Cells, Viruses and Reproduction of Living Things Flashcards
(129 cards)
1
Q
Cell theory
A
- Cells are the basic building blocks of life.
- They are the fundamental units of structure, function and organisation in living organisms.
-Cell theory is a unifying concept which links all life forms on earth together.
Structure
Function
Organisation
2
Q
TISSUES
A
Group of similar cells
Working together
To perform a particular function
3
Q
ORGANS
A
Groups of different tissues
Structured so they work together
To perform a particular function
4
Q
SYSTEMS
A
Group of different organs
Working together to carry out large scale functions
Examples include the digestive system and the nervous system
5
Q
Prokaryotic cells
A
Prokaryotic simply means before the nucleus. Prokaryotic organisms are always single celled.
6
Q
Basic properties of prokaryotic cells
A
Single celled organisms
DNA suspended freely in the cytoplasm
It does not have a nucleus
Do not have membrane bound organelles
Smaller than eukaryotic cells
7
Q
Organelles within prokaryotic cells:
NUCLEOID
A
Genetic material consists of a single strand of DNA which is often circular
The DNA is folded and coiled and the area becomes very dense with DNA
This area is known as the nucleoid
8
Q
Organelles within prokaryotic cells:
PLASMIDS
A
Smaller circles of DNA
Code for a particular aspect of the cell such as a toxin
Is able to reproduce independently of the nucleoid
Can be transferred from one bacterium to another in a form of sexual reproduction using the pilli
9
Q
Organelles within prokaryotic cells:
70S RIBOSOMES
A
Not membrane bound
Involved in protein synthesis
Made up of two smaller sub-units
Larger 50s unit and a smaller 30s unit
Smaller than the 80s ribosomes found in eukaryotic cells
10
Q
Organelles within prokaryotic cells:
CELL WALLS
A
All bacterial cells have a cell wall
Contents of the cell are usually hypertonic so water moves into the cell by osmosis
The wall prevents swelling and bursting, maintain the shape of the bacterium and it gives support and protection to the contents of the cell
All have some sort of layer of peptidoglycan
11
Q
Organelles within prokaryotic cells:
SLIME CAPSULE
A
Surrounds the cell walls and covers cell markers, making the cell hard to identify
Therefore it protects the bacterium from phagocytosis
This feature is present in all prokaryotic cells and enables the cell to more easily become pathogenic
12
Q
Bacterial cells
A
Bacterial cells can either be Gram positive or Gram negative.
Which one they are depends on the type of cell wall it has
13
Q
GRAM POSITIVE BACTERIA
A
Have a thick layer of peptidoglycan
Contain chemicals such as teichoic acid
Thick layer resists staining
Therefore leaving a purple/blue colour after staining
14
Q
GRAM NEGATIVE BACTERIA
A
Thin layer of peptidoglycan
No teichoic acid
Thin layer of peptidoglycan is easily broken down
Therefore leaving the cell red in colour after staining
15
Q
How are antibiotics be used to kill bacteria?
A
Antibiotics can be used to treat most pathogenic bacteria.
They kill these bacterial cells by targeting features specific to bacterial cells, preventing them from reproducing.
Which antibiotic is used depends upon which type of bacteria is present.
If the wrong antibiotic is prescribed the person will see no benefit.
16
Q
Procedure of gram staining
A
Firstly, crystal violet is used to stain over a heat fixed culture
After a minute,the stain is poured off and the slide is rinsed with water
Then, iodine solution is added and removed after a minute
Alcohol is then added. Liposaccharides are soluble in alcohol, whereas peptidoglycan is not, so gram negative bacteria is decolourised.
The final step of the prosecure is counterstaining with red safranin for another minute. The sample is then dried and examined
17
Q
What colour does gram positive bacteria appear?
A
Under the microscope, gram positive bacteria appears violet/purple
18
Q
What colour does gram negative bacteria appear?
A
Under the microscope, gram negative bacteria appears red
19
Q
What do antibiotics usually target?
A
Antibiotics usually target features of bacterial cells that differ from eukaryotic cells, including the bacterial cell walls and 70s ribosomes
20
Q
Explain why some antibiotics are effective against gram positive bacteria and not gram negative bacteria?
(Beta-lactam antibiotics)
A
Some antibiotics, such as beta-lactam antibiotics, inhibit the formation of the peptidoglycan layer of the cell wall.
As a result, they are effective against gram positive bacteria as they have a thick peptidoglycan layer on the surface of the cell.
However, they are less effective on gram negative bacteria, as their peptidoglycan layer is hidden and is less vital to the wall structure
21
Q
Explain why some antibiotics are effective against gram positive bacteria and not gram negative bacteria?
(Glycopeptide antibiotics)
A
Glycopeptide antibiotics are large polar molecules that cannot penetrate the outer membrane layer of gram negative bacteria.
However, they are very effective against gram positive bacteria, even the ones that have developed resistance to many other antibiotics
22
Q
Explain why some antibiotics are effective against gram negative bacteria and not gram positive bacteria?
A
Polypeptide antibiotics are rarely used because they can have serious side effects.
These are very effective against gram negative bacteria because they interact with the phospholipids of the outer membrane
They do not affect gram positive bacteria
23
Q
Explain why some antibiotics are effective against both gram negative bacteria and gram positive bacteria?
A
Most other antibiotic affect both gram positive and gram negative bacteria because they target common processes such as protein synthesis by the ribosomes.
They only target prokaryotic ribosomes, not eukaryotic ribosomes.
24
Q
Cocci
A
spherical bacteria
25
Bacilli
Rod shaped bacteria
26
Spirillla
Twisted bacteria
27
Vibrios
Comma shaped bacteria
28
Obligate aerobes
Need oxygen for respiration
29
Facultative anaerobes
Use oxygen if it is available, but can manage without it
30
Obligate anaerobes
Can only respire in the absence of oxygen - oxygen will kill them
31
In what ways can you classify bacteria?
- Grouping bacteria by the way their cell walls do or do not take up gram stains
- Grouping bacteria by their shape
- Grouping bacteria by their respiratory requirements
32
Why do antibiotics that inhibit the formation the peptidoglycan layer of the cell wall not affect human cells?
They dont affect human cells as human cells do not have a peptidoglycan wall
33
Eukaryotic cells
Eukaryotic cells have membrane bound organelles and are the foundations of multi-cellular life.
34
Organelles within eukaryotic cells:
Nucleus
Contains genetic information
Largest organelle which is roughly spherical surrounded by a double membrane called a nuclear envelope which contains openings called nuclear pores.
The outer membrane is fused to the endoplasmic reticulum.
Inside the nucleus is nearly all the cells genetic material and instructions for making proteins. It also makes mRNA.
Inside the nucleus is chromatin - which contains DNA and histones and is seen as dark patches,
35
Organelles within eukaryotic cells:
| NUCLEOULUS
Extra dense area of DNA and protein
Involved in production of ribosomes
36
Organelles within eukaryotic cells:
Ribosomes
Site of protein synthesis
80S or 70S ribosomes
Made up of two smaller sub units
Created in mitochondria
37
Organelles within eukaryotic cells:
ROUGH ENDOPLASMIC RETICULUM
Found near the Nucleas and is made up of a network of flattened sacs called Cisternae, which are continuous with the Nuclear Envelope
Lots of ribosomes on its surface
It modifies and folds proteins
38
Organelles within eukaryotic cells:
| SMOOTH ENDOPLASMIC RETICULUM
Network of fluid filled membranes but NOT attached to nucleus and has NO ribosomes
Site of lipid synthesis and storage
39
Organelles within eukaryotic cells:
Mitochondria
Mitochondria are round double membrane bound organelles responsible for Aerobic Respiration.
Produces ATP that can be used to drive the cell
Their inner membrane is folded inside to form Cristae (larger surface area), which are folded in the Matrix - the central part of a Mitochondrion.
Contains unique genetic material
Replicates independently of cell
40
Organelles within eukaryotic cells:
Centrioles – The moving mechanism
Come in pairs
Made up of a bundle of nine tubules
Used in cell division and to form microtubules
-Microtubules pull the chromosomes
41
Organelles within eukaryotic cells:
| LYSOSOMES
Special type of Golgi vesicle
Contains digestive enzymes, called lysosomal enzymes which are used to hydrolyse pathogens and old cell organelles
42
Organelles within eukaryotic cells:
Golgi apparatus
The Golgi Apparatus is a stack of membrane bound flattened sacs, and are responsible for the modification of proteins received from the ER.
These proteins are then transported in vesicles around the cell.
43
Organelles within eukaryotic cells:
| CELL WALL
Not found in animal cells
Provides strength and support for a plant cell
Can be strengthened through lignin
44
Organelles within eukaryotic cells:
| CHLOROPLASTS
Found in plant cells
Are the site of photosynthesis
Are double membrane bound
45
Organelles within eukaryotic cells:
| VACUOLE
Non-permanent in animal cell
Contains cell sap which acts as a nutrient store and maintains turgor pressure
Surrounded by the tonoplast which controls movements into and out of the vacuole
Has a single membrane
46
Magnification
Magnification is a measure of how much larger an image of an object is than the actual object itself.
47
Resolution
Resolutions is a measure of the ability to distinguish between two very close objects.
48
How to calculate magnification
Magnification can be found using the following formula:
magnification = size of image / size of object
49
Importance of staining specimens in microscopy.
The cytoplasm of cells is colourless
This means that very little can be seen
To overcome this, a stain can be used
The stain used will react with a specific chemical, allowing you to see a specific organelle
Without stains it would be impossible to see most organelles down any microscope
50
How do cells divide?
Cells divide through mitosis on a regular basis to produce two identical daughter cells which can be used for growth and repair.
51
What are the main stages of the cell cycle?
The cycle consists of three main stages:
Interphase
Mitosis
Cytokinesis
52
What does the process of the cell cycle achieve?
The process achieves three things:
Growth of the zygote into an adult
Repair and replacement of cells
Asexual reproduction
53
What does the cell cycle result in?
The cell cycle results in the formation of two new genetically identical daughter cells.
54
INTERPHASE
| G1 phase
G1 Phase -Cell grows to normal size, and organelles replicate
55
INTERPHASE
| S Phase
S Phase - the cells DNA is replicated for next cell division
56
INTERPHASE
| G2 Phase
G2 Phase - organelles and other materials needed for cell division are synthesised - before a cell divides it needs 2 of everything
57
MITOSIS
This is when the nucleus divides, the process is split into 4 stages.
58
MITOSIS:
| prophase
The chromosomes condense
Nuclear envelope disappears
Centrioles move to the poles
Nucleolus begins to break down
59
MITOSIS:
| Metaphase
Spindle fibres form and attach to the centromere
Chromatids are pulled to the centre and line up along the cell equator
60
MITOSIS:
| anaphase
Chromosomes divide at the centromere and the sister chromatids separate
The spindle fibres contracts and the sister chromatids are pulled to opposite sides of the cell
61
MITOSIS:
| Telephase
Spindle fibres break down and nuclear envelopes form around the two sets of chromosomes
The nucleoli and centrioles are also re reformed
The chromosomes begin to unravel and become less dense and harder to see
62
Cytokinesis
In animal cells, a ring of contractile fibres tighten around the centre of the cell. They continue to contract until the two cells have been separated.
In plant cells, the division of the cell occurs rather differently, with a cellulose cell wall building up from inside of the cell outwards.
In both cases the end result is the same - 2 identical daughter cells are formed
63
Why do small gaps remain in the cytoplasm?
Small gaps will remain and these are known as the plasmodesta.
They allow transport and communication between cells.
64
Mitosis contributes to:
| GROWTH
Growth is a permanent increase in the cell number, size or mass.
Measuring growth is not a straight forward process as mass varies with water intake.
To overcome this problem scientists usually compare growth using a dry mass.
However, this kills the animal so further growth cannot be measured.
65
Mitosis contributes to:
| GROWTH
Growth is a permanent increase in the cell number, size or mass.
Measuring growth is not a straight forward process as mass varies with water intake.
To overcome this problem scientists usually compare growth using a dry mass.
However, this kills the animal so further growth cannot be measured.
66
Patterns in growth:
| Continuous growth
Continuous growth occurs throughout life with most growth taking place at the beginning and continuing until maturity.
67
Patterns in growth:
| Discontinuous growth
Discontinuous growth occurs inconsistently.
For example, insects grow through a series of moults, shedding their exoskeleton.
68
ASEXUAL REPRODUCTION
This occurs when mitosis results in one parent dividing into two genetically identical clones.
69
Ways of achieving asexual reproduction
```
binary fission
sporulation
regeneration
buds
runner stems and roots
fragmentation
```
70
Meiosis
This results in 4 daughter cells which are genetically different.
It forms gametes which are haploid (n) and contain half the necessary genetic information.
71
Stages of meiosis
The first division is the same as that of meiosis except that the chromosomes do not divide at the centromere.
This results in two diploid (2n) cells.
These two cells then divide again to form four gametes which are haploid (n).
72
What does meiosis result in?
Meiosis always results in genetic variation. This variation is introduced in two ways:
Independent assortment
Crossing over (recombination)
73
Independent assortment
During anaphase, chromosome pairs are pulled randomly into each cell
This results in each cell containing a different mixture of paternal and maternal chromosome
74
Crossing over (recombination)
During prophase I, homologous pairs of chromosomes line up
Sections can break off and rejoin
This again results in changes to the genome resulting in variation
The point of each break on the chromosome is known as the chiasmata
75
SPERMATOGENESIS
The diploid primordial germ cell divides several times by mitosis to form diploid spermatogonia
The spermatogonia then grow without further division until they are big enough to be called primary spermatocytes
The spermatocytes undergo meiosis. The first meiotic division results in 2 haploid cells called secondary spermatocytes
The second meiotic division results in four haploid cells called spermatids
The spermatids then differentiate in the tubules of the testes to form spermatozoa, the active gametes capable of fertilising an ovum.
76
THE SPERM
Acrosome enzymes in the head digest the zona-pellucida (acrosome reaction)
Nucleus contains haploid chromosomes
Mitochondria stores lots of energy for movement
Tail to generate the movement
77
OOGENESIS
The diploid primordial germ cells divides several times by mitosis to form diploid oogonia.
Most of the oogonia simply degenerate but only one of these will continue to grow as all materials are invested into the egg. This large cell is known as the primary oocyte
The primary oocyte undergoes meiosis. The first meiotic division results in a secondary oocyte and a polar body
This secondary oocyte then divides through meiosis after fertilisation to form an ovum (n) and a second polar body
78
THE OVUM
The egg is large with lots of food reserves
Additional polar bodies can provide support
Zona-pellucida acts as a protective layer
Cortical granules harden the membrane preventing further sperm entry
79
Chromosome mutations
These mutations occur when part of a chromosome breaks off and becomes reattached in the wrong place.
80
Types of chromsome mutation
There are 5 different types of chromosome mutation:
Translocation - the joining of part of a chromosome to another, non-homologous chromosome.
Deletion - occurs when part of a chromosome breaks off and is lost during cell division.
Duplication - when extra copies of a gene are formed in a chromosome.
Inversion - when part of the chromosome is reversed and the reinserted.
Isochromosome - occurs when the centromere does not divide properly.
81
Describe what happens if translocation is balanced or not
If the translocations are balanced, the individual is usually healthy. However, if the translocations are unbalanced the individual may have serious health problems.
82
Non disjunction
This occurs when chromosomes fail to separate correctly resulting in cells having too many or not enough chromosomes
83
Monosomy
this is lacking a chromosome (Turner's Syndrome).
84
Polysomy
this is having an extra chromosome (Down's Syndrome)
85
Aneuploidy
Either of these situations (monosomy or polysomy) can be referred to as aneuploidy. This just means the wrong number of chromosomes.
86
Viruses
All viruses have a protein coat known as a capsid
This is made up of simple repeating units known as capsomeres
This makes virus construction quick and simple
Some viruses also have an envelope allowing them to evade recognition
87
DNA virus
Genetic material is DNA
The viral DNA acts directly as a template for new viral DNA and for the mRNA needed to induce the synthesis of viral proteins
Geometrical in shape
Examples include some bacteriophages (viruses which infect bacteria) for example, lambda phage.
88
RNA virus
More likely to mutate then DNA viruses
Some contain positive ssRNA which act directly as mRNA at the ribosomes and be translated (tobacco mosaic virus)
Some contain negative ssRNA which must be transcribed before it can acts as mRNA at the ribosomes and be translated (Ebola)
89
RNA retrovirus
Special virus with a single strand of RNA that directs the synthesis of a special enzyme called reverse transcriptase
This creates DNA molecules corresponding to the viral genome
These are incorporated into the hosts DNA which now produces the virus
The cell now acts as a vial factory producing viruses which will exit the cell through exocytosis (HIV)
90
How many routes to infection?
Once a virus enters a host cell there are two different routes to infection:
91
LYSOGENIC PATHWAY
These viruses are non-virulent
They insert their DNA into the cell as a provirus
This DNA is then incorporated into the hosts DNA
The viral genome has suppressor genes making it impossible for the material to be transcribed
The virus is latent
92
LYTIC PATHWAY
DNA is inserted
The DNA is replicated immediately to produce new viruses
These new mature viruses begin to fill the host cell
This cell eventually bursts
The new viruses are free to invade other cells and the viruses is virulent
93
when are cells turned from lysogenic state
Cells can be turned from the lysogenic state when the cell is damaged, reducing the amount of repressor protein.
This allows the viral genes to be transcribed and new mature viruses will be produced.
94
POSITIVE SSRNA VIRUS REPLICATION
The single strand of RNA is sense so can be transcribed directly at the ribosomes.
The proteins made usually include RNA polymerase.
95
NEGATIVE SSRNA VIRUS REPLICATION
The single strand of RNA is antisense so must be first transcribed using RNA replicase.
The virus will then use this RNA to make additional copies of itself.
96
RNA RETROVIRUS REPLICATION
These viruses have viral RNA as their genetic material which cannot be used as mRNA.
It is translated into DNA by the viral enzyme reverse transcriptase in the cytoplasm of the cell
This virak DNA is then incorporated into the host cells DNA.
The cells DNA will now code for new viral material and new viruses will exit the cell through exocytosis.
The cell is acting as a viral factory.
97
ANTIVIRAL TREATMENT
-Viruses are not living cells because they lack metabolism.
-A virus just acts as an infective agent using a host cell to replicate its genome and produce new viruses.
-Therefore, to stop viruses treatment must stop them during replication.
-Some antivirals achieve this by doing the following:
Target the receptors by which viruses recognise their host cells
Target the enzymes that help to translate or replicate the viral DNA or RNA
Inhibit the protease enzymes that enable new virus particles to bud from host membranes
98
METHODS OF CONTROLLING VIRAL OUTBREAKS
Rapid Identification - allows for a quicker and more effective response.
Nursing in Isolation - prevents further spread of the virus although a access to such facilities are seldom found in LIC's.
Sterilising Equipment - used needles and other equipment can quickly spread disease from person to person.
Other Methods - include wearing protective clothing and identifying points of contact.
99
Organelles in eukaryotic cells:
The cytoskeleton
3D web like structure that fills the cytoplasm
Made up of microfilaments
Made of globular protein tubulin
Gives cytoplasm structure
Keeps organelles in place
100
Organelles in eukaryotic cells:
80s Ribosomes
Only found in eukaryotic cells
Are the site of protein synthesis
Made up of two subunits; smaller subunit (40S) and large subunit (60S)
101
Factors that have to be evaluated when considering whether a drug should be fast tracked for use in an epidemic:
Severity of the disease
Availability of other treatment
Effectiveness of normal disease control
Informed consent
Freedom of choice
102
Reasons against using untested drugs
Unexpected side effects
Deciding who gets the treatment and who doesn't
People may feel like "Guinea pigs"
Patients may not have the clarity of thought to give informed consent
The drugs may be blamed for an inevitable death
103
How is the cell cycle controlled?
The cell cycle is controlled by a number of checkpoints where the cycle moves into another phase.
The control chemicals are small proteins called cyclins. These build up and attach to enzymes called cyclin dependent kinases (CDKs).
The cyclin/ CDK complex that is formed phosphorylates other proteins, changing their shape and bringing about the next stage in the cell cycle. For example condensing the chromosomes.
104
Fertilisation
This occurs when a male and female gametes fuse together to form a zygote.
This process triggers a number of mechanisms which prevent polyspermy.
105
The process of fertilisation:
| CAFC
Capacitation
The surface of the sperm cell undergoes changes that are essential to enabling the acrosome reaction and sperm entry.
Acrosome Reaction
Enzymes from the head of the sperm are released, digesting a pathway through the zona-pellucida.
Fusion of the Sperm Head
The sperm and the egg fuse resulting in a depolarisation. This acts as a fast block to further sperm entry.
Cortical Reaction
The egg releases cortical granules which harden the egg membrane. This acts as a slow more permanent block to further sperm entry.
106
Early development of the embryo to blastocyst stage
The first stage of the process is known as cleavage. Cleavage involves a special kind of mitosis, in which cells divide repeatedly without the normal interphase for growth between divisions
The result of cleavage is a mass of small, identical and undifferentiated cells forming a hollow sphere known as a blastocyst. In humans this process takes 5-6 days, occurring as the zygote is moved along the oviduct towards the uterus and as it enters the uterus
One large zygote cell forms a large number of small cells in the early embryo. Th tiny cells of the early human embryo are known as embryonic stem cells
107
Types of cells in embryo
The very earliest cells in an embryo are totipotent- totipotent cells can divide into any type of cell.
In the blastocyst, the outer layer of cells goes on to form the placenta, and the inner layer of cells have already lost some of their ability to differentiate.
They can form almost all of the cell types needed in the future but not tissue such as the placenta - we say that they are pluripotent .
108
Where are pollen grains formed?
Pollen grains are formed on the anthers - the male part of the plant.
109
How are pollen grains formed?
Each anther contains 4 pollen sacs
These sacs contain many diploid (2n) microspore mother cells
Each microspore mother cell divides twice by meiosis to form 4 haploid microspores (n)
The nucleus in each pollen grain then divides by mitosis to produce a generative nucleus and a pollen tube nucleus.
110
Where are embryo sacs formed?
Embryo sacs are found the ovule - the female part of the plant.
111
How are embryo sacs formed?
Megaspore mother cells diploid (2n) divide by meiosis to form 4 haploid megaspores (n)
One of these will then undergo three mitotic divisions to form 8 haploid nuclei
The remaining 4 haploid megaspores will degenerate
All of these nuclei remain in the embryo sac and the cytoplasm does not divide
112
The process of double fertilisation
1. Insects or the wind transfer a pollen grain from the anther of one plant to the stigma of another (pollination).
2. The pollen grain nucleus divides to form a generative nucleus and the pollen tube nucleus, both are haploid.
3. The pollen tube nucleus then produces hydrolytic enzymes, providing nutrients for the formation of the pollen tube.
4. As the generative nucleus moves down the pollen tube it divides once through mitosis.
5. The pollen tube reaches the micropyle and breaks down.
6. The two male nuclei are released into the ovule
7. One fuses with the female gamete to form a diploid zygote
8. The other fuses with the two polar bodies forming the endosprem (3n)
This process is known as double fertilisation.
113
Self-pollination
Self-pollination occurs when the pollen from the anther is deposited on the stigma of the same flower, or another flower on the same plant.
114
Cross-pollination
Cross-pollination is the transfer of pollen from the anther of one flower to the stigma of another flower on a different individual of the same species
115
Advantages of light microscope
Cheap
Easy
Colour image
116
Disadvantages of light microscopes
Much lower resolution and magnification
Cant see small organelles
117
Advantages of Scanning electron microscope
Much better magnification and resolution than light microscopes because the wavelength of electrons is shorter than the wavelength of electrons is shorter than wavelength of light
Forms a 3d image
Don't need to slice a thin section
118
Disadvantages of Scanning electron microscope
Lower magnification and resolution than transmission electron microscopes
Cant see internal structures
119
Advantages of transmission electron microscope
Better magnification and resolution than scanning electron microscope
Allows internal structures to be seen
120
Disadvantages of transmission electron microscope
Cant look at living cells
Specimens need to be in a vacuum
Need to use thin slices of specimen which can create artefacts
Does not produce colour images
121
How to use a light microscope
Start with the lowest power (magnification) objective lens
Put the slide onto the stage and hold it in place using stage clips
Use the course focus to move the stage as close to the lens as possible (without touching)
Look through the eyepiece and move focus so that the stage moves away from the lens and comes into focus
Adjust fine focus (and light intensity) for clearest image
Repeat with higher power lens if needed
122
What is a cytoskeleton?
A network of protein microfilaments and microtubules that run through the cytoplasm
123
Functions of the cytoskeleton
Provide structural support to give (animal) cells their shape
Holds organelles into position
Moves components within cells
124
Microfilaments
Protein fibres made of protein actin
Thinner than microtubules
Give cell shape (resists tension)
Anchors organelles
125
Microtubules
Hollow protein tubes
Thicker than microfilaments
Similar to centrioles
Moves organelles and resists compression
126
Name 2 things prokaryotes have that eukaryotes dont
Plasmid
Slime capsule
127
Name 2 things present in eukaryotes but not in prokaryotes
Nucleus present in eukaryotes - in prokaryotes there is no nucleus, introns or histones. They have a circular loop of DNA in the cytoplasm
Eukaryotes have membrane bound organelles such as mitochondria and Golgi apparatus
128
In what stage of the cell cycle is dna replicated?
In the S1 phase of interphase
129
How is the cell cycle controlled?
Cell cycle is controlled by a number of chemical signals made in response to different genes
This control is brought about
