Cell biology (1.2, 1.3, 1.4, 1.5, 1.6)
Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an example of a prokaryote.
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Draw and label a diagram of the ultrastructure of a liver cell as an example of an animal cell.
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Draw and label a diagram of the ultrastructure of a palisade mesophyll cell as an example of a plant cell.
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Draw and label a diagram to show the structure of membranes.
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Identify structures in electron micrographs of E. coli.
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Identify structures in electron micrographs of palisade mesophyll cells.
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State similarities between plant and animal cells
- Both are Eukaryotic cells - DNA is stored within a nucleus - Contains larger ribosomes (80S in size) - A variety of membrane-bound organelles (e.g. mitochondria, ER, golgi apparatus)
List the functions of membrane proteins
- Hormone binding sites; - Enzymes; - Electron carriers; - Channels for (passive) transport; - Pumps for active transport; - Cell to cell recognition; - Receptors for neurotransmitters;
Identify structures in electron micrographs of liver and pancreatic exocrine gland cells.
- come back
Define mitosis
A type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth.
Explain the role of protein pumps and ATP in active transport across membranes.
Active transport is the passage of materials against a concentration gradient (from low to high). Examples of active transport include the uptake of mineral ions into root hair cells of plants. This process requires the use of protein pumps which uses the energy from ATP to translocate the molecules against the gradient. Protein pumps give cell control and transports specific substances. The hydrolysis of the ATP causes a conformational change in the protein pump resulting in the forced movement of the substance. Protein pumps are specific for a given molecule, allowing for movement to be regulated (e.g. to maintain chemical or electrical gradients) An example of an active transport mechanism is the Na+/K+ pump which is involved in the generation of nerve impulses.
Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.
After proteins have been synthesized by ribosomes they are transported to the rough endoplasmic reticulum where they can be modified. Vesicles carrying the protein then bud off the rough endoplasmic reticulum and are transported to the Golgi apparatus to be further modified. After this the vesicles carrying the protein bud off the Golgi apparatus and carry the protein to the plasma membrane. Here the vesicles fuse with the membrane expelling their content (the modified proteins) outside the cell (exocytosis). The membrane then goes back to its original state. Endocytosis is a similar process which involves the pulling of the plasma membrane inwards so that the pinching off of a vesicle from the plasma membrane occurs (made possible by membrane fluidity) and then this vesicle can carry its content anywhere in the cell.
Prokaryotic cells divide by...
Binary fission
Describe the process of binary fission
Binary fission is a form of asexual reproduction used by prokaryotic cells. In the process of binary fission: - The circular DNA is copied in response to a replication signal - The two DNA loops attach to the membrane - The membrane elongates and pinches off (cytokinesis), forming two cells
Annotate the diagram with the functions of each named structure within a palisade mesophyll cell.
Cell wall - A protective coating that protects the cell from damage or bursting, and maintains the shape of the cell. Chloroplasts - the site of photosynthesis Vacuole - plant cells have a large, fluid filled permanent vacuole, or only small temporary ones. Vacuoles store food, ions and wastes, and maintain turgor pressure in the cell.
Cells can only be formed by division of........
Cells can only be formed by division of pre-existing cells.
State that cells cannot form by spontaneous generation and instead must form from pre-existing cells by cell division
Cells cannot form by spontaneous generation and instead must form from pre-existing cells by cell division
State the functions of cholesterol in animal cell membranes (Application: Cholesterol in mammalian membranes reduces membrane fluidity and permeability to some solutes.)
Cholesterol functions to immobilise the outer surface of the membrane, reducing fluidity. It makes the membrane less permeable to very small water-soluble molecules that would otherwise freely cross. It functions to separate phospholipid tails and so prevent crystallisation of the membrane.
Cholesterol is a component of ____________ cell membranes.
Cholesterol is a component of animal cell membranes.
Chromosomes condense by _________ during mitosis.
Chromosomes condense by supercoiling during mitosis.
Prokaryotes have a simple cell structure without...
Compartmentalization
________ are involved in the control of the cell cycle
Cyclins are involved in the control of the cell cycle
Describe cytokinesis in plant and in animal cells
Cytokinesis is the process of cytoplasmic division, whereby the cell splits into two identical daughter cells. Cytokinesis occurs concurrently with the final stage of mitosis (telophase) and is different in plant and animal cells Animal Cells - After anaphase, microtubule filaments form a concentric ring around the centre of the cell - The microfilaments constrict to form a cleavage furrow, which deepens from the periphery towards the centre - When the furrow meets in the centre, the cell becomes completely pinched off and two cells are formed - Because this separation occurs from the outside and moves towards the centre, it is described as centripetal Plant Cells - After anaphase, carbohydrate-rich vesicles form in a row at the centre of the cell (equatorial plane) - The vesicles fuse together and an early cell plate begins to form within the middle of the cell - The cell plate extends outwards and fuses with the cell wall, dividing the cell into two distinct daughter cells - Because this separation originates in the centre and moves laterally, it is described as centrifugal
Cytokinesis occurs _____ mitosis and is different in plant and ______ cells.
Cytokinesis occurs after mitosis and is different in plant and animal cells.
Falsification of theories with one theory being superseded by another ‒evidence falsified the Davson-Danielli model.
Danielli and Davson proposed a model whereby two layers of protein flanked a central phospholipid bilayer. The model was described as a 'lipo-protein sandwich', as the lipid layer was sandwiched between two protein layers. The dark segments seen under electron microscope were identified (wrongly) as representing the two protein layers. There were a number of problems with the lipo-protein sandwich model proposed by Davson and Danielli: - It assumed all membranes were of a uniform thickness and would have a constant lipid-protein ratio - It assumed all membranes would have symmetrical internal and external surfaces (i.e. not bifacial) - It did not account for the permeability of certain substances (did not recognise the need for hydrophilic pores) - The temperatures at which membranes solidified did not correlate with those expected under the proposed model Falsification Evidence: - Membrane proteins were discovered to be insoluble in water (indicating hydrophobic surfaces) and varied in size - Such proteins would not be able to form a uniform and continuous layer around the outer surface of a membrane - Fluorescent antibody tagging of membrane proteins showed they were mobile and not fixed in place - Membrane proteins from two different cells were tagged with red and green fluorescent markers respectively - When the two cells were fused, the markers became mixed throughout the membrane of the fused cell - This demonstrated that the membrane proteins could move and did not form a static layer (as per Davson-Danielli) New Model: In light of these limitations, a new model was proposed by Seymour Singer and Garth Nicolson in 1972. According to this model, proteins were embedded within the lipid bilayer rather than existing as separate layers This model, known as the fluid-mosaic model, remains the model preferred by scientists today (with refinements)
Define diffusion, osmosis and active transport.
Diffusion: passive movement of particles from a region of high concentration to a region of low concentration, down a concentration gradient. Simple diffusion - Involves particles passing between the phospholipids in the membrane, movement of small or lipophilic molecules (e.g. O2, CO2, etc.) Facilitated diffusion - the passive movement of particles from a region of higher concentration to a region of lower concentration using specific protein channels, movement of large or charged molecules via membrane proteins (e.g. ions, sucrose, etc.) Osmosis - passive movement of water molecules from a region of low solute concentration to a region of high solute concentration through a partially permeable membrane, movement of water molecules (dependent on solute concentrations) Active transport involves the movement of materials against a concentration gradient (low concentration ⇒ high concentration) Because materials are moving against the gradient, it requires the expenditure of energy (e.g. ATP hydrolysis).
Explain how mitosis produces two genetically identical nuclei.
During interphase (the S phase) the DNA was replicated to produce two copies of genetic material. These two identical DNA molecules are identified as sister chromatids and are held together by a single centromere. During the events of mitosis (as described in 2.5.4), the sister chromatids are separated and drawn to opposite poles of the cell. When the cell divides (cytokinesis), the two resulting nuclei will each contain one of each chromatid pair and thus be genetically identical.
Electron microscopes have a much higher _______ than light microscopes.
Electron microscopes have a much higher resolution than light microscopes.
Compare electron and light microscopes with respect to the images they produce
Electron microscopes have two key advantages when compared to light microscopes: - They have a much higher range of magnification (can detect smaller structures) - They have a much higher resolution (can provide clearer and more detailed images) Some disadvantage of electron microscopes are that they cannot display living specimens in natural colors
Eukaryotes have a ____________ structure
Eukaryotes have a compartmentalized structure.
State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis.
Growth, embryonic development, tissue repair and asexual reproduction involve mitosis.
Describe the positions of integral proteins, peripheral proteins and glycoproteins in the cell membrane, and how their position relates to their function
Integral proteins are embedded within the phospholipids of the membrane Peripheral proteins are attached to the membrane surface Glycoproteins are proteins with short chain carbohydrate molecules attached to them on the outer surface side of the membrane (can be integral or peripheral)
Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis, and the events that occur in each.
Interphase The stage in the development of a cell between two successive divisions This phase of the cell cycle is a continuum of three distinct stages: G1 - First intermediate gap stage in which the cell grows and prepares for DNA replication S - Synthesis stage in which DNA is replicated G2 - Second intermediate gap stage in which the cell finishes growing and prepares for cell division Mitotic phase The period of the cell cycle in which the cell and contents divide to create two genetically identical daughter cells This phase is comprised of two distinct stages: Mitosis - Nuclear division, whereby DNA (as condensed chromosomes) is separated into two identical nuclei Cytokinesis - Cytoplasmic division, whereby cellular contents are segregated and the cell splits into two
Interphase is a very active phase of the ______ with many processes occurring in the _________ and _________.
Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm.
State that interphase is an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts.
Interphase is an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts.
Membrane proteins are diverse in terms of......
Membrane proteins are diverse in terms of structure, position in the membrane, and function.
Mitosis is division of the _______ into two genetically ______ daughter nuclei.
Mitosis is division of the nucleus into two genetically identical daughter nuclei.
Define mutagen, oncogenes and metastasis and describe their roles in the development of primary and secondary tumors
Mutagens A mutagen is an agent that changes the genetic material of an organism (either acts on the DNA or the replicative machinery) Mutagens may be physical, chemical or biological in origin: Physical - Sources of radiation including X-rays (ionising), ultraviolet (UV) light and radioactive decay Chemical - DNA interacting substances including reactive oxygen species (ROS) and metals (e.g. arsenic) Biological - Viruses, certain bacteria and mobile genetic elements (transposons) Mutagens that lead to the formation of cancer are further classified as carcinogens Oncogenes An oncogene is a gene that has the potential to cause cancer Most cancers are caused by mutations to two basic classes of genes - proto-oncogenes and tumour suppressor genes Proto-oncogenes code for proteins that stimulate the cell cycle and promote cell growth and proliferation Tumour suppressor genes code for proteins that repress cell cycle progression and promote apoptosis When a proto-oncogene is mutated or subjected to increased expression it becomes a cancer-causing oncogene Tumour suppressor genes are sometimes referred to as anti-oncogenes, as their normal function prevents cancer Metastasis Tumour cells may either remain in their original location (benign) or spread and invade neighbouring tissue (malignant) Metastasis is the spread of cancer from one location (primary tumour) to another, forming a secondary tumour Secondary tumours are made up of the same type of cell as the primary tumour - this affects the type of treatment required E.g. If breast cancer spread to the liver, the patient has secondary breast cancer of the liver (treat with breast cancer drugs)
Mutagens, ______ and metastasis are involved in the development of primary and secondary _______.
Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.
Annotate the diagram with the functions of each named structure in an Eukaryote
Nucleus - Contains genetic material (DNA) of the cell and controls the activity of the cell. It is surrounded by a double membrane with nuclear pores that allow for communication between the nucleus and the rest of the cell Cell membrane - Semi-permeable and selective barrier surrounding the cell that controls what substances enter and exit the cell. Also has double membrane Cytoplasm- is the site of the cell's metabolism and contains all the chemicals necessary for metabolic reactions Mitochondria - Site of aerobic respiration, which produces energy in the form of ATP for the cell Ribosomes - Site of protein synthesis (80s) Rough Endoplasmic reticulum - produces and transports the proteins that will be exported from the cell. Has ribosomes attached to surface which synthesizes proteins, which pass into the rough ER to be carried by vesicles to the needed location. Vesicles - Fluid filled sacs bound by a single membrane that are used to transport substances within as well as into/out of cells. Golgi apparatus - modifies, stores, packages and transports proteins that will be exported from the cell. Proteins are transported using vesicles Lysosomes - sacs that pick up and break down unwanted materials in the cell using enzymes that are stored within them.
Particles move across membranes by _____ diffusion, _____ diffusion, ______ and active ________.
Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.
Phospholipid molecules make up the cell membrane and are hydrophilic as well as hydrophobic. They have a hydrophilic phosphate head and two hydrophobic hydrocarbon tails. The head is made from glycerol and phosphate; while the tail made from two fatty acids. These phospholipid molecules form a bilayer. Stability to this membrane brought about by attraction between hydrophobic tails. The phospholipid bilayer forms with heads in contact with water on both sides of membrane and with hydrophobic tails found in center away from water. These phospholipids allow for membrane fluidity which helps membranes to be (functionally) stable. Phospholipids with short / unsaturated fatty acids are more fluid. These Phospholipids can move about to increase fluidity. In addition to this, in order to maintain structure the hydrophilic/hydrophobic layers restrict entry and exit of substances across the membrane.
Phospholipids form bilayer in water due to the ____________ properties of phospholipid molecules.
Phospholipids form bilayer in water due to the amphipathic properties of phospholipid molecules.
Plant cells vs Animal cells
Plants - Have plastids (e.g chloroplasts) - Have a cell wall (made of cellulose) - Have a large, central vacuole - Stores excess glucose as starch - Generally, have a fixed regular shape - Do not have centrioles - Do not have cholesterol in cell membrane Animals - Have paired centrioles within centrosome - Have cholesterol in the cell membrane - Have small temporary vacuoles (if any) - Store excess glucose as glycogen - Generally has amorphous shape - Does not have plastids - Does not have cell wall
Compare prokaryotic and eukaryotic cells.
Prokaryotes - DNA is circular - DNA is naked - Has no nucleus - Has no membrane bound organelles - 70s Ribosomes - Reproduces through binary fission - Has single chromosomes (haploid) - Small in size (1-5 micrometers) Eukaryotes - DNA bound to protein - DNA is linear - Has a nucleus - Has membrane bound organelles - 80s Ribosomes - Reproduces through mitosis and meiosis - Chromosomes are paired (diploid or more) - Larger in size (10 - 100 micrometers) REMEMBER: DORA D - DNA composition and structure O - Organelle types present and relative sizes R - Reproduction modes: differs according to chromosome structure A - Average size (exceptions may exist)
Annotate the diagram with the functions of each named structure in a prokaryote
Prokaryotic cells will typically contain the following cellular components: Cytoplasm - is the site of the cell's metabolism and contains all the chemicals necessary for metabolic reactions Nucleoid - region of the cytoplasm where the DNA is located Plasmids - autonomous circular DNA molecules that may be transferred between bacteria (horizontal gene transfer) Ribosomes - complexes of RNA and protein that are responsible for protein synthesis (70s) Cell membrane - Semi-permeable and selective barrier surrounding the cell that controls what substances enter and exit the cell. Cell wall - a protective coating that protects the cell from damage or bursting, and maintains the shape of the cell. Flagella - Long, slender projections containing a motor protein that enables movement Pili - Hair-like extensions that enable adherence to surfaces (attachment pili).
Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase).
Prophase DNA supercoils, causing chromosomes to condense and become visible under a light microscope As DNA was replicated during interphase, the chromosomes are each comprised of two genetically identical sister chromatids joined at a centromere The centrosomes move to opposite poles of the cell and spindle fibres begin to form between them (in animals, each centrosome contains 2 centrioles) The nuclear membrane is broken down and disappears Metaphase Spindle fibres from the two centrosomes attach to the centromere of each chromosome Contraction of the microtubule spindle fibres cause the chromosomes to line up separately along the centre of the cell (equatorial plane) Anaphase Continued contraction of the spindle fibres cause the two sister chromatids to separate and move to the opposite poles of the cell Once the two chromatids in a single chromosome separate, each constitutes a chromosome in its own right Telophase Once the two sets of identical chromosomes arrive at the poles, the spindle fibres dissolve and a new nuclear membrane reforms around each set of chromosomes The chromosomes decondense and are no longer visible under a light microscope The division of the cell into two daughter cells (cytokinesis) occurs concurrently with telophase
Describe the movement of particles into and out of cells under various conditions
Simple diffusion is the process by which solutes are moved along a concentration gradient in a solution or across a semipermeable membrane. Facilitated diffusion is the process of spontaneous passive transport of molecules or ions across a biological membrane via specific transmembrane integral proteins. In cellular biology, active transport is the movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient.
Define hydrophobic and hydrophilic
Substances that freely associate and readily dissolve in water are characterized as hydrophilic ('water loving'). Hydrophilic substances include all polar molecules and ions Substances that do not freely associate or dissolve in water are characterized as hydrophobic ('water-hating'). Hydrophobic substances include large, non-polar molecules (such as fats and oils)
Explain passive transport across membranes by simple diffusion and facilitated diffusion.
Substances that undergo passive transport and do not require the expenditure of energy (ATP). This can occur through simple/facilitated diffusion: Simple diffusion: - Small, non-polar (lipophilic) molecules can freely diffuse across the membrane - The plasma membrane is semi-permeable and selective in what can cross. - Substances travel from a region of high concentration to an area of lower concentration - An example of simple diffusion is the movement of gases across the membrane in animals. Oxygen and carbon dioxide dissolved in the blood is exchanged by the process of simple diffusion. Facilitated diffusion: - Polar molecules can freely diffuse across the membrane - Substances travel from a region of high concentration to an area of lower concentration - Requires proteins channels in plasma membranes - A common example of facilitated diffusion is the movement of glucose into the cell, where it is used to make ATP. Glucose although usually more concentrated outside of a cell, cannot cross the lipid bilayer via simple diffusion because it is both large and polar. To resolve this, a specialized carrier protein will transfer glucose molecules into the cell to facilitate its inward diffusion.
Outline the endosymbiotic theory
The endosymbiotic theory states that some of the organelles in today's eukaryotic cells were once prokaryotic microbes. In this theory, the first eukaryotic cell was probably an amoeba-like cell that got nutrients by phagocytosis and contained a nucleus that formed when a piece of the cytoplasmic membrane pinched off around the chromosomes. Some of these amoeba-like organisms ingested prokaryotic cells that then survived within the organism and developed a symbiotic relationship. For example: mitochondria formed when bacteria capable of aerobic respiration were ingested; chloroplasts formed when photosynthetic bacteria were ingested. They eventually lost their cell wall and much of their DNA because they were not beneficial within the host cell, so now mitochondria and chloroplasts cannot grow outside their host cell.
The first cells must have arisen from ______________.
The first cells must have arisen from non-living material.
The fluidity of membranes allows materials to be taken into cells by ______ or released by ______.
The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis.
The origin of eukaryotic cells can be explained by the __________ theory.
The origin of eukaryotic cells can be explained by the endosymbiotic theory.
Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.
The phospholipids in the cell membrane are not solid but are in a fluid state allowing the membrane to change its shape and also vesicles to fuse with it. Exocytosis uses membrane bound vesicles to transport molecules by fusing with the plasma membrane to release molecules outside the cell. Endocytosis is the mechanism whereby cells take in solids and or solutions and involves the formation of vesicles through the infolding of the cell membrane. When solids or organisms are engulfed, this is referred to as phagocytosis. The process of changing shape, breaking and reforming requires energy and is an active process.
Outline how the first cells were likely to have arisen
The theory that living cells arose from non-living matter is known as abiogenesis This process is theorised to have occurred over four key stages: There was non-living synthesis of simple organic molecules (from primordial inorganic molecules) These simple organic molecules became assembled into more complex polymers Certain polymers formed the capacity to self-replicate (enabling inheritance) These molecules became packaged into membranes with an internal chemistry different from their surroundings (protobionts)
State that tumours (cancers) are the result of uncontrolled cell division and that these can occur in any organ or tissue.
Tumours (cancers) are the result of uncontrolled cell division and that these can occur in any organ or tissue.
Vesicles move materials _____
Vesicles move materials within cells
