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Lecture 3: Anatomy of Eukaryotes and Endosymbiotic Theory

In living things, such as our body, bacteria, protozoas, fungi, there are cells. These cells are broken into either eukaryotes or prokaryotes. The organelles of these cells are important in understanding how organisms work.

EUKARYOTIC CELLS: Found in algae, protozoa, fungi, animals, and plants

Organelles are found within the cytoplasm, the following is a list of organelles and their functions:

Structure and Arrangement of Eukaryotes

  1. Flagella* – found in protozoa, algae, animals, and plants. It is located within the cytoplasmic membrane protruding out of the cytoplasmic membrane. Their basal bodies are found in the cytoplasm. The shaft contains molecules of globular protein called tubulin arranged to make a tube called microtubules. The arrangement is done in a “9 + “2 formation. In Eukaryote, it is appeared as a single or multiple flagella and is found at the pole of one cell. In eukaryotes, flagella is used to penetrate a cell into a medium (sperm) and some use flagella to pull the cell through the medium (protozoa). See Euglena sp.
  2. Cilia* – are much more numerous, shorter, and found extended from the cell surface. It also contains the “9+”2 arrangement composing of tubulin microtubules. The purpose of cilia is to propel single celled eukaryotes above te surface of the cell. The motion of cilia is rhythmic. i.e. Euglena sp.

*Note: under the microscope these guys can move fairly quickly, we can use protoslo to slow them down.

Nonmembranous Organelles

  1. Ribosomes – acquires a small and large ribosomal subunit, found on SER, contains half ribonucleic acid (RNA) and half protein (ribosomal RNA), its purpose is to make peptides which will later become proteins when it is packaged by the GA
  2. Centrioles – fund in fungal and animal cells, makes centromeres and is useful in mitosis
  3. Centromeres – important in mitosis, cytokinesis, and the development of flagella and cilia. Many eukaryotic cells lack centriols (brown algal sperm, many one celled algae, are still able to form flagella and undergo mitosis and cytokineses)
  4. Cytoskeleton – gives structure in plants and tissues. Without it, the organism is amorphous.

Membranous Organelles

Nucleus – contains the nucleolus, chromosomes, and ribosomes – some organisms have one nucleus, others are multinucleate, and some may lose their nuclei (i.e. erythrocytes can only survive for a few months). A semiliquid within the nucleus is called nucleoplasm. There, you will find one or more nucleoli, chromatin (visible chromatin is chromosomes). The nuclear envelope allows mRNA (transcription) to translocate from the nucleus to the ribosome on the rough ER to make protein
Nucleolus – contains messenger RNA (mRNA) which codes for the production of ribosomes
Smooth Endoplasmic Reticulum (SER) – lipid synthesis and transportation

Rough Endoplasmic Reticulum (RER) – contains ribosomes which produces proteins (translation) that are then placed into the lumen (central canal) of the RER and may be transported throughout the cell.

Golgi Body or Golgi Apparatus (GA)– receives, processes, and packages large sequences into proteins to be exported out of the cell (note: ribosomes make peptides – which after transferred to the GA will allow the arrangement of 3D formation of peptide bindings into a function protein) The GA contains secretory vesicles, which may fuse with the cytoplasmic membrane before ejecting its contents outside the cell via exocytosis

Mitochondria* – it is the powerhouse of the cell. Similar to the nucleus, it has two membranes, each with a phopholipid bilayer. The inner membrane is folded into cristae which gives an increase in surface area. In the cristae, ATP (adenosinetriphosphate) is made. (Breaking high energy phosphate bond of ATP releases energy). Its matrix contains 70s ribosomes and a circular molecule of DNA which is used to make some RNA molecules and mitochondrial polypeptides manufactured by mitochondrial ribosomes (nuclear DNA also synthesize mitochondrial proteins by cytoplasmic ribosomes)

Chloroplasts *- found in photosynthetic eukaryotes. Similar like mitochondria and nucleus, it has 2 phospholipid bilayer and DNA. Contains 70s ribosomes, like the mitochondria, can synthesize a few polypeptides on its own. It has pigments that absorb photons and allows the production of ATP from sugar and carbon dioxide. Thylakoids, are membranous sacs found within the chloroplast that as extensive surface area where photosynthesis occurs because thyalokoid membrane contain chlorophyl. Between the thylakoids is the inner membrane called stroma. [in prokaryotes, photosynthetic lamellae, substitute for chloroplast] A stack full of thylakoids with a thylakoid membrane is called a granum

Cell membrane – made up of phospholipid bilayer. With proteins inside of it such as glucoseprotein, glycoprotein, HDL (good) and LDL (bad) cholesterol, ligand receptors, transporter proteins, ion channels.

  • cholesterol (steroid lipids aka sterols)- used to stabilize the membrane fluidity. High temperature – sterols make the plasma membrane less fluid. Low temperature – sterols make the membrane less rigid and more fluid by preventing phospholipid packaging
  • transport materials in and out of cell via: facilitated diffusion, diffusion, osmosis, active transport
  • active transportation – endocytosis, phagocytosis, pinocytosis

Membranous sacs

Lysosomes – found in animal cells, releases lysozyme, an ezyme that breakdown foreign products entering the cell such as nutrients that entered the cell via phagocytosis (i.e. white blood cells releases enzyme to destroy phagocytized pathogens). Lysosomes may also release catabolic enzymes to damage itself due to age, damaged, or diseased.

Peroxisomes – prominent in liver and kidney of mammals, derived from the ER containing oxidase and catalase, enzymes used to degrade metabolic wastes resulting in oxygen-dependent reactions. THey also contain superoxides such as hydrogen peroxide (H2O2 ) and hydroxides (H3O+), which are released by intracellular and extracellular microbes
Vacuoles and Vesicles – terms used for membranous sacs. Large vacuoles may be seen in plant and algal cells, which stores food such as starch, lipids, and other substances. Vacuoles also acts as a pressure equalizer, it maintains hydrostatic pressure

* Note: the studies of these organelles connected to the Endosymbiotic Theory

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