Cell Parts Summary

1. Cell Parts Summary

2. Prokaryotic Cell Pili Nucleoid Ribosomes Plasma membrane Cell wall Bacterial chromosome Capsule 0.5 µm Flagella A typical rod-shaped bacterium A thin section through the bacterium Bacillus coagulans (TEM)

3. Structures External to the Cell Wall • Glycocalyx-Means sugar coat and is composed of polysaccharides, polypeptides or both that is viscous (think molasses) • A loose, unorganized glycocalyx is referred to as a slime layer • A glycocalyx that is organized and firmly attached to the cell wall is a capsule, which can often protect bacteria from host immune response cells. This may allow a microbe to be more pathogenic.

4. Flagella • Some prokaryotes have flagella (flagellum for single) • Made of proteins that for a semi-rigid helical structure that rotates clockwise or counter-clockwise • Allows for cell motility • Spirochetes use axial filaments (endoflagella) that is similar to flagella structure. Movement is corkscrew-like.

5. Pili • Consists of a protein called Pilin that are hairlike, shorter, straighter and thinner than flagella • Used for attachment rather than motility • Fimbriae and pili are often used interchangeably, but can be distinguished based on function (fimbriae for attachment, and pili for joining bacteria cells for DNA transfer.

6. Cell Wall • Complex, semi-rigid structure responsible for the shape of the cell • Surrounds the plasma membrane and protects the interior of the cell from harsh changes in the environment. (also as water pressure inside the cell increases to prevent rupturing/lysis) • Cell wall composition can be used to help differentiate bacteria, as well as provide an antibiotic target, since cell walls can contribute to pathogenicity

7. The Plasma (Cytoplasmic) Membrane • Thin structure enclosing the cytoplasm • Consists primarily of phospholipids and proteins that allow for selective permeability • Prokaryotic plasma membranes are less rigid than Eukaryotic because they lack sterols (like cholesterol), except for the Mycobacterium (Mycoplasma) which has no cell wall, but has membrane sterols.

8. Cytoplasm • The thick substance inside the plasma membrane • Consists of about 80% water and is full of proteins(enzymes) • Major structures in the cytoplasm of prokaryotes are the nucleoid region containing the DNA (and plasmids), ribosomes, and inclusion bodies

9. Nuclear area (Nucleoid) • Usually contains a single, long, continuous, and often circular chromosome • Chromosome is not surrounded by a nuclear membrane but is attached in some places to the plasma membrane • Plamids are small circular pieces of double stranded DNA that often contain genes that may help the bacteria survive harsh conditons, such as antibiotics or toxic metals

10. Ribosomes • Site of protein synthesis • Composed of two subunits of protein and rRNA (30s and 50s combine to make 70s)

11. Inclusion Bodies • Cells may accumulate and store certain nutrients • It is thought that by keeping these molecules in the inclusions the cell prevents osmotic pressure issues • Inclusion bodies can be identified according to the type of molecule is stored, some bacteria have special types that can be used for identification

12. Endospore • Gram positive cells have the ability to form a protein “shield” internally to the cell membrane • Allow bacteria to survive harsh environments • Endospores can remain dormant for thousands of years, but can resume metabolism and reproduction as a vegetative cell once it is in a nutrient rich environment

13. Eukaryotic Cell ENDOPLASMIC RETICULUM (ER) Nuclear envelope Flagellum Rough ER Smooth ER NUCLEUS Nucleolus Chromatin Centrosome Plasma membrane CYTOSKELETON Microfilaments Intermediate filaments Microtubules Ribosomes: Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm)

14. Flagella and Cilia • Used for cellular locomotion (movement) • Contain cytoplasm and are covered in a membrane or sheath (prokaryotic flagella are not) • Undulate in a wavelike motion (not rotation) • If the cell only has a few, they are often long-flagella • If they have many and short-cilia (cilium is singular)

15. Cell Wall and Glycocalyx • Most eukaryotic cells have cell walls • Cell wall difference help differentiate (ex algae have cellulose, and fungi have chitin as main components) • Protozoa do not have a typical cell wall –Pellicle • Other eukaryotic cells, like animal cells, that do not have a cell wall, protect the plasma membrane with a glycocalyx

16. The Plasma (Cytoplasmic) Membrane • Very similar to prokaryotic cells in function and basic structure • Eukaryotic membranes also contain carbohydrates and sterols • Also selectively permeable, but eukaryotic cells can use endocytosis to bring molecules inside the cell

17. Cytoplasm • Inside the plasma membrane, but external to the nucleus • Cytosol refers to the fluid portion • Contains the cytoskeleton that provides shape, structure, as well as, transportation routes inside the cell • Contains organelles where many important cellular enzymes are partitioned

18. Ribosomes • Site of protein synthesis (like prokaryotes) • Eukaryotic ribosomes are larger and denser (40s and 60s subunits that together form the 80s complex) • Mitochondria and Chloroplasts contain 70s ribosomes (Endosymbiant theory)

19. Organelles • Unlike prokaryotes, eukaryotes contain membrane bound organelles that have specific shapes and functions within the cell • Not all organelles are found in all eukaryotic cells • Organelle presence, number and distribution may depend on cell activity, age or cell specialization.

20. Nucleus • Contains most of the eukaryotic genetic information • Nuclear envelope surrounds DNA wrapped around histone proteins. • Condensed regions of chromosomes, called nucleoli, where rRNA is being synthesized • Transport across nuclear membrane through nuclear pores

21. Endoplasmic Reticulum • Continuous with the nuclear envelope • Rough ER is “studded” with ribosomes primarily producing secretory proteins and membrane molecules (like phospholipids) • Smooth ER does not have ribosomes on the outer surface, but does synthesize phospholipids, and also fats and steroids

22. Golgi Complex • First step of the transport pathway • Looks like a stack of pita bread • Proteins get modified and move via transfer vesicles • Some leave the golgi as secretory vesicles • Some leave as storage vesicles • Major storage vesicle is a lysosome

23. Lysosome • Single membrane formed from golgi complexes. • Contain digestive enzymes for breaking down molecules.

24. Vacuole • Space or cavity in the cell enclosed by a membrane • Plant vacuoles can occupy a very large percentage of space • Formed from Golgi, vacuoles have diverse functions depending on cell type, such as storage nutrients or wastes, endocytosis of food, and water storage.

25. Mitochondria • Doublemembrane bound organelle • Outer membrane is smooth, while inner membrane form folds, cristae that surround the matrix • Power house of the cell-major site of ATP production • Contain 70s ribosomes, some DNA and can multiply on their own inside the cell

26. Chloroplasts • Algae and green plants • Membrane enclosed structure containing the pigment Chlorophyll and enzymes for photosynthesis • Flattened membrane disks call Thylakoids • Like mitochondria, contain 70s ribosomes, DNA and can multiply on their own inside the cell

27. Peroxisomes • Similar to Lysosomes • Single membrane containing enzymes that oxidize various organic molecules, such as lipids and amino acids. • During this metabolism, the toxic product, H2O2 is formed, so peroxisomes also contain high levels of the enzyme catalase

28. Centrioles • Located near the nucleus • Important for the organizing of the mitotic spindle apparatus during cell division and for microtubule formation in non-dividing cells