Eukaryotic Cells Flashcards
1
Q
Who put together one of the first working optical microscopes?
A
Robert Hooke
2
Q
What does cell theory state?
A
That cells are a fundamental unit of structure, function and organisation in all living organisms
3
Q
What are the two types of microscope and what is their magnification?
A
- the light microscope/ optical microscope. It can magnify up to 1500 times
- the electron microscope: can give a magnification of up to 500 000 times
4
Q
How does a light microscope work?
A
A specimen or thin slice of biological material is placed on the stage of the light microscope and illuminated from underneath, either by sun light reflected with a mirror or by a built-in light source. The objective lens produces a magnified and inverted image, which the eyepiece lens focuses at the eye
5
Q
How do you calculate the total magnification kf a light microscope?
A
Magnification of objective lens x maginfication of eyepiece lens = total magnification
6
Q
How will most of the specimens in a light microscope be prepared?
A
Most of them will be dead, stained, specially preserved and sectioned (very thinly sliced) before they are mounted on a slide. However you can look at living organisms, tissue and cells
7
Q
Staining a specimen is used to make it to identify particular types of cell or particular parts of the cell under the microscope. What are some of the stains used and what do they stain?
A
- haematoxylin - stains the nuclei of plant and animal cells purple, blue or brown
- methylene blue - stains the nuclei of animal cells blue
- acetocarmine - stains the chromosomes in dividing nuclei in both plants and animals
- iodine - stains starch containing material in plant cells blue-black
8
Q
What are the advantages and disadvantages of a light microscope?
A
• advantages:
- can see living plants and animals or parts of them directly. This is useful and allows you to compare prepared slides with living tissue
- relatively cheap so are available in schools and universities, hospitals, industrial labs and research labs
- relatively light and portable so we can use them anywhere
• disadvantages:
- preserving and staining tissue can produce artefacts in the tissues being observed, so what we see may be the result of preperation rather than a true representation of the living tissue
- limited powers of resolution and magnification
9
Q
How do electron microscopes work?
A
- uses a beam of light to form an image
- the electrons are scattered by the specimen in much the same way as light is scattered in a light microscope
- in an electron microscope the electrons effectively behave like light waves with a very tiny wavelength
- electromagnetic or electrostatic lenses focus the electron beam to form an image.
- resolving power increases as the wavelength gets smaller so electron microscopes can resolve detail down to less than 0.00001 um
- for it to work the specimens have to be in a vacuum
10
Q
What does the preperation of a specimen for an electron microscope involve?
A
• the specimen has to be dead as it takes place in a vacuum
• involves:
- chemical preservation
- freeze drying
- freeze fracturing
- removing the water (dehydration)
- embedding
- sectioning
- mounting on a metal grid
• specimens are often stained using heavy metals such as uranium and lead. This is to improve the scattering of the electrons and make greater contrast in the image making it clearer and easier to interpret
• the image is displayed on a monitor or computer screen
11
Q
What are the two main types of electron micrographs and what are their differences?
A
- transmission electron micrographs (TEMs): they are 2D
* Scanning electron micrographs (SEMs) have lower maginfication but are 3D and can be very striking
12
Q
What is added after the image has been taken on an electron micrograph and why?
A
False colours to make it easier to identify different cells. They are not stains
13
Q
What are the advantages and disadvantages of using electron microscopes?
A
• advantages:
- huge powers of magnification and resolution
• disadvantages:
- all specimens are examined in a vacuum (air would scatter the electrons and make the image of the tissue fuzzy) so it is impossible to look at living material
- specimens undergo severe treatment that is likely to result in artefacts. Preparing specimens for the electron microscope is very skilled work
- very expensive
- large, have to be kept at a constant temperature and pressure and need to maintain an internal vacuum
14
Q
What is maginfication
A
A measure of how much bigger the image you see is than the real object
15
Q
What is resolution (resolving power)?
A
A measure of how close together two objects are before they are seen as one
16
Q
What are eukaryotes?
A
Cells with genetic material contained in a membrane bound nucleus and a number of other membrane bound organelles
17
Q
What membranes do prokaryotes have?
A
Cell surface membrane
18
Q
What does the cell surface membrane (outer cell membrane) do?
A
Forms the boundary of all cells controllint what passes into and out of the cell and allowing the fluids either side of it to have different compositions
19
Q
What do membranes within cells make possible?
A
To have the right conditions for a particular reaction in one part of the cell and different reactions to suit other reactions somewhere else in the same cell
20
Q
What functions do membranes perform apart from the controlling of substances in and out?
A
- many chemical processes take place on membrane surfaces. The reactions of respiration take place on the inner mitochondrial membrane. Enzymes and other factors are held closely together so the reaction can proceed smoothly
- the cell surface membrane is flexible to allow the cell to change shape very slightly as its water content changes or dramatically e.g. when a white blood cells engulfs a bacterium
- chemical secretions made by the cells are packaged into membrane bags called vesicles so some membranes must be capable of breaking and fusing together readily
21
Q
What is the membrane mainly made up of?
A
Lipids and proteins
22
Q
What type of lipids exist in the membrane?
A
Polar lipids. They are lipid molecules with one end joined to a polar group
23
Q
Many of the polar lipids in the membrane are phospholipids. How do they form a unit membrane?
A
With water or aqueous solution on either side they form a bilayer with their hydrophillic heads pointing into the water while the hydrophobic tails stay protected in the middle
24
Q
What molecules does a lipid-bilayer allow in?
A
Fat-soluble organic molecules
25
Ionic molecules are needed in cells but these can not pass through lipids. How do they get in?
Because the cell membrane also consists or proteins and other molecules
26
What is the fluid mosaic model?
• the model of the floating proteins (like icebergs) in a lipid sea
27
What affects how freely proteins float about in the membrane?
The proportion of phospholipids containing unsaturated fatty acids. The more unsaturated fatty acids the more fluid in the membrane
28
How are proteins arranged in the membrane?
* many have a hydrophobic part which is buried in the lipid bilayer and a hydrophilic part whicn can be involved in a variety of activities
* some proteins penetrate all the way through the lipid whilst others only go part of the way through the bilayer
29
How do membrane proteins help substances move across the membrane?
* the proteins form pores or channels, some permanent and some temporary that allow specific molecules to move through
* some of these channels can be open or shut depending on the conditions in the cell. These sre known as gated channels
* some of the protein pores are active carrier systems using energy to move molecules
* other protein pored are gaps in the lipid bilayer that allow ionic substances to move through the membrane in both directions
30
Proteins may act as specific receptor molecules on membranes. What does this mean and give an example
They make cells sensitive to a particular hormone
They may be enzymes, particularly on any internal cell membranes, to control reactions linked to that membrane
31
What are the cytoplasm and nucleus called together?
The protoplasm
32
What are the structures that can onlt be observed in detail using the electron microscope known as?
The ultrastructure of the cell
33
How are membranes important and what do they do?
* they are important both as an outer boundary to the cell and in the multitude of internal membranes
* they localise enzymes in reaction pathways e.g. respiration in mitochondria and photosynthesis in chloroplasts
* they compartmentalise chemicals, for example hydrolytic enzymes in lysosomes
34
What is the Cytoplasm
A jelly like liquid containing what is needed to carry out rhe day-to-day tasks of living
35
What is the structure of the nucleus?
* it is the largest organelle in the cell and can be seen with a light microscope
* it is usually spherical in shape and surrounded by a nuclear double membrane containing holes or pores, known as the nuclear envelope
* inside the nuclear envelope the two main substances are the nucleic acuds and proteins
* there is at least one nucleolus- an extra dense area of almost pure DNA and protein. It is involved in the production of ribosomes
36
How can the nucleus control events in the cytoplasm?
Because chemicals can pass in and out of the nucleus through the pores
37
When the cell is not actively dividing what is happening in the nucleus?
the DNA is bonded to the protein to form chromatin which looks like tiny granules
38
What does mitochonrion mean and what does it describe?
* 'thread granule'
* describes the tiny rod- like structures that are 1um wide by up to 10 um long and seen in the cytoplasm of all eukaryotic cells under the light microscope
39
What happens at the mitochondria?
* they are the powerhouses of the cell
* here in a series of complicated biochemical reactions, simple molecules are oxidised in the process of cellular respiration producing ATP that can be used to drive the other functions of the cell
40
What information does the number of mitochondria present in a cell give you?
Useful information about the function of the cell. Cells that require very little energy have few mitochondria and cells with an energy demanding function contain a large number of mitochondria
41
What is the structure of the mitochondria?
• they have an outer and inner membrane that surround it
• they contain their own genetic material so that when the cell divides the mitochondria replicate themselves under the control of the nucleus
• they have an internal arrangement adapted for their function:
- the inner membrane is folded to form cristae which give a large surface area surrounded by a fluid matrix
- this structure is closely integrated with the events in cellular respiration that take place in the mitochondrion
42
What is the endosymbiotic theory of the evolution of eukaryotic cells?
Due to the fact that they have their own DNA scientists think that mitochondria and chloroplasts originated as symbiotic eubacteria living inside early cells and over millions of years of evolution they have become an integral part of the cell
43
What are the centrioles?
* in each cell there is usually a pair of centrioles near the nucleus
* Each centriole is made up of a bundle of nine tubules and is about 0.5 um long by 0.2 um wide
* the centrioles are involved in cell division
* when a cell divides, the centrioles pull apart to produce a spindle of microtubules that are involved in the movement of the movement of the chromosomes
44
What is the structure of the cytoskeleton?
* It is a 3D web like structure that fills the cytoplasm
| * it is made up of microfilaments which are protein fibres and microtubules (tiny protein tubes about 20 nm in diameter
45
Where are microtubules found and what do they consist of?
They are found both singly and in bundles throughout the cytoplasm. They consist mainly of the globular protein tubulin
46
What functions does rhe cytoskeleton perform?
* it gives the cytoplasm structure
* keeps the organelles in place
* many of the proteins in the microfilaments are related to actin and myosin, the contractile proteins in the muscle and the cytoskeleton is closely linked with cell movements and transport within cells
47
What are vacuoles in animal cells and when are they used?
* they are not a permenant feature
* they are membrane lined enclosures that are formed and lost as needed.
* many simple animals make vacuoles around the prey they engulf
* white blood cells form similar vacuoles around engulfed pathogens
* contractile vacuoles are an important feature in simple animals that live in fresh water because they allow the water content of the cytoplasm to be controlled
48
What is the endoplasmic reticulum (ER) and what does it do?
* a 3D network of cavities bounded by membranes
* some of the cavities are sac like and some are tubular
* the ER spreads extensively through the cytoplasm.
* the ER network links with the membrane around the nucleus and makes up a large part of the transport system within a cell as well as being the site of synthesis of many important chemicals
49
What different methods have been used to work out the funtion of the ER?
* electron microscopes have shown up the different forms: the rough and smooth endoplasmic reticulum
* cells can also be provided with radioactively labelled chemicals that are building blocks for specific molecules, e.g. labelled amino acids for the synthesis of proteins and find out where they appear in the cell. The labelled products can be tracked using microscopy another method of locating them is to break the cells open and then spin the contents in a centrifuge. The different parts of the cell can be seperated out and the regions containing the radioactively labelled substances identified
50
What are the main type of ribosomes in eukaryotic cells?
* 80s ribosomes. The s stands for Svedberg
* when 80s ribosomes are broken into their two units they are made up of a 40S small subunit and a 60S large subunit
* the ratio of RNA: protein in 80S ribosomes is 1:1
51
What other type of ribosome are found in the mitochondria and chloroplasts of the plant cells that are often found in prokaryotic cells?
* 70S ribosomes
* they are made up of a small 30S subunit and a larger 50S subunit
* the ratio of RNA: protein in 70S ribosomes is 2:1
52
What is the rough endoplasmic reticulum?
* it is covered in granules (80S ribosomes)
* the function of the ribosomes is to make proteins and the RER isolates and transports these proteins once they have been made
* the RER has a large surface area for the synthesis of all these proteins and it stores and transports them both within the cell and from the inside to the outside
* cells that secrete materials such as those producing the digestive enzymes in the lining of the gut have a large amount of RER
53
What is an example of exocytosis?
Some proteins such as digestive enzymes and hormones are not used inside the fell that makes them so have to be secreted without interfering with the cell's activites
54
What is smooth endoplasmic reticulum (SER)
* it is involved in synthesis and transport but jn this case of steroids and lipids
* lots of SER is found in the testes which makes the steroid hormone testosterone and in the liver which metabolises cholesterol amongst other lipids
55
What does the amount and type of endoplasmic reticulum in a cell do?
Gives an idea of the type of job the cell does
56
What is the structure of the golgi apparatus?
It is made up of stacks of parallel, flattened membrane pockets called cisternae, formed by vesicles from the endoplasmic reticulum fusing together
57
How have scientists tried to find out what the golgi apparatus does?
Materials have been radioactively labelled and tracked through the cell to try and find out exactly what goes on inside it
58
What happens in the golgi apparatus?
* proteins are brought to the golgi apparatus in vesicles that have pinched off from the RER where they were made
* the vesicles fuse with the membrane sacs of the golgi apparatus and the protein enters the golgi stacks
* as the proteins travel through the golgi apparatus they are modified
* carbohydrate is added to some proteins to form glycoproteins such as mucus
* the golgi apparatus is also involved in producing materials for plant and fungal cell walls and insect cuticles
* some proteins in the golgi apparatus are digestive enzymes. These may be enclosed in vesicles to form an organelle known as a lyosome.
* alternatively enzymes may be transported through the golgi apparatus and then in vesicles to the cell surface membrane where the vesicles fuse with the membrane to release extracellular digestive enzymes
59
Who first observed the golgi apparatus?
Camillo Golgi
60
How has the golgi apparatus been observed?
* the electron microscope has helped to show the internal structure of the golgi apparatus
* by labelling specific enzymes so they can be seen using the electron microscope
61
What are the differences in the molecules contained in the outer and inner areas of the golgi apparatus?
* the inner areas of the golgi apparatus nearer to the RER have shown to be very rich in enzymes that modify proteins in various ways. This is where most enzymes or membrane proteins are converted into the finished product
* in the outer regions of the golgi apparatus you find lots of finished protein products but not many enzymes that make them
62
How are areas of the protein that need to be on the outside of the cell membrane made sure they are facing the right direction?
They are orientater by the golgi apparatus so when they arrive at the membrane they are inserted facing in the right direction
63
What are lysosomeszm
Dark spherical bodies in the cytoplasm of most cells that contain a powerful mix of digestive enzymes and destroy the organelles in the cells of your body that are worn out
64
How do lysosomes work and what do they do?
* they frequently fuse with eachother and with a membrane bound vacoule containing either food or an obsolete organelle
* their enzymes then break down the contents into molecules that can be used.
* a lysosome may fuse with the outer cell membrane to release its enzymes outside the cell as extracellular enzymes for example to destroy bacteria or in digestion
65
What is apoptosis?
* when lysosomes self destruct
* if an entire cell is wearing out, needs to be removed during development, has a mutation or is under stress its lysosomes may rupture, releasing their enzymes to destroy the entire contents of the cell
66
A plant cell has most of the same organelles as an animal cell. What are the orgnalles they have that animal cells do not?
* permenant vacuoles
| * chloroplasts
67
Draw an animal cell
Look at snap camera roll
68
Draw a plant cell
Snapchat camera roll
69
Why are plant cells more regular and uniform in their appearance?
Because each cell is bounded by a cell wall
70
Give the features of a plant cell wall
* it is largely made up of insoluble cellulose
* it is usually freely permeable to everything that is dissolved in water
* however it can become impregnated with suberin in cork tissues or with lignin to produce wood. These compounds affect rhe permeability of the cell wall
71
How does a cellulose cell wall form?
* it consists of several layers
* the middle lamella is the first layer to form when a plant cell divides. It is made largely of pectin, a polysaccharide that acts like glue and holds the cell wall of neighbouring plant cells together. Pectin has lots of negatively charged carboxyl groups and these combine with positive calcium ions to form calcium pectate. This binds to the cellulose that builds up either side
* the cellulose microfibrils and the matrix build up on either side of the middle lamella.
* to begin with these walls are very flexible with the cellose microfibrils all orientated in a similar direction. These are the primary cell walls
* as the plant ages thickening may take place. A secondary cell wall builds up with the cellulose microfibrils laid densely at different angles to eachother. This makes the composite material more rigid. Hemicelluloses harden it further.
* in some plants, particularly woody perennials, lignin is then added to the cell walls to produce wood, which makes the structure even more rigid.
* within the structure of a plant there are many long cells with cellulose cell walls that have been heavily lignified. These are known as plant fibres
72
What does intracellular exchange take place through?
Special cytoplasmic bridges between the cells known as the plasmodesmata
73
How are the plasmosdemata formed and how do they work?
* they are produced as the cells divide. They do not seperate fully and threads of cytoplasm remain between them
* these threads pass through gaps in the newly formed cells walls and signalling substances can pass from one cell to another through the cytoplasm
* the interconnected cytoplasm of the cells is known as symplast
74
Describe the features of the permenant vacuole in plants
* a vacuole is any fluid filled space inside the cytoplasm surrounded by a membrane
* it can occupy up to 80% of the volume of the whole plant cell
* it is surrounded by a specialised membrane called the tonoplast
* the tonoplast has many different protein channels and carrier systems in it. It controls the movements of substances into and out of the vacuole and so controls the water potential of the cell.
* the vacuole is filled with cell sap, a solution of various substances in water
* this solution causes water to move into the cell by osmosis and as a result the cytoplasm is kept pressed against the cell wall. This in turn keeps the cell turgid. Very high pressures can be developed this way
75
What are the functions of the vacuoles in plants?
* they maintain the plant cell shape
* they are used for the storage of a number of different substances
* many vacuoles store pigments
* vacuoles can store proteins in the cells of seeds and fruits
* some plants have vacuoles which contain lytic enzymes and have a function rather like lysosomes in animal cells
* they often store waste products and other chemicals
76
Which plant cells contain chloroplasts?
* only those in the green parts of the plant
* however almost all plant cells contain the genetic information to make chloroplasts and so in some circumstances different areas of the plant will become green and start to photosynthesise
* the exceptions are parasitic plants
77
What are the similarities and differences between mitochondria and chloroplasts?
They both:
- are large organelles, have a bioconvex shape with a diameter of 4-10 um and are 2-3um thick
• contain their own DNA
• Are surroundes by an outer surface membrane
• have an enourmously folded inner membrane that gives a greatly increased surface area on which enzyme-controlled reactions take place
• are thought to have been free-living prokaryotic organisms that were engulfed by and became part of other cells at least 2000 million years ago
However chloroplasts:
• are the site of photosynthesis
• contain the green pigment chlorophyll which je largely responsible for trapping the energy from light
• are formed from a relatively unspecialised plant organelle known as a leucoplast
78
What are amyloplasts?
* a specialised plant organelle that develops from leucoplasts
* they are colourless and store starch
* the starch can be converted to glucose and used to provide energy for when the cell needs it
* amyloplasts are found in large numbers in areas of a plant that store starch
79
What are specialised cells organised into?
Tissues which are then organised into organs
80
What are tissues?
Groups of similar cells that all develop from the same kind of cell
81
What are the four main tissue types in the human body?
* epithelial
* connective
* muscle
* nervous
82
What are the features of epithelial tissue?
* they are tissues that form the lining of surfaces both inside and outside your body
* they all rest upon an extracellular basement membrane
* cells in epithelial tissues usually sit together and form a smooth surface that protects the cells and tissues below
83
What are the different types of epithelial tissue?
* simple squamous
* cuboidal
* columnar
* ciliated
* gladular
* compound stratified
84
What is squamous epithelium?
* commonly found lining the surfaves of blood vessels
| * forms the walls of the capillary and the lining of the alveoli
85
What do cuboidal and columnar cells do?
Line many other tubes in the body
86
What is cilliated epithelia?
* often contain goblet cells that produce mucus
* they form the surfaces of the tubes in the gas exchange system and the oviducts
* the regular waving of the cillia from side to side moves material along the inside of the tubes
87
What does compound epithelia do?
* they are found where the surfave is continually scratched and abraded such as the skin
* the thickness of the tissue protects what lies beneath as new cells continue to grow
88
What does glandular tissue do?
Secretes substances from inside the cells
89
What is connective tissue?
* the main supporting tissue in the body
| * includes bone tissue and cartilage tissue as well as packing tissue that supports and protects some of the organs
90
What is an organ?
A structure made up of several different tissues that work effectively together to carry out a particular function
91
Give example of organs in the human body
* brain
* lungs
* heart
* liver
* stomach
* large intestine
* small intestine
92
Give an example of a plant organ
The leaf
93
What are organ systems?
When a number of organs work together to carry out large scale functions in the body
94
What organs does the digestive system include?
* stomach
* pancreas
* small and large intestine
95
What organs does the nervous system include?
* the brain
* spinal cord
* peripheral nerves
