Cells 2: Mitochondria, Chloroplasts, Cytoskeleton, Cell Adhesion

Question 1

Describe the mitochondria

Answer 1

• located in animal cells and plant cells
• have an outer and inner membrane (the inner membrane is folded and is called the cristae)
• where respiration takes place (citric acid cycle) which occurs in the matrix of the mitochondria

Question 2

Describe the chloroplast

Answer 2

• only in plant cells and is responsible for photosynthesis
• has a double membrane
• Carbon fixation occurs where sugars are made (in the Stroma), amino acids, and fatty acids
• has stacks of membranes called thylakoids

Question 3

What is the Endosymbiotic Organelles “Theory” and what kind of evidence proves this theory?

Answer 3

• states that mitochondria and chloroplasts are descendants of bacteria
  Evidence:
• they both have double membranes (likely taken up by endocytosis)
• has own genome and has genes more similar to eubacterial genes
• has own ribosomes and are more similar to Eubacteria
• Lipids come from ER through a unique system (unique machinery for protein import)

Question 4

Describe the cytoskeleton. How many cytoskeletal filaments are there are there, and what are they?

Answer 4

• keeps the shape of the cell and holds its fluid
• it is very crowded (had a mixture of proteins, RNA, ribosomes, etc)
• 3 cytoskeletal filaments (Actin, Intermediate, and Microtubules)

Question 5

Give a description of Actin Filaments (AKA microfilaments) and their function

Answer 5

• structure: strands in double helix
• maintain cell shape by resisting tension
• moves cells via muscle contraction or cell crawling
• divide animal cells in two
• move organelles and cytoplasm in plants, fungi, and animals
• Ex: Actin-Myosin Contraction

Question 6

Give a description of Intermediate Filaments and their function

Answer 6

• structure: fibers wound into thicker cables
• maintain cell shape by resisting tension
• anchor nucleus and some other organelles

Question 7

Give a description of Microtubules and their function

Answer 7

• structure: a hollow tube made our of alpha- and beta-tubulin dimers
• maintain cell shape by resisting compression
• move cells via flagella or cilia
• move chromosomes during cell division
• assist formation of cell plate during plant cell division
• move organelles
• provide tracks for intracellular transport
• Ex: Cilia

Question 8

Describe the Extracellular Matrix (ECM)

Answer 8

• the most important function of the extra cellular matrix is to help stabilize the cell
• ECM contains collagen proteins which consist of three polypeptide chains that wind around each other (cartilage)

Question 9

In cells, what are adhesion sites called, and give an example?

Answer 9

• Focal Adhesions
• Ex: Integrins are long structures that integrate into the cellular membrane and attached to fibronectin/collagen outside the cell and the actin filaments inside the cell (connect the inside of the cell with outside environment)

Question 10

Describe Cell-Cell Adhesion

Answer 10

• in cell recognition, one cell specifically binds to another cell of a certain type which leads to phagocytosis, DNA exchange, or sperm-egg fusion
• in cell-cell adhesion, cells stably bind to each other

Question 11

Name the four types of cell-cell junction and give

Answer 11

• tight junction
• adherens junction
• desmosome
• gap junction

Question 12

Function of a tight junction

Answer 12

• seals neighboring cells together in an epithelial sheet to prevent leakage of molecules between them
• separates membrane domains to ensure proper parts of cells stay on appropriate sides

Question 13

Function of adherens junction

Answer 13

• join actin bundle in one cell to a similar bundle in a neighboring cell

Question 14

Function of a desmosome

Answer 14

• joins the intermediate filaments in one cell to those in a neighbor

Question 15

Function of a gap junction

Answer 15

• allows the passage of small water soluble ions an molecules in the cytosol
• low molecular weight molecules can freely diffuse from one cell to the next