Unit 1: Biochemistry (2.1)

1. Unit 1: Biochemistry (2.1) Structures and Functions in Eukaryotic Cells

2. Eukaryotic Cells • Animals, plants, fungi and protists are composed of eukaryotic cells. • All eukaryotic cells have the following in common: •  DNA contained within a membrane-bound nucleus •  a cell membrane comprised of a phospholipid bilayer •  jelly-like cytoplasm

3. Animal Cell

4. Plant Cell

5. Nucleus • Control centre of the cell • contains DNA/genes/chromosomes, which stores and replicates the genetic information • usually uncoiled (chromatin  a mixture of DNA and proteins)‏ and are only visible in dividing cells • The number of chromosomes varies from species to species

6. Nucleus cont’d • May contain an area called nucleolus containing RNA and proteins • Surrounded by the nuclear envelope – a dbl membrane to separate nucleus from the rest of the cell. The space btw the 2 membranes is called the lumen. • The membrane contains nuclear pore complexes which allow water and ions to pass freely, but regulate the passage of macromolecules and RNA • The nucleus directs cell division

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8. Endoplasmic Reticulum • The nuclear envelope is connected to and part of a complex of membrane-bound tubules and sacs called the endoplasmic reticulum (ER). • Made up of 2 parts: the rough ER and the smooth ER • Regions of the ER which synthesize proteins have ribosomes on their surface, hence the name RER. • It is here that proteins which are a part of membranes or intended for export from the cell are assembled (whereas proteins that function in the cytosol are made by ribosomes suspended there)

9. Smooth Endoplasmic Reticulum • Regions of the ER which do not have bound ribosomes are called smooth endoplasmic reticulum. • The SER synthesizes lipids and lipid-containing molecules such as phospholipids that make up membranes. • The SER also performs other functions depending on the type of cell. For example, the SER in liver cells help detoxify drugs and alcohol.

10. Endoplasmic Reticulum

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12. Ribosomes • Tiny organelles found in cytoplasm and attached to the endoplasmic reticulum • Composed of two subunits made of protein and RNA • No membrane • Function: makes RNA into protein • Found in both plant and animal cells • Eukaryotic ribosomes are different in structure compared to those of prokaryotes.

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14. The Golgi Apparatus • A stack of curved membrane sacs that packages, processes, sorts and distributes proteins, lipids, and other substances within the cell • Acts like a “post office” for the cell

15. The Endomembrane System • The endomembrane systemconsists of the nuclear envelope, the ER, the Golgi apparatus and vesicles. • This system synthesizes, modifies and transports proteins and other cell products. • This system also isolates individual parts of the cell so that particular functions are restricted to specific regions. • The organelles that make up the endomembrane system are connected to one another either directly or by transport vesicles.

16. Functions of the Endomembrane System • On the surface of the RER, polypeptides are produced by bound ribosomes and extruded into the lumen, rather than being released into the cytosol • These polypeptides travel through the lumen to the SER, where they are stored and processed. When they are ready for transport, pieces of smooth ER pinch off to form vesicles containing the protein.

17. Functions of the Endomembrane System • Vesicles from the smooth ER travel across the cell to the cis face (entry face)of the Golgi apparatus. There, the vesicles merge with the membrane of the Golgi and release their contents into the interior. In the Golgi, some proteins are stored and others are modified further. • When modified proteins are ready for transport, pieces of the Golgi apparatus pinch off from the trans face (exit face) to form vesicles. These vesicles transport the proteins to the cell membrane, or to other destinations within the cell.

19. Additional Functions of the Endomembrane System • Recall that the smooth ER is responsible for the creation and metabolism of lipids, including steroids and phospholipids that make up cell membranes and organelle membranes. The Golgi sorts, packages and distributes these lipids as well as proteins. • The Golgi also manufactures macromolecules, such as carbohydrates, like pectin, a polysaccharide found in cell walls. • In animal cells, the Golgi also produces lysosomes, which are membrane-bound sacs containing digestive enzymes.

20. LYSOSOMES

21. Lysosomes • Lysosomes contain more than 40 enzymes that break down macromolecules into smaller ones that can be reused by the cell. • They also break down parts of the cell that are old or no longer needed as well as bacteria and foreign particles that have been ingested by the cell.

22. Peroxisomes • Like lysosomes, but they are formed by breaking off of the ER. They break down excess fatty acids and hydrogen peroxide and participate in the creation of bile acids and cholesterol. • They contain different types of enzymes than lysosomes (which catalyze hydrolysis rxns). • The enzymes in peroxisomes break down many biological molecules and some toxic ones too. For example, the peroxisomes in liver cells oxidize and break down alcohol molecules.

23. Vesicles and Vacuoles • Vesicles are membrane-bound sacs used for the transport and storage of substances in the cell. They form by pinching off of cell and organelle membranes. They then fuse with cell and organelle membranes to release their contents. An animal cell typically contains many small vesicles; however, plant cells contain a single, large central vesicle called a vacuole. • This stores water, ions, sugars, amino acids, macromolecules and enzymes that break them down. The amount of water in the vacuole determines the turgor pressure of the plant cell, which causes the plant cell to be rigid.

24. Plant Cell

25. Cell Structures Animation – Review • http://www.youtube.com/watch?v=LP7xAr2FDFU&feature=related

26. Chloroplasts • The cells of eukaryotic organisms that carry out photosynthesis typically have one to several hundred chloroplasts • These organelles contain the photosynthetic pigment chlorophyll, which absorbs light energy to convert CO2 and H2O into energy-rich glucose. • Chloroplasts are filled with grana, which are stacks of chlorophyll-containing thylakoids. it is here that the sun’s energy is captured.

28. Mitochondria • All of the functions that a cell must perform need to be fuelled by an energy source. In eukaryotic cells, the mitochondria break down high-energy organic molecules (glucose) to convert stored energy into usable energy. • Mitochondria have a smooth outer membrane and a folded inner membrane, called cristae. The fluid-filled space of the inner membrane is called the matrix. • Both the mitochondria and chloroplasts contain some of their own DNA, which encodes some, but not all, of their own proteins.

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30. Cell Wall • Cells of plants, fungi and some protists have a cell wall to protect and support the cell. • It is generally made up of a combination of polysaccharides, glycoproteins, or both. • Plant cell walls are made up of cellulose and pectins whereas fungal cell walls are made of chitin.

31. Cytoskeleton • An internal network of protein fibres in all cells. The fibres of the cytoskeleton extend through the cytoplasm, providing structure and anchoring the cell membrane and organelles in place. • Vesicles and other organelles move along these fibres, which act like tracks. • Refer to Table 2.1 on p. 66 to learn about the different protein fibres that make up the cytoskeleton.

33. Centrioles • Found in animal cells and are generally absent in plant cells. • They are cylindrical structures that are composed of groupings of microtubules arranged in a 9+3 pattern. • They organize the assembly of microtubules during cell division. • They replicate during the interphase stage.

34. Centrioles cont’d

35. Cilia and Flagella • Are appendages that develop on the outside of some eukaryotic cells. If there are just 1 or 2 appendages, they are called flagella. If many shorter appendages are present, they are called cilia. • These structures are composed of an internal shaft of microtubules, covered with an outer membrane which is a continuation of the cell membrane.