function
It is usually fund in ones or twos on a cell and are much longer than Celia.
They can be used to move a cell around
e.g. bacteria often have the (although microtubules arrangement is different)
Where is Celia found and what is its function
Usually found in large numbers on the cell surface and around 10um long. They sweep substances across the cell surface
e.g. eggs in the oviduct
mucus in the trachea
What is the cytoskeleton and what does it do?
The are a network of rotten fibres found in all cells, which provide an internal framework ro keep the cell’s shape
What are the main fibres in cytoskeleton calles, and what are they?
They are called, microtubes, which are cylinders of protein called tumbling and are 25nm in diameter.
What can microtubes be used for?
It can be used to move a micro-organism through a liquid or to move organelles around inside the cell.
e.g.
They form centrioles, which move chromosomes during mitosis
They help vesicle move from the endoplasmic reticulum to the Golgi apparatus
The proteins which cause the movement are called mirotuble motor, and use energy (ATP) to drive the movements
Each different organelle has a …….. …….. within the cell. This is called a ……. …. ……, as each organelle contribute to the overall survival of the cell
specific function
division of labour
What are the two cell groups?
Eukaryotic and prokaryotic
Describe prokaryotic cells and how they differ from prokaryotic cells
They are bacteria which do not have a separate nucleus, or any member bound organelles
They are are much smaller than eukaryotic cells.
There DNA is ‘naked’ as it is not wound around portions called histones
Some structures are common to all prokaryotic cells but others are only found in some species
Can you find a nucleus in eukaryotic/prokaryotic cells
Eukaryotic: Usually present (surrounded by a nuclear envelope and containing nucleolus)
Prokaryotic: NO
Can you find a mitochondria in eukaryotic/prokaryotic cells
Eukaryotic: usually present
Prokaryotic: NO
Can you find a rough ER and smooth ER) in eukaryotic/prokaryotic cells
Eukaryotic: always
Prokaryotic: NO
Can you find a ribosomes in eukaryotic/prokaryotic cells
Eukaryotic: Yes, relatively large
Prokaryotic: Yes, relatively small
Can you find a cytoskeleton in eukaryotic/prokaryotic cells
Eukaryotic: Always
Prokaryotic: NO
Can you find chromosome in eukaryotic/prokaryotic cells
Eukaryotic: Yes, DNA arranged in several long strands, associated with histones
Prokaryotic: Yes, DNA circular
Can you find a cell wall in eukaryotic/prokaryotic cells
Eukaryotic: Yes, in plants
Prokaryotic: Always, made up of peptidoglycan
Can you find cilia and flagella in eukaryotic/prokaryotic cells
Eukaryotic: Sometimes
Prokaryotic: Some flagella
Can you find chloroplast in eukaryotic/prokaryotic cells
Eukaryotic: Present in some plant cells
Prokaryotic: NO
What structure contains RNA and not DNA?
ribosomes
What is the maximum magnification of a light microscope?
x1500
What is the maximum resolution for a light microscope?
200 nm
What is the maximum magnification of a TEM?
x2 million
Convert 0.15 micrometres into nanometres
150nm
Which process involves mRNA instructions being used to create proteins at the ribosomes?
translation
Why do we need staining for light and electron microscopes?
- Very high contrast. The stain absorbs electrons in much higher amounts than the surrounding medium. Therefore, different regions of the sample have different electron densities and can be differentiated easier in the resulting projections.
- The radiation damage from the absorbed electrons is mostly irrelevant because it does not affect stain salts at the same rate as the organic molecules of the sample.
- The sample is easy to prepare. Generation of a negative stained grid takes less than four minutes and no fancy apparatus.
Describe the structure and functions of centrioles
Structure: They consists of two bundles of microtubes at right angles from each other. the microtubules are made of tubulin protein subunits and are arranged to fork a cylinder.
Function: The main function of the centriole is to help with cell division in animal cells.
Celiogenesis is simply the formation of cilia and flagella on the surface of cells. Before the cilia is formed the centrioles multiply and line up beneath the cell surface membrane. Microtubules then sprout outwards from each centriole, forming a cilium or undulipodium
Why si the cytoskeleton important?
It forms a framework for the movement of organelles around the cytoplasm - most of the organelles are attached to the cytoskeleton. The network consists of protein microfilaments, intermediate filaments, and microtubules. The cytoskeleton provides an important structural framework for: Cell shape
