Topic 1 Flashcards
What does Cell Theory by Robert Hooke state?
- All living organisms are composed of cells.
- Cells are the smallest unit of life.
- Cells come from pre-existing cells and cannot be created from non-living material
Louis Pasteur and disproving spontaneous generation of cells in 1864
He first showed that micro-organisms were present in air by drawing air through a filter, then soaking the filter in alcohol to release the microbes that sank and could be collected and observed. He then took a broth, and boiled it in a swan necked flask to kill any organisms present. The condensation sealed the tube and the broth did not spoil. When the neck of the flask was broken, and air entered, the broth soon spoiled.
Unicellular Organisms
All one celled eukaryotic belong to the kingdom: Protoctista. A unicellular organism must perform all functions of life within that one cell.
Examples of Unicellular Organisms
Paramecium, Chlamydamonas, Euglena, Chlorella
Organisms which do not fit into cell theory
Aseptate Hypha of fungus, Giant Algae (Acetabularia), Striated Muscle
Cell differentiation
Different types of cells perform different functions. Each has the same DNA in the nucleus but different genes are activated, so the cells develop different structures, enzymes etc.
Emergent Propertied of cells
The properties of the whole organisms. Each cell type and tissue does it’s own job, but the organism as a whole has its own characteristic properties, made possible by the contributions of the different parts of the body.
Stem cells
Stem cells are pluripotent - cells that have not yet differentiated. Stem cells have the ability to divide repeatedly, and have the ability to become any one of a range of cell types.
Prokaryotic Cells (bacteria)
There are no membrane bound organelles within a prokaryotic cell. They divide by binary fission.
Cell wall
Made of protein. Protects the cell from the outside environment and maintains the shape of the cell. It also prevents the cell from bursting if internal pressure rises.
Plasma Membrane
Semi-permeable membrane that controls the substances moving into and out of the cell. It contains integral and peripheral proteins. Substances pass through by either active or passive transport.
Cytoplasm
Contains many enzymes used to catalyze chemical reactions of metabolism and it also contains the DNA is a region called the nucleoid. Ribosomes are also found in cytoplasm.
Pili
Help bacteria adhere to each other for the exchange of genetic materials.
Flagella
Made of protein called flagellin. Helps bacteria move around by the use of a motor protein that spins the flagellum like a propeller.
Ribosomes (70s)
They are the site of protein synthesis. Contributed to protein synthesis by translating messenger RNA.
Nucleoid
Region containing naked DNA which stores the hereditary material that controls the cell and will be passed on to the daughter cells.
Binary Fission
A method of asexual reproduction involving the splitting of the parent organism into two separate organisms, each genetically identical to the parent.
Eukaryotic Cells
Eukaryotic cells have membrane bound organelles.
Ribosomes (80s)
Found either floating free in the cytoplasm or attached to the surface of the rough endoplasmic reticulum and in mitochondria and chloroplasts. Ribosomes are the site of protein synthesis as they translate mRNA to produce proteins. Free ribosomes make the proteins used in the cell, Ribosomes on ER make proteins for export.
Rough Endoplasmic Reticulum
Can modify proteins to alter their function and/or destination. Synthesizes proteins to be excreted from the cell.
Lysosome
Contains many digestive enzymes to hydrolyse macromolecules such as proteins and lipids into their monomers.
Golgi apparatus
Received proteins from the rough endoplasmic reticulum and may further modify them. It also packages proteins before the protein is sent to its final final destination which may be intracellulaire or extra cellular.
Mitochondrion
Is responsible for aerobic respiration. Converts chemical energy into ATP using oxygen.
Nucleus
Contains the chromosomes and therefore the hereditary material. It is responsible for controlling the cell.
Compare prokaryotic and eukaryotic cells
- Prokaryotes have naked DNA which is found in the cytoplasm in a region named the nucleoid. Eukaryotes have chromosomes made up of DNA and protein which are found in the nucleus enclosed in a nuclear envelope.
- Prokaryotes do not have any mitochondria whereas eukaryotes do.
- Prokaryotes have small ribosomes (70s) compared to eukaryotes which have large ribosomes (80s).
Differences between plant and animal cells
- Animal cells only have a plasma membrane and no cell wall. Whereas plant cells have both.
- Animal cells do not have chloroplasts whereas plant cells do for the process of photosynthesis.
- Animal cells store glycogen as their carbohydrate resource whereas plants store starch.
- Animal cells do not usually contain any vacuoles and if present they are small or temporary. Plants have a large vacuole that is always present.
- Animal cells can change shape due to the lack of a cell wall and are usually rounded whereas plant cells have a fixed shape kept by the presence of the cell wall.
The phospholipid bilayer
Phospholipid molecules have a hydrophilic phosphate head and two hydrophobic hydrocarbon tails. Cell membranes are made up of a double layer of these phospholipid molecules.
Hydrophilic
Attracted to water
Hydrophobic
Not attracted to water
Membrane Proteins
Diverse in structure and function. They can be integral and may have a channel through the center or peripheral. They may be joined with carbohydrate chains to form glycoproteins.
What are membrane proteins used for?
They can act as hormone binding sites, electron carriers, pumps for active transport, channels for passive transport and also enzymes. They can be used for cell to cell communication as well as cell adhesion and cell recognition.
Cholesterol
Is an amphipathic molecule in the cell membrane meaning it contains a hydrophilic and a hydrophobic portion. Because of the way it is shaped it helps to slightly immobilize the outer surface of the membrane and make it less soluble to very small water-soluble molecules that could otherwise pass through more easily.
What does cholesterol do?
Cholesterol keeps cell membranes from being too fluid, not firm enough and too permeable. It helps maintain its fluidity. It helps separate the phospholipids at high concentrations so that the fatty acid chains can’t come together and crystallize. It helps to support membrane proteins so that they can carry out all their functions.
The Davson - Danielli model of membrane structure (DDR Model)
Accepted standard model for membrane structure from 1930 until 1972. It was a bilayer of lipids between two layers of unfolded protein. Each protein layer faced a watery environment.
Problems with the DDR Model
- When cells were rapidly frozen and then shattered before viewing, large lumps were seen within the phospholipid bilayer, not a smooth cross section as indicated by DDR.
- Membrane proteins could not be positioned to prevent contact between the polar head groups of membrane lipids and aqueous cytoplasm.
Passive Transport
Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration.
Simple Diffusion
Involves the diffusion of molecules through the phospholipid bilayer.
Facilitated Diffusion
Involves the use of channel proteins embedded in the membrane.
Osmosis
the movement of water molecules through a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration.
Active Transport
Involves the movement of substances through the membrane using energy from ATP.
Vesicles
A “packet” of membrane similar in structure to the plasma membrane.
Exocytosis
A vesicle inside a cell merging with the outer plasma membrane to release its contents.
Endocytosis
Involves the pulling of the plasma membrane inwards and the pinching off of a vesicle inside the cell.
Osmolarity
A measure of solute concentration.
Hypotonic
Having a lower osmotic pressure than another
Hypertonic
having a greater osmotic pressure than another
Isotonic
having the same osmotic pressure
The Cell Cycle - Interphase
It is the first stage of cell division and is divided into 3 phases; G1, S and G2.
The cell cycle starts with G1 during which the cell grows larger. Organelle synthesis is happening, which also leads to protein synthesis as the cell requires structural proteins and enzymes.
This is followed by S, during which the genome is replicated.
G2 is the second growth phase which marks the end of interphase. More cell growth takes place and some of the organelles divide.
Cycling
Proteins within a cell, named such bc they undergo a constant cycle of synthesis and degradation during cell division. When they are synthesized, they act as an activating protein and bind to Cdk (an enzyme) causing it to add phosphates to other proteins. The build-up of phosphates acts as a signal to the cell to move on to the next phase. Eventually, the cyclin degrades, deactivating the Cdk, and signaling the exit from a particular phase. There are two classes of cyclins: mitotic and G1 cyclins. The change of concentration of cyclin molecules is what controls the phases.
Mitosis
Normal cell division where one diploid parent cell divides to form two diploid daughter cells. Each having an identical set of pairs of chromosomes.
Mitosis - Prophase
Spindle microtubules grow and extend from each pole to the equator. Also, chromosomes super coil and become short and bulky and the nuclear envelope breaks down. Sister chromatids become visible as the end result of super-coiling of the DNA. around histone proteins (called nucleosomes). The sister chromatids (replicated DNA strands) are attached to each other at a centromere.
Mitosis - Metaphase
The chromatids move to the equator and the spindle microtubules from each pole attach to each centromere on opposite sides.
Mitosis - Anaphase
the spindle microtubules pull the sister chromatids apart splitting the centromeres. This splits the sister chromatids into chromosomes. Each identical chromosome is pulled to opposite poles.
Mitosis - Telophase
the spindle microtubules break down and the chromosomes uncoil and so are no longer individually visible. Also, the nuclear membrane reforms. The cell then divided by cytokinesis to form two daughter cells with identical genetic nuclei.
Cytokinesis
The cell dividing in two. This is the last stage during which the cytoplasm divided to create two daughter cells. In animal cells the cell is pinched in two while cells form a plate between the dividing cells.
How do you calculate the mitotic index?
number of cells with visible chromosomes / total number of cells visible
Cancer
characterized by the uncontrolled division of cells leading to tumor formation.
Mutagens
a physical or chemical agent that changes the genetic material of an organism and thus increases the frequency of mutations above the natural background level.
Proto-oncogenes
A group of genes that cause normal cells to become cancerous when they are mutated. They code for proteins that stimulate cell division, inhibit cell differentiation, and halt cell death. Oncogenes are a major molecular target for anti-cancer drug design.
Metastasis
The movement or spreading of cancer cells from one organ or tissue to another.
