Topic 2 - Cells as the Basis of Life Flashcards
(160 cards)
1
Q
What is cell theory?
A
Cell theory describes that:
All living organisms are composed of one or more cells.
Cells are the basic structural and functional units of life.
All cells arise from pre-existing cells.
Cells require and use energy.
Cells contain genetic information which is hereditary (passed down to subsequent generation).
2
Q
What are the characteristics of living things?
A
They:
- are complex with an organised structure
- take in energy from surroundings and use it to perform living functions
- have an internal composition that is chemically different from the external environment
- respond to stimuli
- reproduce themselves
- grow and develop
The cell is the smallest unit that fits all of these criteria (viruses do not count as they do not reproduce themselves or grow).
3
Q
How is the cell membrane composed?
A
The cell membrane is composed of a phospholipid bilayer (hydrophilic head and hydrophobic tail) with protein molecules embedded throughout. It is approximately 8 nanometers thick.
4
Q
What are the functions of the cell membrane?
A
- separates the intracellular environment from the extracellular environment, ensuring that they remain chemically different (concentration of subunits, pH and the presence of ions).
- regulates the passage of substances in and out of the cell.
- enable cells to recognise one another and certain ligands, as the polysaccharides attached to the proteins act as receptors
- enable the attachment of the cytoskeleton
5
Q
How is the cell membrane described by the fluid mosaic model?
A
The cell membrane is a fluid mosaic model composed of a phospholipid bilayer with protein molecules embedded in and through the layer at various points. The fluid is representative of the constantly moving phospholipids, whilst the mosaic describes the proteins embedded in the membrane.
6
Q
What are the characteristics of prokaryotic cells?
A
- generally smaller than eukaryotes
- can be as small as one micrometer
- relatively unspecialised
- cell is contained within a plasma membrane
- plasma membrane is usually surrounded by a cell wall
- cell wall often have short pili projecting from them, and sometimes larger flagella
- no membrane-bound organelles
- ribosomes are present
- do not have a nucleus, as DNA exists within the cytoplasm as a single, circular chromosome (and occasionally in rings called plasmids)
- all single-celled
7
Q
Are bacteria prokaryotic or eukaryotic?
A
Prokaryotic.
8
Q
What are the characteristics of eukaryotic cells?
A
- more organised and specialised internally
- larger than prokaryotes
- size generally ranges between 10-100 micrometers
- contain membrane bound organelles
- each organelle has a specific task within the cell
- contains a nucleus that stores the cell DNA
- have a cell membrane
- some also have a cell wall
9
Q
What are the common types of eukaryotes?
A
Protists, plants, animals and fungi.
10
Q
How is the nucleus structured?
A
The nucleus contains two membrane layers called the nuclear envelope. Within this nuclear envelope are many small holes lined with proteins called nuclear pores, allowing movement in and out of the nucleus.
11
Q
What is the function of the nucleus?
A
The nucleus stores the cell DNA, containing the hereditary information and instructions for functionality.
12
Q
What is chromatin and how does it it effect DNA?
A
A protein called chromatin is associated with nuclear DNA. During replication, chromatin condenses the long strands of DNA into the shorter X-shaped chromosomes.
13
Q
What is the location and function of the nucleolus?
A
The nucleolus is located within the nucleus, and the is site for ribosome production.
14
Q
How is the chloroplast structured?
A
Chloroplast contain two outer membranes, with a system of membranous flattened sacs called thylakoids inside. These thylakoids are stacked to form grana (singular - granum). The fluid surrounding the grana is called stroma.
15
Q
What is the function of the chloroplast?
A
The thylakoid membranes contain chlorophyll, the pigment required for photosynthesis. Thus, it is the site for photosynthesis.
16
Q
What are chloroplasts derived from?
A
Derived from a family of closely related plant organelles called plastids.
17
Q
How is the mitochondria structured?
A
The mitochondria contains two membranes, an outer and an inner which are highly folded into cristae. They also contain their own circular DNA, which resembles prokaryotic DNA.
18
Q
What is the function of mitochondria?
A
The mitochondria is involved in cellular respiration (use of oxygen and glucose to release energy and store it in Adenosine Triphosphate - ATP). Therefore, cells that require lots of energy contain lots of mitochondria.
19
Q
What are mitochondria derived from?
A
Evidence suggests that mitochondria were once bacteria that were incorporated into cells, hence the DNA that resembles prokaryotic DNA.
20
Q
Which organelles are present in which type of cells?
A
Nucleus - plant, animal and fungi
Nucleolus - plant, animal and fungi
Chloroplast - plant
Mitochondria - plant, animal and fungi
Vesicles - plant, animal and fungi
Vacuoles - plant, animal and fungi
Lysosome - animal
Rough Endoplasmic Reticulum - plant, animal and fungi
Smooth Endoplasmic Reticulum - plant, animal and fungi
Golgi Body - plant, animal and fungi
Ribosomes - plant, animal and fungi
Cytoskeleton - plant, animal and fungi
20
Q
How are vacuoles structured?
A
Vacuoles are fluid filled space bound by a membrane. They are part of the endomembrane system.
21
Q
What is the function of vacuoles in plant cells?
A
Vacuoles store organic compounds such as proteins and sugars that are stockpiled in storage cells (cells ready for germination). They can also be the main storage for inorganic molecules such as ions. Plants cells may also use vacuoles as storage for metabolic wastes that would endanger the cell if they remained in the cytoplasm. Vacuoles have a major involvement in growth as water is absorbed, elongating the vacuole which allows the cell to become larger.
22
Q
What is the function of vacuoles (vesicles) in animal cells?
A
Non-plant cells contain more, smaller vacuoles called vesicles. There are two types: food vacuoles (lysosomes) and contractile vacuoles. Lysosomes contain enzymes that digest macromolecules when a cell engulfs a particle (phagocytosis). Contractile vacuoles pump excess water out of the cell.
23
Q
What is the function of vacuoles in fungi?
A
Some fungi cells have large vacuoles, with a similar function to those in plant cells. These vacuoles act as storage sites but can also contain enzymes that break down compounds.
24
How is the endoplasmic reticulum structured?
The endoplasmic reticulum is a system of membranes (endomembrane system) that extends through the cytoplasm. It is a series of "passages" that are important for the transportation of materials around the cell. If ribosomes are attached, it is the rough endoplasmic reticulum. If ribosomes are not attached, it is the smooth endoplasmic reticulum.
25
What is the function of the rough endoplasmic reticulum?
The rough endoplasmic reticulum is the site for protein and membrane synthesis.
26
What is the function of the smooth endoplasmic reticulum?
The smooth endoplasmic reticulum is involved in the synthesis of lipids and the detoxification of drugs, poisons and alcohol.
27
How is the Golgi apparatus structured?
The Golgi apparatus is composed of flattened sacs and layered membranes.
28
What is the function of the Golgi apparatus?
The Golgi apparatus is involved in the packaging and secretion of proteins and carbohydrates. Cells that are specifically involved are secretion contain more Golgi bodies. Vesicles containing carbohydrates bud off from the Golgi body and move to the cell membrane where they fuse and release their contents outside the cell - exocytosis.
29
How is the cytoskeleton structured?
The cytoskeleton is a network of fibres throughout the cytoplasm. It is composed of three main filaments: microtubules, intermediate filaments, and microfilaments.
30
What is the function of the cytoskeleton?
The cytoskeleton:
- gives cells their shape
- is involved in cell movement
- holds organelles in place
- strengthens the cell
- acts like a cellular skeleton (but can be dismantled and reassembled in a new location)
- enables cells to hold specialized shapes or surfaces, mainly to increase surface area
31
How are microtubules structured and what is their specific function?
Microtubules are the thickest filament of the cytoskeleton. They are straight hollow rods that elongate by adding Tubulin molecules to its ends. It can be disassembled to be built elsewhere in the cell. They act as tracks that organelles equipped with motor molecules can move along. Microtubules are involved in the separation of chromosomes during mitosis and also compose the centrioles.
32
How are intermediate filaments structured and what is their specific function?
Intermediate filaments are the intermediate size of cytoskeleton filament. They are a diverse class of cytoskeleton elements, constructed from different subunits of the Keratin protein family. They are a more permanent fixture, that reinforce the shape and fixture of the organelles. They are also specialized for bearing tension.
33
How are microfilaments structured and what is their specific function?
Microfilaments are the smallest cytoskeleton filaments. They are solid rods made of the globular protein Actin. They are involved in intracellular movement, and also act as support in eukaryotes.
34
How are ribosomes structured?
Ribosomes are composed of a large and small subunit that together "read" mRNA.
35
What is the function of ribosomes?
Ribosomes are the site where cells assemble proteins. They do so from two different locations: free (floating around the cytoplasm) and bound (attached to the endoplasmic reticulum). Cells with a high rate of protein synthesis contain more ribosomes.
36
How do the proteins produced by ribosomes differ in response to the ribosome location?
Ribosomes are either free (floating around the cytoplasm) or bound (attached to the endoplasmic reticulum). Most proteins produced by free ribosomes function within the cytoplasm. Bound ribosomes produce proteins that are generally destined for inclusion into the membrane or packaging into organelles such as lysosomes.
37
How is energy defined?
Energy is defined as the capacity to do work.
38
Why do cells require energy?
Cellular processes such as movement, active transport, exocytosis, endocytosis, phagocytosis, and the synthesis of macromolecules all require energy. This enables the cell to grow, repair, reproduce and function normally.
39
How is energy obtained from the environment?
Energy must either be obtained in a physical or chemical form. Some cells can use sunlight as a physical form of energy, whilst others take in energy-rich compounds in the form of chemical energy. In both cases, energy is transformed so that is it useful. For example, plant cells have chloroplasts that transform light energy into chemical energy. Whereas, animals have muscles that convert chemical chemical energy into movement.
40
What is the difference between autotrophs and heterotrophs?
Autotrophs are self feeding. Most of them use sunlight as a physical energy source to store chemical energy (e.g. photosynthesis).
Heterotrophs gain their chemical energy from another source (e.g. eating to create physical energy).
41
What is photosynthesis (using an equation) and where does it occur?
Photosynthesis is the conversion of light energy to chemical energy.
6CO2 (g) + 6H20 (l) --light/chlorophyll--> C6H12O6 (aq) + 6O2 (g)
carbon dioxide + water --> glucose + oxygen
It occurs in the chloroplasts of plant cells, as chlorophyll absorbs light in the granum. Enzymes that catalyse the reaction are found in the granum and stroma.
42
How is energy transformed during respiration?
The breakdown of glucose, in the presence of oxygen, releases energy. This is because the amount of energy required to break the chemical bonds in the reactants (glucose and oxygen) is less than the energy released when the bonds in the products (carbon dioxide and water) are formed. Some of this energy is used by the cell to do work, whilst the rest is lost as heat.
43
What is ATP?
Adenosine Triphosphate (ATP) is one of the most important energy storage compounds in the cell. ATP (like RNA) has the nitrogen base Adenine bonded with a ribose sugar. This is bonded to three phosphate groups. The third bond is unstable and can be hydrolysed (broken down with water) to form Adenosine Diphosphate + Pi and energy.
44
What is the ATP cycle?
ATP can be converted to ADP + Pi through hydrolysis, and this process requires energy. ADP + Pi can be converted back to ATP, and this process releases energy.
45
How is ATP used and how is it acquired?
Cells use ATP continuously for cellular processes, but they also produce it continuously. The energy required to refuel ATP from ADP + Pi comes from cellular respiration.
46
What is aerobic respiration (using an equation) and where does it occur?
Most autotrophs and heterotrophs transform stored chemical energy into a form they can use through aerobic respiration. Aerobic respiration uses oxygen to break down glucose into carbon dioxide and water:
C6H12O6 (aq) + 6O2 (g) --> 6CO2 (g) + 6H2O (l)
glucose + oxygen --> carbon dioxide + water
Aerobic respiration occurs in the mitochondria.
47
How many ATP molecules are produced in aerobic respiration?
One molecules of glucose produces 36 ATP molecules when oxygen is used.
48
What is anaerobic respiration (using an equation) and where does it occur?
Anaerobic respiration, also known as fermentation, is an alternate pathway to aerobic respiration. This process happens in the cytoplasm of cells. In plants and yeasts, ethanol and carbon dioxide are produced (ethanol fermentation):
C6H12O6 (aq) --> 2C2H5OH (aq) + 2CO2 (g)
glucose --> ethanol + carbon dioxide
In animals, anaerobic respiration produces lactic acid (lactic acid fermentation):
C6H12O6 (aq) --> 2C3H6O3 (aq)
glucose --> lactic acid
49
How many ATPs do anaerobic pathways produce?
Both anaerobic pathways, ethanol fermentation and lactic acid fermentation, produce 2 ATP molecules per glucose.
50
What are the properties of ATP that make it ideal as the energy-carrying molecule in cells.
- small and water soluble (it is easily transported around the cell)
- renewable (ATP can be easily regenerated from ADP, Pi and the energy released from aerobic respiration)
- weak bond between the last phosphate (easily broken to release energy)
51
What are limiting factors?
A factor which limits the amount of product formed and, therefore, the rate of reaction.
52
What are the limiting factors of photosynthesis?
Limiting factors of photosynthesis include temperature, water availability, light intensity, and carbon dioxide concentration.
53
Why does aerobic and anaerobic respiration produce a different number of ATP molecules?
Harvesting energy occurs in a series of steps. Both processes begin with glycolysis, however, anaerobic respiration does not continue through the Krebs cycle. This means that the yield of energy (ATP) is lower for anaerobic respiration, as the glycolysis process only uses 2 ATPs and produces 4 - net release of 2 ATPs.
54
What are the effects of releasing energy in steps (metabolic pathway)?
- intermediate compounds can be used for other processes
- the reaction does not occur too quickly and burn up the cell
- the amount of energy stored in ATP molecules is maximised
- however, some energy is lost as heat (but it is the least possible that is lost)
- maintains optimum temperatures for cellular processes
55
What are cellular inputs and outputs?
In order to survive, cells require an input of matter (including gases, simple nutrients, and ions) and the removal of wastes.
56
What are the differences in inputs and outputs of autotrophs and heterotrophs?
Autotrophs make large, energy-rich organic compounds from small inorganic compounds. Heterotrophs need lots of inorganic compounds as well as the larger organic compounds that they cannot make. The products of metabolic pathways also differ depending on the type of respiration being undertaken.
57
Example of autotrophs forming organic compounds from inorganic compounds.
Inorganic compounds taken in by autotrophs include water and carbon dioxide, which are used to make glucose in photosynthesis. Nitrate/nitrite ions, phosphate ions and sulfate ions are absorbed by plants from the soil. These combine with the glucose to make lipids, amino acids, bases and nucleotides.
58
Why is the cell membrane important in terms of intracellular VS extracellular environment?
The cell membrane is important to ensure that the intracellular environment remains chemically different to the extracellular environment. Many subunits are present within the cell at high concentrations but not external to the cell. Acidity must also be kept within a narrow range. The presence of ions may also differ.
59
What is diffusion?
Diffusion is the movement of one substance from an area of high concentration to an area of lower concentration. The movement of substances flows with the concentration gradient.
60
How does equilibrium impact diffusion?
Diffusion will continue until equilibrium is reached. This does not mean the movement of particles stops, rather the movement of particles in one direction will balance the movement of particles in the opposite direction. Under these conditions, the next movement is zero and there is no concentration gradient.
61
Is diffusion a passive or an active process? Why?
Diffusion is a passive process because it does not require energy. Diffusion of a molecule is unaffected by concentration gradients of other molecules.
62
What is osmosis?
Osmosis is the diffusion of water from an area of low solute concentration to an area of higher solute concentration.
63
Is osmosis a passive or an active process? How does it impact a cell?
Osmosis is a passive process as it does not require energy, due to the flow being with the concentration gradient. Osmotic pressure is what helps maintain the shape of animal cells and provides support in plant cells.
64
What happens if osmotic balance is not maintained in animal cells VS plant cells?
If osmotic balance is not exactly right then the cell may swell up and burst, or alternatively shrivel. These effects are less severe in plant cells due to the cell wall. A plant cell placed in distilled water will completely swell up and become turgid, but if they lose water they become flaccid.
65
Why is the cell membrane classified as not only semi-permeable but selectively permeable?
Not all molecules are able to diffuse through the cell membrane. Cell size, charge and lipid solubility all affect the ability to traverse the plasma membrane. Proteins embedded in the membrane act as gates or carriers that allow these molecules through. Therefore, the plasma membrane is not just semi-permeable but selectively permeable.
66
What is facilitated diffusion and how does it work?
Facilitated diffusion is a method of transporting molecules that do not fit within the criteria for diffusion, due to their size, charge or lipid solubility, in or out of the cell via the cell membrane - using a transport protein that doesn't require energy from the cell to operate. Channel proteins can bind certain ions or molecules, and carry these across the membrane. Molecules such as glucose and amino acids make use of channel proteins to move with the concentration gradient.
67
Is facilitated diffusion a passive or an active process?
Facilitated diffusion is a passive process as it does not require energy due to the movement of molecules being with the concentration gradient.
68
What is active transport?
Active transport is used to move a molecule against the concentration gradient. This process requires energy and a carrier protein. There are numerous types of active transport including endocytosis (phagocytosis and pinocytosis) and exocytosis.
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What is endocytosis holistically?
During endocytosis (into the cell), the cell engulfs particles with the cell membrane that becomes a vacuole.
70
How does phagocytosis work?
In phagocytosis, the cell membrane engulfs a larger molecule - encapsulating it into a food vacuole. The food vacuole internalises into the cell where it fuses with a lysosome that breaks down the particle. Amoeba feed this way and macrophages work this way. Phagocytosis is selective, meaning cells do not engulf just any particle.
71
How does pinocytosis work?
Pinocytosis is a similar process to phagocytosis but it occurs on a smaller scale. Tiny vesicles form at the membrane, encapsulating molecules (commonly liquids) from the extracellular environment. Pinocytosis is also used to engulf large fat droplets in the small intestine. Pinocytosis may be non-selective.
72
What is exocytosis and how does it work?
Exocytosis (exit the cell) is the reverse process of endocytosis. Molecules packaged into vesicles can be removed from the cell by the vesicle fusing to the cell membrane. The contents are then expelled into the extracellular environment. Vesicles (made up of lipid 'balls') are formed from the Golgi body where they bud off and enter the cytoplasm. Cells that are involved with secretion such as salivary cells and hormone producing cells have high numbers of Golgi bodies.
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What are transport proteins?
Transport proteins are involved in transporting materials across the cell membrane.
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What are aquaporins?
Aquaporins are transport proteins that allow for water to move into, and out of, cells faster than what would occur through diffusion alone.
75
What are carrier proteins?
Carrier proteins are involved in facilitated diffusion and active transport. They transport sugars, amino acids and nucleosides (components of nucleotides). Whether the carrier protein is involved in active or passive transport is dependent on the material being transported. These differ from channels due to their selectivity.
76
What is a sodium-potassium pump and how does it work?
Ions are difficult to transport across the membrane, so pumps are often used. In a sodium-potassium pump, ions are moved against their concentration gradient across the cell membrane. This requires energy in the form of ATP, so that Na+ can be pumped out and K- can be pumped in.
77
Where are sodium-potassium pumps commonly used?
These pumps are crucial in nerve cells.
78
What are glucose-sodium transport proteins and how do they work?
Glucose-sodium transport proteins actively pump glucose into cells against the concentration gradient. This means that cells can gain higher concentrations of glucose. This process does not use ATP, the sodium ions generate a charge gradient which allows the glucose to move against the concentration gradient.
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Are glucose-sodium transport proteins passive or active?
Glucose-sodium transport proteins are technically a type of facilitated diffusion, however it requires an active process to set up.
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How do glucose transporters work?
Glucose transporters passively move glucose from a region of high concentration to a region of lower concentration.
81
What are the factors that affect the rate of exchange?
There are several factors that will affect the rate of exchange of materials between the cell and its environment:
- surface area to volume ratio (explains size of cells)
- concentration gradients (comparison between intracellular concentrations and extracellular concentrations)
- nature of exchange materials (how easily they can path through the membrane based on properties)
82
How does surface area to volume ratio impact rate of exchange?
As a cell increases in size, its surface area to volume ratio decreases. This means there is less relative surface area being exposed to the environment compared to the volume of the cell.
83
How do the infoldings in the mitochondria affect the rate of exchange for a biochemical process?
The infoldings increase the surface area to volume ratio of the organelle, thus, increasing the rate of exchange. This means there is more relative surface area being exposed, absorbing reactants for aerobic respiration and excreting waste products, compared to the volume of the organelle. This causes an increase in rate of reaction due to more space for enzymes like ATP synthase to act.
84
How do concentration gradients impact rate of exchange?
The greater the difference in concentration, the faster the movement across the cell membrane.
85
How does the nature of exchange materials impact the rate of exchange?
The properties of the particle being exchanged impact their ability to pass through the cell membrane. Small uncharged particles, such as O2 and CO2, can pass through the membrane easily via diffusion. Larger or charged particles, such as glucose or ions, may require assistance from channel proteins, carrier proteins or endo/exocytosis.
86
What is cell metabolism?
Biochemical processes that take place in the cell are referred to as a cell metabolism. This involves processes including macromolecule synthesis (mat-abolism) and macromolecule breakdown (cat-abolism).
87
What is the importance of membranes in cell metabolism?
In eukaryotes, various metabolic processes take place in specialised structures such as mitochondria, chloroplasts and rough endoplasmic reticulum. Membranes provide a larger surface area to volume ratio - specifically the infolding in the mitochondria and the thylakoids in the chloroplast - which increase the rate of exchange of materials.
88
How are enzymes involved in cell metabolism?
Enzymes and proteins involved in metabolism are embedded in membranes. Enzymes are biological catalysts. ATP synthase are present in mitochondria and they assist the reaction of ADP + Pi to form ATP. Chlorophyllase is the enzyme that catalyses glucose production, from chlorophyll in thylakoids.
89
Why does cell metabolism occur in many small steps?
- large steps produce unfavourable conditions (heat and acidity)
- small regulated steps release small quantities of energy that can be stored in ATP molecules
- many regulated steps also produce intermediate compounds that can be used as starting points for other reactions
- each regulated step is catalysed by a specific enzyme
90
How are biochemical processes influenced by the environment?
Biochemical processes are controlled by enzymes, which have optimal conditions that they operate in (pH, temperature, presence of inhibitors, concentration of reactants, and concentration of catalysts. If these are changed, the environmental conditions for the biochemical reaction are changed.
91
What is glycolysis?
Glycolysis is the breakdown of glucose in a process called cellular respiration.
92
Why is glycolysis considered a metabolic pathway?
Glycolysis occurs in a series of small steps, each catalysed by a specific enzyme. Intermediate compounds are created by these enzymes.
93
What are the ATP inputs and outputs of anaerobic glycolysis?
Glycolysis requires 2 ATP molecules and releases 4, meaning there is a net production of 2 ATPs.
94
What is an endergonic reaction?
If a chemical reaction results in products with more energy that the reactants, it is called endergonic (similar to endothermic - a drawing of energy).
95
How do chemicals interfere with biochemical processes?
Poisons are chemicals that interfere with biochemical processes (cyanide, carbon monoxide, snake venom, etc). They interfere with biochemical pathways by disabling one or more of the enzymes involved in these pathways.
96
What are three examples of chemicals interfering with protein synthesis?
TETRACYCLINE - effect on prokaryotes: inhibits tRNA binding to ribosomes
AMANITIN - effect on eukaryotes: stops mRNA synthesis
PUROMYCIN - effect on both: causes incomplete peptides to fall off the ribosomes
97
What are some benefits and harmful effects of radium?
Radium is a radioactive element that was used on watch faces and compasses so they glowed in the dark, but it was unknown at the time that radium induces cancer.
98
What are some benefits and harmful effects of thalidomide?
Thalidomide was a drug used in the 1960s to treat 'morning sickness' in pregnant women. Its use resulted in a generation of babies born with missing or stunted limbs.
99
How have chemicals effected agriculture holistically?
Chemicals and hormones used as herbicides, pesticides or to assist in plant growth had flow on effects for ecosystems.
100
How did DDT impact ecosystems?
During the 1950s, DDT was sprayed which killed the mosquitos but caused various other diseases to become prevalent. A species of caterpillar who consumed the mosquitoes were not killed. Wasps and insect-eating lizards that fed on these caterpillars died. Dogs and cats who ate the lizards then also died. Rat populations flourished as the dogs and cats no longer controlled them. These rats then transmitted other diseases to humans.
101
What are some examples of good chemicals?
The use of immunosuppressants means that people receiving organ transplants do not reject them. Hormone treatments are also used for hypothyroidism, dwarfism, contraceptives, IVF, and diabetes.
102
How should chemicals be implemented to prevent detrimental effects?
Chemical use needs to be monitored and assessed over a period of time to ensure there are no detrimental effects.
103
What happens in relation to DNA in all types of cell division?
In all cases of cell division, DNA is replicated before division. This means that the genetic information is carried from one generation to the next.
104
How do eukaryotes reproduce?
In multicellular eukaryotes, regular cells divide by mitosis whereas sex cells are produced by meiosis.
105
How do prokaryotes reproduce?
Prokaryotes reproduce via binary fission.
106
What is asexual reproduction in eukaryotes and what does it produce?
Asexual reproduction in eukaryotes is propagation of an organism without fertilisation. It produces a genetically identical copy of the parent cell.
107
What is budding?
Budding is a method of asexual reproduction done by plants. A bud is formed onto the plant that is genetically identical to the parent - a clone (except for the rare occurrence of mutations). This can then be harvested and replanted.
108
What is vegetative propagation?
Plants can also reproduce mitotically via vegetative propagation. This includes various processes like fragmentation (where a part is cut off which grows roots to become a whole new plant), sprouts from root systems (can produce whole forests), and apromixis (where a plant produces a flower that does not need fertilisation - ovule becomes a seed that is windblown for dispersal).
109
Why can plants sustain or renew growth indefinitely?
Plants have a range of undifferentiated cells meaning they can sustain or renew growth indefinitely.
110
What are the requirements of sexual reproduction in eukaryotes?
Sexual reproduction requires genetic information from two cells. In some cases this does not have to come from two different organisms (i.e. flowers self-pollinate). But in organisms that require two cells, the male and female sex cells are called gametes.
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How are gametes produced?
Gametes are produced by meiosis, which produces cells with half the number of chromosomes. Gametes unite in fertilisation, which makes a cell with the starting number of chromosomes.
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What are somatic cells and how are they produced?
The non-sex cells in an organism are called somatic cells. This means they have a full complement of chromosomes (in humans, this is 46). Somatic cells are produced by mitosis.
113
Describe the process of binary fission.
The DNA, which is present in a singular double helix ring called a nucleoid, is replicated (unzipping of segments occurs so that the code can be complementary copied). This creates a duplicated nucleoid that is identical to the first. Both nucleoids are attached to the cell membrane by proteins. As the cell elongates, the nucleoids move further apart. The cell then pinches across the equator, and the cell wall separates it into two daughter cells.
114
What is mitosis?
Mitosis is a process of asexual reproduction that occurs in eukaryotes. It produces two genetically identical daughter cells.
115
What are the stages of mitosis?
PMAT - interphase, prophase, metaphase, anaphase, and telophase/cytokinesis.
116
Describe interphase.
The normal life of a cell, which consists 90% of the cell's time, and is the phase between mitosis. Cell growth and metabolic activities are occurring within this period. The chromosomes replicate but do not condense, remaining in loosely packed chromatin. The centrioles also duplicate during interphase.
117
Describe prophase.
The chromosomes begin to condense and becomes visible as loose X shapes (sister chromatids joined by a centromere). The centrioles begin to move away from each other, retaining connection through microtubules which create the mitotic spindle. The nuclear envelope fragments and the microtubules of the mitotic spindle then invade the nucleus, connecting to the kinetochore on the centromere region.
118
Describe metaphase.
The centriole pairs are positioned at opposite ends of the cell, with the microtubules of the spindles connected to the centromere of the chromosomes - which convene on the metaphase plate of the cell.
119
Describe anaphase.
The pairs of chromatids move apart as the spindle fibres condense, pulling them towards the centrioles.
120
Describe telophase.
The polar fibres extend the cell even further, and the daughter nuclei begin to form from the fragments of the parent nuclear membrane. The cleavage furrow forms, nucleoli reappear and the chromatin fibre uncoils.
121
Describe cytokinesis.
The division of the cytoplasm occurs along the cleavage furrow, which pinches the cell in two.
122
What is the centre of a sister chromatid called?
Centromere.
123
Are gametes diploid or haploid?
Haploid as they contain half the normal chromosome number of the somatic cells.
124
What does fertilisation do?
Fertilisation restores the diploid number. Two haploid cells fuse (fertilise) to create a diploid cell.
125
How is mitosis similar to meiosis?
Meiosis undergoes similar 'phases' as mitosis, however, there are two consecutive divisions which results in half the chromosome number (haploid cells).
126
What is the purpose of meiosis?
The purpose of meiosis is to halve the chromosome number, but also to introduce genetic variability in various manners.
127
What is synapsis and when does it occur?
During prophase 1, homologous chromosome pairs get together in a process called synapsis. The two chromosome with their replicated sister chromatids are called bivalents. Each chromosome has a homologous pairing (one from the mother and one from the father, making up the 46 human chromosomes).
128
What is crossing over?
Crossing over is an event where sections of non-sister chromatids might touch, break off and then rejoin - exchanging genetic material. This occurs in prophase 1, in a place called chiasma (chiasmata plural).
129
What are the three methods in meiosis that give genetic variation?
- crossing over
- random/independent assortment
- mutation
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What is random/independent assortment?
When homologous pairs line up on the metaphase plate, they do so in no particular order and without reference to any other pair. It could cause all of one gamete's chromosomes to be on one side and the remainder on the other, or (and most likely) any number of different variations.
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During the first divide, what happens to the DNA?
During anaphase 1 and telophase/cytokinesis 1, each homologous pair is separated into a new cell. They are still in their sister chromatid pairs though.
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How many cells are produced from meiosis, and are they diploid or haploid?
4, and they are haploid.
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Why is controlling cell division important?
Uncontrollable cell division is a characteristic of cancer. However, cell division is used to replace lost cells from general living or injury.
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What are stem cells?
Stem cells are cells that have the capacity to differentiate into any type of cell.
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How is the cell cycle structured?
G1 (growth metabolism) --> S (DNA replication) --> G2 (more growth and preparation for mitosis) --> M (mitosis)
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What are checkpoints within the cell cycle?
Within the cell cycle, there are checkpoints in which the activity is halted and the cell cycle does not proceed unless a specific signal is received.
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What happens during the G1 phase of the cell cycle?
During the G1 phase, growth and metabolism occurs as the cell accumulates energy in the form of ATP, glucose and oil droplets.
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What is the checkpoint in the G1 phase and what are the characteristics to pass?
At the end of the G1 phase, restriction point M (first checkpoint) occurs in which the cell 'decides' whether to continue through the cell cycle. At this checkpoint, the cell can continue into DNA replication if it was sufficient cell size, nutrients, growth factors and no DNA damage.
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What is the checkpoint in the G2 phase and what are the general characteristics to pass?
The G2 checkpoint occurs at the end of the G2 phase, after further growth and preparation for mitosis has occurred. This is where cell size, replicated DNA and the presence of specific proteins (cyclin-dependent kinase - Cdk; Cyclin) is checked for.
140
How are proteins related to passing the G2 checkpoint?
When the two proteins combine, Cyclin-dependent kinase (Cdk) and Cyclin, they form mitosis promoting factor (MPF) complex. Therefore, an increase in Cyclin stimulates mitosis as the MPF increases. Anaphase requires a decreased presence of MPF, which occurs once the spindle fibre attachment has been checked. The concentration of Cdk remains the same throughout the cell cycle.
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What is the checkpoint in the M phase and what are the characteristics to pass?
The M checkpoint occurs before anaphase during mitosis and it checks for chromosome attachment to the spindle fibres.
142
How can physical and chemical signals impact cell division?
Physical signals, such as cells touching one another in tissue culture, can inhibit cell division. Thus, chemical signals from external sources may be required to stimulate cell division. Hormones interact with the receptors of specific cells, causing the regulation of factors which lead to cell division.
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How are the chemical signal of hormones used to stimulate cell division?
Hormones are commonly present in low concentrations so cells compete for them. If more hormones are introduced, cells will divide more quickly. Therefore, MORE HORMONE = MORE GROWTH.
144
How is cancer caused?
A change in DNA sequence may result in accelerated cell division (cancer), which is passed on to subsequent generations. There is a strong correlation between carcinogens and mutagenesis, meaning mutations often result in cancer. An accumulation of changes is often needed to initiate cancer.
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What are the potential carcinogens that can result in changed to nucleotide sequences?
- mutagenic chemicals
- ionising radiation
- viruses
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How is the cell cycle connected with cancer?
Cancer cells also appear to have abnormal cell cycles. In some cases, the checkpoints do not function and no growth factors are needed. In other cases, the cancer cells produce their own growth factors.
147
How does translocation/transposition of a gene lead to cancer?
Translocation/transposition causes a new promotor to be formed that overlaps the original, causing normal growth-stimulating proteins to become in excess - leading to cancer.
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How does gene amplification of a gene lead to cancer?
Multiple promotor regions are formed along the gene, causing normal growth-stimulating proteins to become in excess - leading to cancer.
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How does point mutation of a gene lead to cancer?
Within a control element, a point mutation forms an oncogene, causing normal growth-stimulating proteins to become in excess - leading to cancer. Within the gene, a point mutation forms an oncogene, causing hyperactive or degradation-resistant protein.
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What is cell culturing?
Cell culturing is growing the same type of cells under constant conditions.
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What are the advantages of cell culturing?
- millions of cells can be grown in a small space
- hundreds of generations can be studied in a short span of time
- this means that mutations can be detected easily and the organisms carrying them isolated
- advancements in biochemistry can be made by studying mutant cells lacking one enzyme
- individual cells can be grown to study their properties
- ethical testing of cultures is enabled
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How are animal cells cultured?
The specific tissue is minced for culturing. It is then disaggregated by use of enzymes. The cells are inoculated in a fresh culture medium. A confluent culture is created, in which the cells are separated using enzymatic disaggregation. Subculturing or passaging then occurs. The cells are then cryopreserved for further use.
153
What is an application of animal cell culturing?
Spray-on skin (healing treatment for burn wounds):
A sample of donor skin is taken. The skin cells are released by trysin digestion and scraping. A suspension made of skin cells is then sprayed onto the wound. The spray-on skin cells proliferate and bind together, forming a new layer of skin.
154
How are plant cells cultured?
A small group of cells are removed from the donor and washed with alcohol to remove contaminating microbes. These cells are placed in a nutrient medium that contains hormones and glucose. The cells can divide into roots or shoots or both depending on the hormone concentrations used. This produces hundreds of clones of a plant. Alternatively, the cell walls are dissolved and two cells are made to fuse creating hybrid species.
155
What is an application of plant cell culturing?
Metabolite production (producing many copies of something useful):
metabolite/protein produced - AAT
matrix - membrane
plant cell - oryza sativa
application - prevents emphysema, hepatitis and skin disorders
156
What are the requirements of cell culturing?
All tissue culturing requires sterile conditions to avoid unwanted growth. The culture medium must have all of the correct ingredients to promote cell growth. Water availability, pH and temperature need to be maintained consistent. The medium should be well aerated (unless growing a monolayer). For plants, light is also required.
157
What is the major disadvantage of cell culturing?
It is costly.
158
How are sterile conditions upheld in cell culturing?
All tissue culturing requires sterile conditions to avoid unwanted growth. This is usually performed in a laminar flow cabinet, which is exposed to UV light when not in use and wiped down with 70% ethanol before and after use. Lids from flasks and plates are removed for the shortest time possible, and tools are sterilised with ethylene oxide.
159
Explain how hormones regulate cell division.
Hormone is released by a signal cell and attaches to specific cell membrane receptors - that have a complementary shape to the hormone - on a target cell. Binding eventually leads to the process of transcription and translation within the cell, which produces a gene product that stimulates (or inhibits) cell division.
