Cell Structure for Bio PDF

A2.2 Cell structure A2.2.4-A2.2.7 A2.2.1. Cells as the basic structural unit of all living organisms NOS: Students should be aware that deductive reason can be used to generate predictions from theories. Based on cell theory, a newly discovered organism can be predicted to consist of one or m...

A2.2 Cell structure A2.2.4-A2.2.7 A2.2.1. Cells as the basic structural unit of all living organisms NOS: Students should be aware that deductive reason can be used to generate predictions from theories. Based on cell theory, a newly discovered organism can be predicted to consist of one or more cells. A2.2.4. Structures common to cells in all living organisms Typical cells have DNA as genetic material and a cytoplasm composed mainly of water, which is enclosed by a plasma membrane composed of lipids. Students should understand the reasons for these structures. Plasma Membrane the outer boundary of the cell and encloses all of its contents controls the entry and exit of substances can pump substances in, even if the concentration outside the cell is very low very effective at preventing entry of unwanted or even toxic substances allows a cell to maintain concentrations of substances that are very different from those in the surrounding environment. Plasma Membrane The permeability of the plasma membrane relies on a structure based on lipids. Occasionally the plasma membrane of a cell bursts. This is known as lysis and can be caused by excess pressure or by viruses. It can even be carried out by the cell itself (autolysis). Lysis always leads to the death of the cell; this shows that the plasma membrane is a vital structure. Cytoplasm the main component of water dissolved or suspended in this water enzymes in the cytoplasm catalyse hundreds or even DNA genes, made of DNA,contain the information needed for a cell to carry out all its functions. many genes hold the instructions for making a protein. ○ some proteins are structural so are needed for growth and repair. ○ others act as enzymes, without A2.2.5—Prokaryote cell structure Include these cell components: cell wall, plasma membrane, cytoplasm, naked DNA in a loop and 70S ribosomes. The type of prokaryotic cell structure required is that of Gram-positive eubacteria such as Bacillus and Staphylococcus. Students should appreciate that prokaryote cell structure varies. However, students are not required to know details of the variations such as the lack of cell walls in phytoplasmas and mycoplasmas. Prokaryote the first organisms to evolve on Earth and they still have the simplest cell structure mostly small in size and are found almost everywhere cytoplasm is not divided into compartments by membranes (it is one uninterrupted chamber) structurally simpler than eukaryotic cells bacteria are prokaryotic prokaryotic cells do not have a nucleus 70s thicker and stronger than the membrane protects the cell maintains the shape of the cell supports the plasma membrane to prevent it from bursting. contains peptidoglycan.  Gram-positive bacteria, retains the gram stain and show a visible violet colour upon the application of mordant (iodine) and ethanol (alcohol). Gram-positive bacteria constitute a cell wall, which is mainly composed of multiple layers of peptidoglycan that forms a rigid and thick structure. Its cell wall additionally has teichoic acids and phosphate Bacillus Staphylococcus Eukaryote compartmentalize areas are separated from the rest of the cytoplasm by single or double membranes Nucleus holds the cell’s chromosomes ○ chromosome consists of one long DNA molecule attached to proteins, except when a cell is preparing to divide and the DNA is replicated ○ DNA molecules are linear rather than circular. ○ proteins are histones, arranged in globular groups like small beads, with the DNA wound around the outside has a double membrane with pores through it Ribosomes in eukaryotic cells synthesize proteins, as in prokaryotes, are larger in size ○ causes them to sink more quickly than prokaryotic ribosomes (80s)  free floating ribosomes ○ synthesizes polypeptides used within the cell bound ribosomes ○ attached to the RER ○ synthesizes polypeptides secreted from the cell or becomes integral protein ○ made in the nucleolus Mitochondria surrounded by a double membrane inner membrane is usually folded inwards (invaginated) to increase the surface area has a fluid inside called the matrix produces ATP by aerobic respiration contains DNA Endoplasmic reticulum  Smooth endoplasmic reticulum (SER) ○ series of connected flattened membranous sacs that are continuous with the RER ○ no ribosomes are present ○ not involved in protein synthesis ○ main function is to synthesize of phospholipids and cholesterol for membrane formation and repairs  Rough endoplasmic reticulum (SER) ○ series of connected flattened membranous sacs that are continuous with the SER ○ continuous with the nuclear envelope ○ ribosomes are present ○ involved in protein synthesis and release inside of RER ○ main function is to synthesize of phospholipids and cholesterol for membrane formation and repairs Golgi Apparatus flattened membrane sacs (cisternae) modifies polypeptides into their functional state sorts, concentrates and packs proteins into vesicles depending on the contents, the vesicles are dispatched to: ○ lysosome ○ plasma ,membrane ○ secretions to the outside of the cell via exocytosis  membrane bound sacs that contain Vesicles and transport materials within cells ○ transport vesicles move molecules between locations inside the cell by budding off one organelle compartment and fusing with another secretory vesicles ○ secrete molecules from the cell via exocytosis how phospholipids are added to the cell membrane Lysosomes small spherical organelles enclosed by a single membrane contains enzymes ○ works in oxygen poor conditions ○ lower pH ○ degrade and recycle of the cell’s own organelles when they are too old or damaged ○ digests pathogens that have been engulfed by phagocytes Chloroplast adapted for photosynthesis captures light energy and uses it with water and carbon dioxide to produce glucose contains chlorophyll ○ light absorbing pigment (green) contains DNA Vacuoles enclosed by a single membrane plants have a central vacuole that occupies 30%-90% of the volume of the cell Function: ○ maintain turgor pressure against the cell wall  Cytoskeleton present in both prokaryotic and eukaryotic cells not considered as an organelle Functions: ○ maintain cell shape ○ organizes cell parts ○ enables cells to move and divide Includes ○ Microtubules ○ Actin filaments ○ Intermediate filaments Microtubules polymers of a protein called tubulin used for the intracellular transport of organelles and the separation of chromosomes during mitosis help plant cells to construct cell walls Centrioles paired cylindrical-shaped organelles present in animal cells consist of two groups of nine triple microtubules Function: ○ form an anchor point for microtubules during in the cytoplasm and for cilia and flagella ○ arrangement of the mitotic spindle during cell division Microfilaments also known as actin filament actin proteins arranged in a long, spiral chain the narrowest of the three cytoskeletons found in the cytoplasm of all eukaryotic cells help to maintain cell shape. Cilia and Flagella extensions for the cell surface which aid in cell movement. formed from modified centrioles called a basal body. A2.2.7. Processes of life in unicellular organisms Include these functions: homeostasis, metabolism, nutrition, movement, excretion, growth, response to stimuli and reproduction. A2.2.7. Processes of life in unicellular organisms Homeostasis—maintenance of a constant internal environment in an organism Metabolism—the sum of all the biochemical reactions that occur in a living organism Nutrition—supplying the nutrients required for energy, growth and repair in an organism Excretion—removal of waste products of metabolism from an organism Growth—an increase in size or number of cells Response to stimuli—perception of stimuli and carrying out appropriate actions in response Reproduction—production of offspring, either sexually or asexually.