A2.2 Cell Structure

• Resolution is the ability of a microscope to distinguish details of a specimen or sample.
• Advantages of the electron microscopes include Greater magnification and resolution.
• Cryogenic electron microscopy allows scientists to view proteins and other biomolecules which do not readily crystalise.
• freeze fracture electron microscopy and fluorescent stains and immunofluorescence in light Microscopy are used to study the structure of biological macromolecules.
• Cells can be classified as prokaryotic cells or eukaryotic cells.
• all cells contain the following; a phospholipid plasma membrane which controls what enters and exits the cell, a cytoplasm composed of mainly water, which is where most metabolism occurs, DNA as the genetic material and ribosomes for protein synthesis
• prokaryotic cells are smaller than eukaryotic cells and have a single circular chromosome
• prokaryotic cells structures include; a cell wall, plasma membrane, cytoplasm, 70S ribosomes, flagellum, pilus and a nucleoid region containing a naked loop of DNA
• The cell wall (composed of peptidoglycan) provides the cell with strength and support. It prevents the cell from bursting.
• Most of the metabolism that occurs in the cell occurs in the cytoplasm. It is mostly composed of water.
• The plasma membrane controls what enters and exits the cell. It is composed of phospholipids.
• The 70S ribosomes in prokaryotic cells are responsible for protein synthesis.
• The nucleoid region contains a single circular chromosome. The chromosome contains DNA (no protein) which contains the genetic information for the growth and development of the cell
• The flagellum is responsible for locomotion. Bacillus bacteria have flagella, but Staphylococcus do not.
• Pili allow bacteria to adhere to each other and other surfaces.

  Pili also allow the exchange of genetic material between bacteria.

  Bacillus bacteria have pili, but Staphylococcus do not.
• Organelles are structures with a specialized function found within cells
• Eukaryotic cells have chromosomes located in a nucleus, as well as a variety of membrane bound organelles.
• All animals, fungi and plants are eukaryotes.
• Eukaryotic cells contain; 80S ribosomes, plasma membrane, cytoplasm, nucleus, mitochondrion, cytoskeleton, RER, SER, Golgi apparatus, vacuoles, and lysosomes.
• In eukaryotes the 80S ribosomes are responsible for protein synthesis.
• Chromosomes associated with histone proteins are located in the nucleus. The nucleus has a double membrane with pores which allow mRNA to enter the cytoplasm
• Chromosomes are composed of DNA wrapped around histone proteins. The DNA is the genetic material with information for growth and development of the cell.
• the mitochondrion is a source of aerobic respiration producing ATP.
• In plants, large vacuoles are present and are involved in storing nutrients.
• in animal cells, small vacuoles are found and are involved in the removal of waste.
• Lysosomes are specialised vesicles, which contain enzymes. They are involved in the digestion of large molecules.
• The rough endoplasmic reticulum is a membrane structure with ribosomes attached. It is the site of protein synthesis, and is involved in transporting proteins to the Golgi Apparatus.
• The smooth endoplasmic reticulum is a membrane structure without ribosomes attached. It is involved in lipid synthesis, and detoxification.
• The Golgi apparatus modifies and packages proteins to be exported from the cell.
• The cytoskeleton is composed of protein microtubules, and is involved in maintaining cell shape, moving organelles, and nuclear division (mitosis and meiosis).
• the proccess of life are; homeostasis, metabolism, nutrition, movement, excretion, growth, response to stimuli, and reproduction.
• atypical cells are cells with a multinucleate or no nuclei
• Aseptate fungal hyphae (if not separated by septa) form one long multinucleate cell and Skeletal muscle cells, also known as muscle fibers, are multinucleate.
• Red blood cells, also known as erythrocytes, do not have a nucleus.

  Phloem sieve tube elements do not have a nucleus.
• the endosymbiotic theory suggests that all eukaryotes evolved from a common unicellular ancestor that had a nucleus and reproduced sexually.

  Mitochondria and chloroplasts later evolved by endosymbiosis.
• evidence for the endosymbiotic theory; the double membrane chloroplasts and mitochondria contain. 70S ribosomes (80S for eukaryotes). A singular circular chromosome with naked DNA. Reproduction through a process called binary fission.
• Stem cells are:

  ●Undifferentiated cells ●Capable of differentiating into specialized cells ●Capable of endlessly reproducing.
• Meristematic tissue in plants contains stem cells.
• Multicellularity in organisms evolved specialized tissues to carry out a range of functions, resulting in more efficient organisms, leading to longer life spans. The specialized tissue allows more efficient use of resources.