1
Q
The three parts of Cell Theory
A
- the cell is the basic unit of life
- all living organisms are composed of cells
- cells come from pre-existing cells
2
Q
Who named cells?
A
Robert Hooke used the word ‘cell’ to refer to the smallest unit of life
3
Q
Who developed Cell Theory?
A
Theodor Schwann, Matthias Schleiden and Rudolph Virchow
4
Q
How did Cell Theory develop?
A
Development of cell theory was made possible thanks to advances in microscopy.
5
Q
Exemptions to Cell Theory:
A
- Striated muscle cells
- multi nucleated and large (30mm long) - Giant algae: Acetabularia
- cells must have a simple structure and be smaller (it is 0.5-10cm long) - Aseptate fungal hyphae
- have many nuclei, are very large and possess a continuous, shared cytoplasm
6
Q
Units used for measuring cells
A
1000 nm (nanometres) = 1 μm (micrometre)
1000 μm (micrometres) = 1 mm (millimetre)
7
Q
Examples of unicellular organisms
A
Bacteria, archaea, protozoa, unicellular algae and unicellular fungi
8
Q
What are the functions of life?
A
- Metabolism: living things undertake essential chemical reactions
- Growth: living things can increase or change in shape or size
- Response: every living thing responds to stimuli
- Homeostasis: living things maintain a stable internal environment
- Nutrition: living things exchange materials and gases with the environment
- Reproduction: where living things produce offspring and replicate they genes
- Excretion: living tings exhibit the removal of waste products
9
Q
Why are viruses not cells?
A
Viruses are a loop of DNA or RNA in a protein coat, they do not carry out the basic life functions such as reproduction or metabolism; only using a host cell.
10
Q
Paramecium, what are they?
A
They are a genus of unicellular protozoa. They are heterotrophs and use the cilia on their body to move. They are usually found in aquatic environments.
11
Q
Label and draw a paramecium diagram
A
https://kognity-prod.imgix.net/media/edusys_2/content_uploads/1.1.4.1.07838ace8a1cfc1a1327.png?w=750&auto=compress
12
Q
Chlamydomonas, what are they?
A
They are a genus of unicellular green algae (Chlorophyta). They have a cell wall, a chloroplast, an ‘eye’ that detects light, as well as two flagella to move. They are autotrophs.
13
Q
Label and draw a Chlamydomonas diagram
A
https://kognity-prod.imgix.net/media/edusys_2/content_uploads/1.1.4.2.372aad5af45ab60ded32.png?w=750&auto=compress
14
Q
Why can’t a cell just keep growing?
A
If they keep growing, their surface area to volume ration will be too small. If a cell’s surface area is too small compared to its volume, not enough of the necessary molecules can get in and not enough waste (including heat) can get out.
15
Q
How do cells increase surface area?
A
They increase via folds, such as in the brain and in the intestine.
16
Q
Why does the SA:Vol ratio decrease as an organism gets bigger?
A
As a cell grows, its volume is cubed, whereas the surface area is squared. Therefore, its surface area to volume ratio decreases.
17
Q
What happened when cells clumped together?
A
- Organisms grew larger because they were no longer limited by the size of one cell.
- Cells in such an organism were able to specialise through differentiation
- Multicellular organisms displayed emergent properties
18
Q
Differentiation
A
A process in which unspecialised cells develop into cells with a more distinct structure and function.
19
Q
Emergent properties
A
When the whole organism can do more things than individual cells are capable of, because of the interaction between the different parts
20
Q
Genome
A
The complete set of genes, chromosomes or genetic material present in a cell or organism.
21
Q
Cellular differentiation
A
When an unspecialised stem cell changes and carries out a specific function in the body. Cells differentiate to form different cell types due to the expression of different genes
22
Q
Why are some cells specialised?
A
Although each cell has the same genome, only certain genes are switched on in certain cells and not in others. This gives rise to the synthesis of certain proteins, which can trigger the specialised development of that specific cell and its descendants.
23
Q
Stem Cell
A
An undifferentiated cell of a multicellular organism that can form more cells of the same type indefinitely, and from which certain other kinds of cells arise by differentiation.
24
Q
What are the different types of stem cells? what do they do?
A
- Totipotent stem cells: Can differentiate into any type of cell including placental cells. Can give rise to a complete organism.
- Pluripotent stem cells: Can differentiate into all body cells, but cannot give rise to a whole organism.
- Multipotent stem cells: Can differentiate into a few closely related types of body cell.
- Unipotent stem cells: Can only differentiate into their associated cell type
25
Embryos and stem cells
Embryos are important sources of stem cells. Once an egg has been fertilised, it starts to divide and forms totipotent cells during the early stages, up until the eight-cell stage of the morula. Theoretically, each cell can still develop into a full and normal organism. These cells continue to divide and develop to form the pluripotent cells of the blastocyst from which all the specialised tissues of the developing embryo are generated
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How stem cells are used for Strargardt's disease
This disease causes partial to full blindness. Patients are given retinal cells derived from human embryonic stem cells, which are injected into the retina. They then can gain back their eyesight.
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How stem cells are used for leukemia
Leukemia, a type of cancer of the blood or bone marrow, is caused by high levels of abnormal white blood cells. Involves harvesting hematopoietic stem cells (HSCs), which are multipotent stem cells. HSCs can be taken from bone marrow, peripheral blood or umbilical cord blood. The HSCs may come from either the patient or from a suitable donor. The patient then undergoes chemotherapy and radiotherapy to get rid of the diseased white blood cells. Then they transplant HSCs back into the bone marrow, where they differentiate to form new healthy white blood cells.
28
How can stem cells be obtained?
- Specially created embryos
- Umbilical cord blood of a newborn
- An adult’s own tissues
29
Difference between prokaryotes and eukaryotes
- Eukaryotic cells have a separate membrane-enclosed nucleus, while the DNA of prokaryotes is freely floating in the cytoplasm.
- Eukaryotic cells have a complex system of membrane-bound organelles – known as compartmentalisation
- Prokaryotes do not have any membrane-bound organelles.
30
What was the first type of cell?
Prokaryotes are considered to be the earliest and most primitive type of cell, originating some 3.5 billion years ago. They include bacteria and archaea
31
Function: cell wall
Encloses the cell, protecting it and helping to maintain its shape; prevents the cell from bursting in hypotonic (dilute) media.
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Function: plasma membrane
Surrounds the cell, controlling the movement of substances in and out of the cell.
33
Function (prokaryotes): cytoplasm
Medium that fills the cell and is the site of all metabolic reactions.
34
Function: Pili
Protein filaments on the cell wall that help in cell adhesion and in transferring of DNA between two cells.
35
Function: Flagella
Much longer than pili, these are responsible for the locomotion of the organism. Their whip-like movement propels the cell along.
36
Function: 70S ribosomes
The sites of protein synthesis.
37
Function: nucleoid region
Controls all the activities of the cell, as well as the reproduction of the organism.
38
Function: Plasmids
Small circles of DNA that carry a few genes; often these genes give the cell antibiotic resistance and are used in creating genetically modified bacteria.
39
Ribosomes, eukaryotes and prokaryotes
Ribosomes in prokaryotic cells (70S) are smaller than ribosomes found in eukaryotic cells (80S). 70S and 80S refers to the sedimentation rate of RNA subunits.
40
How do prokaryotes reproduce?
Via binary fission. The chromosome is replicated semi-conservatively, beginning at the point of origin. Beginning with the point of origin, the two copies of DNA move to opposite ends of the cell, the cell elongates and then the plasma membrane grows inward and pinches off to form two separate, genetically identical cells
41
Eukaryotes and their groups
Eukaryotes represent one of the three domains (Bacteria, Archaea and Eukaryota) and include four kingdoms: Protocista, Fungi, Plantae and Animalia
42
Compartmentalisation
the formation of compartments within the cell by membrane-bound organelles
43
Advantages of compartmentalisation
- Greater efficiency of metabolism as enzymes and substrates are enclosed, and therefore much more concentrated, in the particular organelles responsible for specific functions.
- Internal conditions such as pH can be differentiated in a cell to maintain the optimal conditions for different enzymes.
- Isolation of toxic or damaging substances away from the cytoplasm, such as the storage of hydrolytic enzymes in lysosomes.
- Flexibility of changing the numbers and position of organelles within the cell based on the cell’s requirements.
44
Function (eukaryotes): cytoplasm
Fills the cell and holds all organelles. It also contains enzymes that catalyse various reactions (such as glycolysis) occurring within the cytoplasm.
45
Function: mitochondria
A site of cellular respiration in which ATP is generated.
46
Function: 80S ribosomes
The sites of protein synthesis. Free ribosomes produce proteins used inside the cell itself
47
Function: Nucleus
Controls all the activities of the cell, as well as the reproduction of unicellular organisms.
48
Function: Nucleolus
Part of the nucleus which is involved in the production of ribosomes.
49
Function: Smooth endoplasmic reticulum
Responsible for producing and storing lipids, including steroids.
50
Function: Rough endoplasmic reticulum
Transports the protein produced by the ribosomes on its surface to the Golgi apparatus. These proteins are usually for use outside of the cell.
51
Function: Golgi apparatus
Processes and packages proteins, which are ultimately released in Golgi vesicles.
52
Function: Vesicle
A small sac that transports and releases substances produced by the cell by fusing with the cell membrane.
53
Function: Lysosomes
Contain hydrolytic enzymes and play important roles in the destruction of microbes engulfed by white blood cells, as well as in the destruction of old cellular organelles.
54
Function: Centrioles
Play an important role in the process of nuclear division by helping to establish the microtubules.
55
Function: Vacuole
Helps in the osmotic balance of the cell and in the storage of substances. It may also have hydrolytic functions similar to lysosomes.
56
Function: Cell wall
Protects the cell, maintains its shape and prevents it from bursting in hypotonic media.
57
Function: chloroplast
These are double-membrane-bound organelles. They contain pigments (in this case mainly chlorophyll) and are responsible for photosynthesis.
58
How cells develop for their function
Exocrine gland cell: secretes enzymes into a duct, meaning that it has a well developed network of Rough ER and Golgi apparatus to produce and package enzymes (proteins)
Palisade mesophyll cell: the main purpose of the cell is to photosynthesise; meaning that it has a lot of chloroplasts.
59
Microscope resolution
the shortest distance between two separate points in a microscope’s field of view that can still be distinguished as distinct objects
60
Electrion vs light microscopes
- Electron microscopes have a much higher resolution (The higher the value, the lower the resolution.)
- An electron microscope can magnify very small objects in comparison to light microscopes
- Light is better to to study tissues and living cells as it allows observation of living organisms in colour
- light microscopes can be used to observe living specimens
61
Functions of life in Paramecium
Metabolism - Most metabolic reactions are catalysed by enzymes and take place in the cytoplasm
Growth - As it consumes food, the Paramecium enlarges. Once it reaches a certain size it will divide into two daughter cells.
Response - The wave action of the beating cilia helps to propel Paramecium in response to changes in the environment
Homeostasis - A constant internal environment is maintained by collecting excess water in the contractile vacuoles and then expelling it through the plasma membrane. This process is called osmoregulation
Nutrition - Paramecium is a heterotroph. It engulfs food particles in vacuoles where digestion takes place. The soluble products are then absorbed into the cytoplasm of the cell.
Reproduction - binary fission
Excretion - Digested nutrients from the food vacuoles pass into the cytoplasm, and the vacuole shrinks. When the vacuole, with its fully digested contents, reaches the Paramecium's anal pore, it ruptures, expelling its waste contents to the environment.
62
Functions of life in Chlamydomonas
Metabolism - Most metabolic reactions are catalysed by enzymes and take place in the cytoplasm.
Growth - Production of organic molecules during photosynthesis and absorption of minerals causes the organism to increase in size. Once it reaches a certain size it will divide into two daughter cells.
Response - senses light changes in its environment using its eye spot and then uses its flagella to move towards a brighter region to increase the rate of photosynthesis.
Homeostasis - A constant internal environment is maintained by collecting excess water in the contractile vacuoles and then expelling it through the plasma membrane. This process is called osmoregulation
Nutrition - Chlamydomonas is an autotroph; it uses its large chloroplast to carry out photosynthesis to produce its own food.
Reproduction - It can carry out both sexual and asexual reproduction. When Chlamydomonas reaches a certain size, each cell reproduces, either by binary fission or sexual reproduction.
Excretion - It uses the whole surface of its plasma membrane to excrete its waste products
63
What does the structure of biological membranes allow them to do?
It makes them fluid and dynamic
64
Who and when proposed the fluid mosaic model?
Singer and Nicolson in 1972
65
What does the fluid mosaic model show?
According to this model, biological membranes consist of phospholipid bilayers with proteins embedded in the bilayer, making the membrane look like a mosaic.
66
Phospholipid
A lipid where one of the fatty acids has been replaced by a phosphate group
67
Hydrophilic and hydrophobic phospholipid
The phosphate heads are hydrophilic because of their charge, while fatty acids, which are non-polar, are hydrophobic
68
Amphipathic molecule
A molecule that has both a hydrophilic and a hydrophobic part
69
How is the phospholipid bilayer formed?
The amphipathic properties of phospholipids explain the formation of the lipid bilayer: the hydrophilic phosphate heads face the watery environment (cell cytoplasm and extracellular fluid), while the hydrophobic fatty acid chains are sandwiched in between, completely isolated from the water
70
Integral and peripheral proteins
Integral proteins are amphipathic (they have hydrophobic and hydrophilic properties) and are embedded in the plasma membrane. In most cases, they pass completely through the membrane. Peripheral proteins are polar (hydrophilic) and are attached to the outside of the plasma membrane.
71
Channel proteins on the plasma membrane
Some proteins have a pore/channel that allows the passive transport (no energy required) of substances between the inside and outside of the cell.
72
Carrier proteins on the plasma membrane
These proteins bind to substances on one side of the membrane and then change shape to transport them to the other side. Carrier proteins that use energy to change shape are termed protein pumps.
73
Recognition proteins
Certain proteins help the cell in differentiating between self and non-self cells.
74
Receptor proteins
These proteins usually span the whole membrane to relay information from the inside or outside of the cell.
75
Enzymes
These are proteins that enhance the rate of reactions that happen at the membrane level.
76
Glycolipids and the plasma membrane
a phospholipid and a carbohydrate attached together. They are important in maintaining the structure of the cell membrane and in cells differentiating between self and non-self cells.
77
Cholesterol and the plasma membrane
a steroid and is only found in animal cell membranes. This is vital in helping to maintain the structure of the cell membrane
78
Draw the fluid mosaic model
https://kognity-prod.imgix.net/media/edusys_2/content_uploads/1.3.1.5.d75d1538186b2ee43b15.png
79
What does cholesterol consist of?
It is made up of a non-polar part comprising four ring structures, a hydrocarbon tail, and a polar hydroxyl group (hydrophilic). Since it has both a hydrophilic and a hydrophobic region, it is considered an amphipathic molecule. This property allows cholesterol to insert itself into cell membranes by interacting with the phospholipids (which are also amphipathic)
80
What is cholesterols role?
The presence of cholesterol in the membrane restricts the movement of phospholipids and other molecules, reducing membrane fluidity. But, at low temperatures, it also disrupts the regular packing of the hydrocarbon tails of phospholipid molecules, which prevents the solidification of the membrane. This enables the membrane to stay more fluid at lower temperatures. Additionally, it reduces membrane permeability to hydrophilic molecules and ions such as sodium and hydrogen.
81
What is the main difference between the fluid mosaic model and the Davson–Danielli model?
The Davson–Danielli model had a protein layers instead of being individually embedded
82
What are the flaws of the Davson–Danielli model?
It assumed that all membranes had identical structures, which did not explain how different types of membranes could carry out different functions.
Proteins are amphipathic, though largely non-polar (hydrophobic), which makes it improbable that they would be found in contact with the aqueous environment on either side of the membrane.
83
How did the fluid mosaic model address the issues with the Davson-Danielli model?
The fluid mosaic model suggested individually embedded proteins. This allowed the hydrophilic portions of both proteins and phospholipids to be maximally exposed to water, resulting in a stable membrane structure. At the same time, it ensured that hydrophobic portions of proteins and phospholipids were in the non-aqueous environment inside the bilayer.
84
What evidence was used to prove the fluid mosaic model?
evidence from freeze fracture techniques also confirmed that proteins are embedded in the membrane. Using these techniques, biologists delaminated membranes along the middle of the bilayer. When viewed with an electron microscope, the fracture revealed an irregular rough surface inside the phospholipid bilayer. The globular structures appearing on the fractured surface were interpreted as trans-membrane proteins (that span the whole membrane) and it was deduced that proteins penetrate into the hydrophobic interior of the membrane.
The development of the MRI machine, which uses magnetic fields to study molecules, showed that the proteins in the cell membrane could move around
85
Diffusion
the movement of particles from a region of high concentration to a region of low concentration, and is the result of the random motion of particles.
86
What affects diffusion?
Temperature, surface area, size of the particles and the different concentration gradient
87
Simple diffusion, what is it?
Simple diffusion occurs in a gas or liquid medium and only requires a concentration gradient. It occurs in both living and non-living systems.In the case of simple diffusion across membranes, if a particle is too big, it cannot pass through the phospholipid bilayer of the membrane. Similarly, charged particles are repelled by hydrophobic tails in the membrane
88
Facilitated diffusion, what is it?
It is like simple diffusion but it requires channel or carrier proteins which are specific to the molecules being transported across the plasma membrane.
89
Application of facilitated diffusion
the movement of K+ ions in neurons during the generation of an action potential. It helps in moving K+ ions out of the axons to cause repolarisation. The K+ channels involved only allow the movement of K+. They are also voltage gated, that is, they open and close with changes in electrical potential to control movement of K+ ions. This is important in the functioning of neurons.
90
Osmosis
The passive movement of water molecules from a region of lower solute concentration to a region of higher solute concentration across a partially permeable membrane.
91
Osmosis and medicine
Transplant tissues need to be kept in a saline solution for storage. It is essential that the osmolarity (a measure of the solute concentration) of the saline solution is the same as that in the cytoplasm of the cells of the tissue to prevent any osmosis (gain or loss of water) that would damage the cells.
92
Hypertonic, hypotonic and isotonic
The solution with the higher concentration of solutes is called the hypertonic solution and the solution with the lower concentration of solutes is called the hypotonic solution. Equal concentration is isotonic. Water always moves by osmosis from the hypotonic solution to the hypertonic solution
93
Too much hypertonic or hypnotic
If a solution is too hypertonic, the cell will shrink and if too hypotonic, it will burst
94
Active transport
he movement of particles across membranes, requiring energy in the form of ATP
95
Where is active transport useful?
It is useful in the roots of plants. Some minerals may not be in a high enough concentration to diffuse into the cells of roots. Active transport can overcome this problem by using energy to move those substances in.
It is also useful for the epithelial cells as glucose is actively transported into the epithelial cells lining the small intestine. This creates a high concentration of glucose inside the epithelial cells, which then allows glucose to diffuse into the blood
96
Active transport by the sodium-potassium pumps
These pumps are very important in the nervous system for the maintenance of resting potential in neurons.Basically, the concentration of sodium ions needs to be relatively higher outside the neuron than inside a neuron, while potassium ions are more concentrated inside than outside the neuron.
1. When the pump is open to the inside of the axon, three sodium ions (Na+) enter the pump and attach to their binding sites.
2. ATP donates a phosphate group to the pump.
3. The previous stage causes the protein to change shape expelling Na+ to the outside.
4. Two potassium ions (K+) from outside then enter and attach to their binding sites.
5. The binding of the K+ leads to the release of the phosphate which causes the pump to change shape again so that it is only open to the inside of the axon.
6. K+ is released inside.
7. Na+ can now enter and bind to the pump again.
97
Endocytosis
a cellular process where cells take in molecules or substances from outside of the cell by engulfing them in the cell membrane. Endocytosis can be further divided into phagocytosis or pinocytosis. Pinocytosis is the taking in of liquid substances by cells (‘cell drinking’), while phagocytosis involves the absorption of solids (‘cell eating’). An example are phagocytes
98
Exocytosis
the opposite of endocytosis and involves the ejection of waste products or useful substances (such as hormones) from the inside of the cell. It can be divided into excretion (any undigested remains of the microbe that are not useful to the cell are excreted outside the cell) and secretion (Proteins synthesised by ribosomes on rough endoplasmic reticulum are first passed to the Golgi apparatus via vesicles, where they are processed and packaged)
99
Vesicles, why they important?
Vesicles play a very important role in both exocytosis and endocytosis as they allow the movement of materials within the cell.
The rough ER will package the enzymes in a vesicle formed from the membranes of the rough ER. The vesicles carrying the enzymes will then move to the Golgi apparatus, and fuse with the Golgi apparatus membrane. The enzymes will then be modified further in the Golgi apparatus and then packed in a vesicle created using the Golgi apparatus membrane. The vesicle will then move toward the plasma membrane and undergo exocytosis and release the enzymes out of the cell.
100
Osmolarity
the concentration of a solution in terms of moles of solutes per litre of solution
101
What did Louis Pasteur (1822–1895) do?
He gave crucial evidence to support the hypothesis that cells must come from pre-existing cells. His experiment disproved the theory of spontaneous generation, which stated that life could appear from a combination of dust, air and other factors. This experiment was called Pasteur's experiment.
102
Pasteur's experiment
https://kognity-prod.imgix.net/media/edusys_2/content_uploads/1.5.1.1%20Pasteurs%20experiment%20showed%20that%20spontaneous%20generation%20of%20cells%20and%20organisms%20does%20not%20occur.87ceb8c3c2ce16a9e9b0.png?w=675&auto=compress
103
What does the Miller-Urey experiment suggest?
The first cell must have come from non-living material
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What is the Miller-Urey experiment?
Miller and Urey recreated the conditions of early Earth in a closed system by including a reducing atmosphere (low oxygen) with high radiation levels, high temperatures and electrical storms. After running the experiment for a week, some simple amino acids and complex oily hydrocarbons were found in the reaction mixture
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Miller-Urey experiment
https://kognity-prod.imgix.net/media/edusys_2/content_uploads/1.5.1.2%20Miller–Urey%20experiment.13e03ee8a1b8bc2003b8.png?w=750&auto=compress
106
What are the conditions for emergence of life?
1. Simple organic molecules, such as amino acids, fatty acids and carbohydrates, must be formed.
2. Larger organic molecules, such as phospholipids, RNA and DNA, must be assembled from simpler molecules.
3. Organisms reproduce, so replication of nucleic acids must be possible.
4. Biochemical reactions require set conditions, such as pH. Therefore, self-contained structures, such as membranes, are necessary.
107
The endosymbiotic theory
This theory supports the idea that mitochondria and chloroplasts were themselves prokaryotes that were taken in by larger prokaryotes by endocytosis. Instead of being digested and broken down, these cells remained inside the host cells. Cells that could carry out aerobic respiration and hence provide energy to their host cell (which were probably anaerobes who did not need oxygen) evolved into mitochondria. Prokaryotic cells that could convert light energy to chemical energy (probably cyanobacteria) became chloroplasts and passed on sugars produced during photosynthesis to the host cell.
108
What is the evidence for endosymbiotic theory?
Mitochondria and chloroplasts:
- Have double membranes, as expected for cells taken in by endocytosis.
- Have circular naked DNA, as in prokaryotes.
- DNA is formed as single chromosomes.
- Have 70S ribosomes, as in prokaryotes.
- Divide by binary fission like prokaryotic cells.
- Are susceptible to some antibiotics.
109
What are the three main stages of the cell cycle?
1. Interphase
2. Mitosis
3.Cytokinesis
110
Interphase, what is it?
Interphase is the most active as well as the longest phase of the cell cycle. Cells will spend most of their life within this stage undergoing common cell processes such as metabolism, endocytosis, exocytosis and using and obtaining nutrients. It encompasses three important phases of the cell cycle: G1 (Gap 1), S (synthesis), and G2 (Gap 2
111
What activities happen in the G1 phase?
In the cytoplasm:
- The cell grows and functions normally undergoing everyday processes.
- Rapid protein synthesis takes place allowing the cell to grow in size.
- Proteins required for DNA synthesis (the next phase) are made.
- Mitochondria and chloroplasts (in the case of plant cells) are replicated.
112
What activities happen in the S phase?
In the nucleus:
- The amount of DNA doubles as DNA replication takes place.
- The genetic material is duplicated but no chromosomes are formed yet.
113
What activities happen in the G2 phase?
In the cytoplasm:
- Protein synthesis occurs to produce the proteins needed for cell division, such as microtubule proteins that will make up a mitotic spindle. The cell is actively preparing for cell division
114
Mitosis
the division of the nucleus into two genetically identical daughter nuclei. It involves the separation of sister chromatids into individual chromosomes which are then distributed among the daughter nuclei.
115
Cytokinesis
Once mitosis has been completed, with the formation of two nuclei with identical sets of chromosomes, the cell enters cytokinesis. In cytokinesis, the cytoplasm of a parental cell is divided between the two daughter cells
116
Cyclins
a family of proteins that control the progression of cells through the cell cycle
117
How do cyclins function?
Cyclins bind to enzymes called cyclin-dependent kinases (CDKs) and activate them. The activated CDKs then attach phosphate groups (phosphorylation) to other proteins in the cell. The attachment of phosphate triggers the other proteins to become active and carry out tasks; in this case, specific to the phases of the cell cycle
118
Cyclin concentration
https://kognity-prod.imgix.net/media/edusys_2/content_uploads/1.6.1.2.aa4a65aedf2f5548b812.jpe
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Chromosomes and mitosis
The cell has to separate the DNA that was replicated in the S phase. In eukaryotic cells, this is done through the formation of chromosomes. Eukaryotic chromosomes consist of DNA which is tightly wound around proteins called histones. Histones are basic (alkaline) proteins that form part of nucleosomes. Many nucleosomes are coiled together in a specific pattern to form a structure called a chromosome.
120
Chromosomes, sister chromatids and chromatin
During interphase, DNA is present as chromatin. Following prophase, the phase when DNA supercoiling takes place, the DNA is visible as a pair of sister chromatids that are identical to each other connected by a centromere. After the sister chromatids are separated during anaphase, they are referred to as chromosomes.
121
Draw a chromsome
https://kognity-prod.imgix.net/media/edusys_2/content_uploads/1.6.2.3%20A%20chromosome%20consisting%20of%20two%20sister%20chromatids..a52a7246e0fa381034ab.png?w=675&auto=compress
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The four phases of mitosis
prophase, metaphase, anaphase and telophase
123
Events in prophase
1. DNA supercoils causing the chromatin to condense.
2. Nucleolus disappears.
3. Nuclear membrane disintegrates.
4. Spindle fibres (made of microtubules) start to form (and are completely formed by the end of prophase).
5. Centrioles (absent from plant cells) move to opposite poles.
124
Events in metaphase
1. Spindle fibres bind to the centromere of sister chromatids and cause their movement towards the equatorial plate.
2. Sister chromatids are aligned at the equatorial plate at the end of metaphase.
125
Events in anaphase
Sister chromatids are separated (now known as chromosomes) and pulled to opposite poles by the spindle fibres.
126
Events in telophase
1. The chromosomes have reached the poles.
2. A nuclear membrane starts to reform at each pole.
3. A nucleolus appears in each new nucleus.
4. The spindle fibres disintegrate.
5. The cell elongates in preparation for cytokinesis.
6. In some cases, the invagination of the membrane is also visible (marking the beginning of cytokinesis).
127
Describe which phase is which
https://kognity-prod.imgix.net/media/edusys_2/content_uploads/1.6.2.3.36bfba9ba015c0ae6447.png
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The mitotic index
The ratio of the number of cells in a population undergoing mitosis. The formula is:
Mitotic index = (P+M+A+T)/ total cells
129
Why is the mitotic index important?
it indicates how many cells in a tissue are dividing at a given time. In a tumour, where cell division is uncontrolled, the mitotic index is higher than in normal tissue. We can therefore use the mitotic index to predict how quickly a cancer could spread and the likely outcome in reducing cell proliferation of any treatment, such as chemotherapy.
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Cytokinesis
the division of the parental cytoplasm between the two daughter cells after mitosis
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Cytokinesis in animal cells
A ring of protein (microfilaments) located immediately beneath the plasma membrane at the equator pulls the plasma membrane inward.
The inward pull on the plasma membrane produces the characteristic cleavage furrow.z
When the cleavage furrow reaches the centre of the cells, it is pinched apart to form two daughter cells.
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Cytokensis in plant cells
In plants Golgi apparatus forms vesicles that consist of material to build a new cell wall. Vesicles merge and form the cell plate. The cell plate grows and divides into two daughter cells.
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Tumourgenesis
the formation of a tumour (or several of them), which is defined as a mass of cells that divide uncontrollably
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What are the two types of tumours
benign and malignant tumours. Cancer is caused by a malignant tumour.
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Benign tumour
usually localised, and does not spread to other parts of the body. Most benign tumors respond well to treatment.
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Malignant tumour
a cancerous growth that is often resistant to treatment. It may spread to other parts of the body and sometimes recur after it has been removed.
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How is tumour formed?
When the events of the cell cycle are disrupted because of a mutation in one of the cyclins, CDKs, or a protein associated with the cell cycle, a tumour can form.
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Example of how tumours are formed
p53 is a protein involved in the regulation of the cell cycle. A mutation in the p53 gene can lead to tumour formation. In fact, over 50% of all tumours have a mutation in the p53 gene. The cell may have lost its ability to enter G1-phase, and instead continues to divide rapidly. The mutation is passed on to the daughter cells and a clump of cells starts to form.
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Mutation
a change in an organism’s genetic code
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Mutagens
agents that cause gene mutations
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Examples of mutagens
- Chemicals that cause mutations that are referred to as carcinogens, such as asbestos or dioxin.
- High-energy radiation, such as X-rays.
- Short-wave ultraviolet light.
- Some viruses such as hepatitis B.
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Oncogene
A gene that has undergone a mutation that will contribute to the development of a tumour
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Proto-oncogenes
In their normal, non-mutated state, oncogenes are termed proto-oncogenes. These proto-oncogenes then assist in the regulation of cell division.
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Primary tumours and secondary tumours
Once abnormal cell division has started at a particular place in the body, a malignant primary tumour begins to form. If left untreated, this may follow a particular development pathway to form secondary tumours
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What happens when a tumour has metastasised?
1. Cancerous cells detach from the primary tumour.
2. Some cancerous cells gain the ability to penetrate the walls of lymph or blood vessels and so circulate around the body.
3. The circulating cancerous cells invade tissues at different locations and develop, by uncontrolled cell division, into secondary tumours.
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Metastasis
the movement of cells from a primary tumour to other parts of the body where they develop into secondary tumours.
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Smoking and cancer
Research shows that there is a strong correlation with smoking and cancer (lung cancer especially)
IB Biology
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