Cells Flashcards
• Cell structure • Transport across cell membranes • Cell recognition and the immune system
What is the maximum resolution of a light microscope?
2x10^-7 m
What is the limitation with light microscopes?
The relatively long wavelength of light
What is the resolution of an electron microscope?
1x10^-10 m
What is the material put under the microscope called?
The object
What is the appearance of the object when viewed under a microscope called?
The image
What is the magnification?
How many times bigger the image is when compared to the object
How do you work out magnification?
Magnification = Size of image / Size of real object
What is the resolution of a microscope?
The minimum distance apart that two objects can be in order for them to appear as separate items
What is the resolving power of a microscope?
The minimum distance apart that two objects can be in order for them to appear as separate items
What does greater resolution do to an image?
Greater image clarity
What does greater magnification do to an image?
Increases the size of the image
What happens to the image if you increase magnification beyond the limit of resolution?
The image will be larger, but more blurred
What is cell fractionation?
The process where cells are broken up and the different organelles they contain are separated out
What three things must the solution in which the tissue is placed be for cell fractionation?
Cold
Isotonic
Buffered
Why must you use a cold solution to place the tissue in for cell fractionation?
To reduce enzyme activity that might break down organelles
Why must you use an isotonic solution to place the tissue in for cell fractionation?
To prevent organelles bursting or shrinking as a result of osmotic gain or loss of water
Why must you use a buffered solution to place the tissue in for cell fractionation?
So that pH doesn’t fluctuate
Why must the pH remain constant for cell fractionation?
Any change in pH could alter the structure of organelles or affect the functioning of enzymes
What are the two stages in cell fractionation?
Homogenation
Ultracentrifugation
What happens in homogenation?
Cells broken up by homogeniser Resultant fluid (homogenate) is filtered
Why are cells broken up by a homogeniser in homogenation?
To release the organelles from the cells
Why is the homogenate filtered in homogenation?
To remove any complete cells and large pieces of debris
What is ultracentrifugation?
The process by which fragments in the filtered homogenate are separated in a centrifuge
What does a centrifuge do?
Spins tubes of homogenate at very high speed in order to create a centrifugal force
In ultracentrifugation what speed do you start to spin at?
The lowest, working up to highest after removing the sediment/pellet
After a sample has been spun in a centrifuge, what is the fluid at the top of the tube called?
Supernatant
After a sample has been spun in a centrifuge, what is the layer at the bottom of the tube called?
The sediment or pellet
In ultracentrifugation, which part of the sample is spun again at a higher speed?
Supernatant
In animal cells, what are the first three organelles to form sediment (in order)?
Nuclei
Mitochondria
Lysosomes
In plant cells what are the first three organelles to form sediment (in order)?
Nuclei
Chloroplasts
Mitochondria
What is the speed of centrifugation that will cause nuclei to form the sediment?
1000 revolutions/minute
What is the speed of centrifugation that will cause mitochondria to form the sediment?
3500 revolutions/minute
What is the speed of centrifugation that will cause lysosomes to form the sediment?
16500 revolutions/minute
Why is cell fractionation important?
Allows scientists to study isolated components of cells
What are the two main advantages of an electron microscope?
High resolution
Beam can be focused using electromagnets
Why does an electron microscope have a high resolution?
The electron beam has a very short wavelength
Why can the electron beam in an electron microscope be focused using electromagnets?
Electrons are negatively charged
What has to be created within the chamber of an electron microscope in order for it to work properly?
A vacuum
Why does a vacuum have to be created in order for an electron microscope to work properly?
Electrons can be absorbed or deflected by molecules in air
What are the two types of electron microscope?
Transmission electron microscope (TEM)
Scanning electron microscope (SEM)
What is the resolution of a TEM?
0.1nm
What is the resolution of an SEM?
20nm
Why can a resolution of 0.1nm always be achieved with a TEM?
Difficulties preparing the specimen limit the resolution
A higher energy electron beam is required which could destroy the specimen
What are the main limitations of a TEM?
Whole system must be in a vacuum so living specimens cannot be observed
Complex staining process required (even then image isn’t in colour)
Specimen must be extremely thin
Image may contain artefacts
What are artefacts?
Things that result from the way that the specimen is prepared
What is a photomicrograph?
A picture taken of the image produced by a TEM on a screen
Why does a TEM produce a 2D image?
Specimens must be extremely thin
Why must specimens be extremely thin in order for them to be observed under a TEM?
So electrons can penetrate the specimen
How does a TEM form an image of a specimen?
Parts of the specimen absorb electrons and appear dark
Other parts allow electrons to pass through and so appear bright
What does a TEM consist of?
An electron gun that produces a beam of electrons
A condenser electromagnet that focuses the electron beam onto the specimen
What limitation of the TEM doesn’t apply to the SEM?
Specimens need to be extremely thin (not for SEM)
Why don’t specimens need to be thin for the SEM?
Electrons do not need to penetrate
How does the SEM direct an electron beam on the specimen?
From above onto the surface of the specimen, it is then passes back and forth across a portion of the specimen in a regular pattern
What happens to the electrons in an SEM?
The electrons are scattered by the specimen
What does the pattern of electron scattering in an SEM depend on?
The contours of the specimen’s surface
How can an SEM be used to produce a 3D image of a specimen?
Computer analysis of the pattern of scattered electrons and secondary electrons produced
What is used to measure the size of an object being observed under a light microscope?
Eyepiece graticule
What is needed to calibrate the eyepiece graticule?
Stage micrometer
How do you calculate the scale for different objective lenses?
By dividing the differences in magnifications
Cells have a specific internal structure to suit their functions. What is this known as?
Ultrastructure
What is the nucleus made up of?
Nuclear envelope Nuclear pores Nucleoplasm Chromosomes Nucleolus
What is the function of the nucleus?
Production of mRNA and tRNA (and hence protein synthesis)
Retain genetic information
Manufacture ribosomal RNA and ribosomes
What is the nuclear envelope?
A double membrane that surrounds the nucleus
What is the outer membrane of the nuclear envelope continuous with?
The endoplasmic reticulum
What is often found on the surface of the nuclear envelope?
Ribosomes
What is the purpose of the nuclear envelope?
Controlling entry and exit of materials in and out of the nucleus
Containing reactions taking place within the nucleus
On average how many nuclear pores are there in each nucleus?
Around 3000
Roughly how big are nuclear pores in diameter?
40-100nm in diameter
What is the purpose of nuclear pores?
Allowing the passage of large molecules (e.g. RNA) out of the nucleus
What is the nucleoplasm?
The granular, jelly-like material that makes up the bulk of the nucleus
What do chromosomes consist of?
Protein bound, linear DNA
What is the nucleolus?
A small spherical region within the nucleoplasm
What does the nucleolus do?
Manufactures ribosomal RNA and assembles to ribosomes
How many nucleoli are found in a nucleus?
There may be more than one
Roughly how big is a ‘normal’ nucleus?
10-20 micrometers in diameter
How long is a mitochondrion in length normally?
1-10 micrometers
What is a mitochondrion made up of?
Double membrane
Cristae
Matrix
What is the purpose of the double membrane around a mitochondrion?
To control the entry and exit of material to and from the mitochondrion
What is the inner membrane around a mitochondrion folded to form?
Extensions known as cristae
What are cristae?
Extensions of the inner membrane
What purpose do cristae serve?
Increasing surface area for the attachment of enzymes and other proteins required for respiration
What does the matrix do?
Makes up the rest of the mitochondrion
What is found in the matrix?
Proteins Lipids Ribosomes DNA Enzymes
What are the enzymes found in the matrix involved in?
Respiration
What does the DNA found in the matrix allow the mitochondrion to do?
Control the production of some of the mitochondrion’s own proteins
How many mitochondria are typically found in a cell?
It varies depending on the function of the cell
What cells will contain a large amount of mitochondria?
Cells that have a high level of metabolic activity
What are chloroplasts made up of?
Chloroplast envelope
Grana
Thylakoids
Stroma
What is the function of chloroplasts?
To carry out photosynthesis
What is the chloroplast envelope?
A double plasma membrane that surrounds the chloroplast
What is the function of the chloroplast envelope?
To be highly selective in what it allows to enter and leave the chloroplast
What are grana?
Stacks of up to 100 thylakoids
What takes place in the grana?
The first stages of photosynthesis (light absorption)
What is found in thylakoids?
Chlorophyll
What is chlorophyll?
The photosynthetic pigment
What do some thylakoids have?
Tubular extensions
If a thylakoid has a tubular extension, what does the extension do?
Join up with thylakoids in adjacent grana
What is the stroma?
A fluid filled matrix
What takes place in the stroma?
The second stage of photosynthesis (synthesis of sugars)
What can be found in the stroma?
A number of other structures (e.g. starch grains)
What does the fluid of the stroma possess?
All the enzymes required to make sugars in the second stage of photosynthesis
What do the granal membranes do?
Provide a large surface area
What attaches to the granal membrane?
Chlorophyll
Electron carriers
Enzymes required for the first stage of photosynthesis
How are chemicals attached to the granal membrane?
In a highly ordered fashion
Do all plant cells contain chloroplasts?
No
What do chloroplasts contain?
DNA and ribosomes
Why do chloroplasts contain DNA and ribosomes?
So chloroplasts can quickly and easily manufacture some of the proteins required for photosynthesis
What are the two type of endoplasmic reticulum?
Smooth endoplasmic reticulum (SER)
Rough endoplasmic reticulum (RER)
What is the endoplasmic reticulum?
An elaborate, 3D system of sheet-like membranes
Where is the endoplasmic reticulum found?
Spread through the cytoplasm of cells
What is the endoplasmic reticulum continuous with?
The outer nuclear membrane
What do the membranes in the endoplasmic reticulum enclose?
A network of tubules and flattened sacks called cisternae
What is the general structure of the rough endoplasmic reticulum?
Ribosomes present on outer surfaces of the membranes
What is the general structure of the smooth endoplasmic reticulum?
More tubular in appearance than the RER
No ribosomes on outer surfaces of membranes
What are the functions of the rough endoplasmic reticulum?
Provide a large surface area for the synthesis of proteins and glycoproteins
Provide a pathway for the transport of material (especially proteins) throughout the cell
What are the functions of the smooth endoplasmic reticulum?
Synthesise lipids Synthesise carbohydrates Store lipids Store carbohydrates Transport lipids Transport carbohydrates
What cells have a very extensive endoplasmic reticulum?
Cells that manufacture and store large quantities of lipids, proteins, and carbohydrates
What are cisternae?
Flattened membrane discs/sacks
What is the Golgi apparatus similar in structure to?
Smooth endoplasmic reticulum (but more compact)
What passes through the Golgi apparatus?
Proteins and lipids produced by the endoplasmic reticulum
What does the Golgi apparatus do to the proteins that pass through it?
Modifies the proteins (often by adding a non-protein group)
‘Labels’ the proteins
Why does the Golgi apparatus ‘label’ proteins?
To allow the proteins to be accurately sorted and sent to the correct destinations
What are regularly pinched off from the ends of the Golgi cisternae?
Golgi vesicles
What happens if Golgi vesicles move to the cell surface?
They fuse with the membrane and release their contents to the outside of the cell
Where are glycoproteins formed?
Golgi apparatus
What does the Golgi apparatus add to proteins to make glycoproteins?
Carbohydrates
What are the functions of the Golgi apparatus?
Form glycoproteins Produce secretory enzymes Secrete carbohydrates Transport, modify and store lipids Form lysosomes
Where is the Golgi apparatus especially well developed?
In secretory cells
When are lysosomes formed?
When Golgi vesicles contain enzymes (such as proteases and lipases)
What enzymes do lysosomes isolate from the rest of the cell?
Lysozymes
How many lysozymes can a lysosome contain?
As many as 50
Where do lysosomes release lysozymes?
Either to the outside of the cell or into a phagocytic vesicle within the cell
What are the functions of lysosomes?
Hydrolyse material ingested by phagocytic cells Exocytosis Autolysis Digest warn out organelles Apoptosis
What is exocytosis?
A process by which a cell transports secretory products through the cytoplasm to the plasma membrane
Why do lysosomes carry out exocytosis?
To destroy material around the cell
What is autolysis?
The process by which lysosomes cause a cell to self-digest itself from the inside out (often as a response to illness or injury)
What cells are most susceptible to autolysis?
Unhealthy cells
What is apoptosis?
Programmed cell death that occurs in specific biochemical steps leading to characteristic morphological changes
What are phagocytic cells?
Specialized cells that engulf and ingest other cells or particles
What is an example of a phagocytic cell found in vertebrates?
Phagocytes (specific type of white blood cells)
What is the function of a ribosome?
Protein synthesis
What are the two types of ribosome?
80S and 70S
Where are 80S ribosomes found?
Eukaryotic cells
Where are 70S ribosomes found?
Prokaryotic cells
Mitochondria
Chloroplasts
How big are 80S ribosomes?
About 25nm in diamater
How many subunits do ribosomes have?
2
What sub-units are ribosomes made up of?
One large sub-unit
One small sub-unit
What do the ribosomal sub-units contain?
Ribosomal RNA
Protein
How many types of ribosome are there?
2
What do cell walls consist of?
Cellulose microfibrils embedded in a matrix
What is the purpose of the cellulose microfibrils found in cell walls?
To contribute to the overall strength of the cell wall
What marks the boundary between adjacent cell walls?
The middle lamella
What cements adjacent cells together?
The middle lamella
What is the middle lamella?
A thin layer found in the cell wall
What are the functions of the cell wall?
Provide mechanical strength in order to prevent osmotic rupture
Give mechanical strength to the plant as a whole
Contribute to the movement of water along plants
How do cell walls contribute to the movement of water along plants?
By allowing water to pass along
What are the cell walls of algae made up of?
Cellulose or Glycoproteins or Cellulose & Glycoproteins
Do the cell walls of fungi contain cellulose?
No
What is chitin?
A nitrogen-containing polysaccharide
What are the cell walls of fungi made up of?
Chitin
Glycan
Glycoproteins
What is glycan?
A polysaccharide
What is a vacuole?
A fluid-filled sac bounded by a single membrane
What is the membrane around plant vacuole’s called?
The tonoplast
What does a plant vacuole contain?
A solution of: mineral salts, sugars, amino acids, wastes and pigments
What pigments can be found in a plant vacuole?
Anthocyanins
What functions do plant vacuoles serve?
Support for herbaceous plants and herbaceous parts of woody plants
Temporary food store
Attracting pollinating insects
How do plants vacuoles provide support?
By making cells turgid
How do plant vacuoles act as a temporary food source?
The sugars and amino acids they contain can be used as such
How do plant vacuoles attract pollinating insects?
The pigments they contain may colour petals to attract pollinating insects
What are similar cells grouped together to form?
Tissues
What are similar tissues grouped together to form?
Organs
What are similar organs grouped together to form?
Organ Systems
How do cells become specialised?
Controlled gene expression
Why are similar cells grouped together?
For working efficiency
What is an example of a tissue found in animals?
Epithelial tissue
What is an example of a tissue found in plants?
Xylem tissue
What is an organ?
A combination of tissues that are coordinated to perform various functions, often with a predominant major function
What tissues make up the stomach organ?
Muscle
Epithelium
Connective tissue