The Cell: Part 4: The Cell Organelles

Question 1

The Nucleus

Answer 1

Contains Chromosomes made of DNA wrapped in proteins called Histones into a chromatin network. The chromosomes contain genes: bits of DNA that code for polypeptides.

Question 2

The Nucleolus

Answer 2

• A prominent region in the nucleus that is not dividing. -Non membrane bound organelle.
• Tangles of chromatin and unfinished bits of ribosomes
• Where components of ribosomes are synthesized.
• One or two or usually visible.

Question 3

Ribosomes

Answer 3

• Suspended freely in the cytoplasm or bound to the endoplasmic reticulum.
• Made of ribosomal RNA and proteins.
• Protein synthesis site.

Question 4

Endoplasmic Reticulum

Answer 4

• A system of membrane channels that transvers the cytoplasm.
• Rough ER: Studded with ribosomes because it is the site protein synthesis as well as transport throughout the cytoplasm.
• Smooth ER: Synthesizes steroid hormones and other lipids. Detoxifies the Cell. Connects Rough ER to Golgi Apparatus. Carbohydrate (Glycogen) metabolism.

Question 5

Golgi Apparatus

Answer 5

• Lies near the nucleus and is surrounded by vesicles.
• Consists of flattened sacs membranes stacked to each other.
• Its function is to package, store, and modify substances produced in the rough ER. These substances are secreted to other parts of the cell and to the cell surface for export to other cells.

Question 6

Mitochondria

Answer 6

• Site of cellular respiration.
• All cells have mitochondria. A very active cell contains around 2500 of them.
• Outer Double membrane.
• Contains folded inner membranes called cristae: enzymes that are important to the cellular respiration and are embedded in the cristae membrane.
• Contains its own DNA and can self-replicate.

Question 7

Vacuole

Answer 7

• Single membrane bound structures.
• Plant cells and some specialized animal cells(fat or adipose).
• Fresh water Protista like paramecium and amoeba have contractile vacuole that pumps the excess water out of the cell.
• store substances for the cell.

Question 8

Vesicles

Answer 8

• Tiny Vacuoles.
• Found in many places in the cell including the axon.
• Release neurotransmitters into a synapse.

Question 9

Plastids

Answer 9

-Double membrane.
-Only in plants and algae.
-Divided into parts: Chloroplasts, Leucoplasts, and Chromoplasts.
_Chloroplasts:
-are green because they contain chlorophyll.
-sites of photosynthesis.
-double outer membrane.
-Have inner membranes that form a series of structures called grana that lies in the stroma.
-Contain its own nuclear material and can replicate itself.
=Leucoplasts:
-Colorless.
-store starch.
-found in roots (turnips) and tubers (potatoes).
=Chromoplasts
-store carotenoid pigments
-responsible for the red-orange coloring in carrots and many other vegetables.
-Its bright colors attract pollinators.

Question 10

Cytoskeleton

Answer 10

• A complex network of protein filaments that extends throughout the cytoplasm.
  -Gives the cell its shape and helps it move.
  -Includes two types of structures: Microtubules and microfilaments.
  =Microfilaments:
• Made of the protein Actin.
  -Help support the shape of the cell.
  -Enable the animal cells to form the cleavage furrow during cell division.
  -Enable Amoeba to move by sending out pseudopods.
  -Enable the skeletal muscles to contract by sliding along myosin filaments.
  =Microtubules:
  -Made of protein Tubulin.
  -Thick hollow tubes that make up cilia, flagella, and spindle fibers.

Question 11

Centrioles and Centrosomes

Answer 11

• Lie outside the nuclear membrane.
• Organize spindle fibers for cell division.
• Found only in Animal cells.
• Plants have a single microtubule organizing area instead.
• Two centrioles at right angles of each other make up a centrosome.
• Centrioles and spindle fibers have the same structures.
• Centrioles= 9 triplets
• Cilia +flagella= 9+2

Question 12

Cilia and Flagella

Answer 12

• Cilia= 9 pairs
• Flagella= 2 singlets
• Made of microtubules.
• Same internal structures.
• The only difference is in the length: Flagella are long, Cilia is short.

Question 13

The Cell Wall

Answer 13

• In plant cells, the cell wall is located outside the plasma membrane.
• Cell walls of fungi are made of Chitin.
• Not found in Animal Cells.
• Plant’s and Algae’s Cell walls are made of cellulose.
• When a plant cell divides, a thin layer is formed called Middle Lamella: it keeps the two daughter cells attached.
• Some cells produce a second cell wall underneath the primary one called secondary cell wall.

Question 14

Cytoplasm and Cytosol

Answer 14

• Cytoplasm: the entire area between the nucleus and the plasma membrane.
• Cytosol: a semiliquid portion of the cytoplasm.
• In eukaryotic cells, organelles are suspended in the cytosol and get carried around as the cytoplasm cycles around the cell in a process called cyclosis.

Question 15

Cell or Plasma Membrane

Answer 15

• A selectively permeable membrane that controls what enters and leaves the cell.
• Described as the fluid mosaic because it is made of many small particles that are able to move around and control what enters and leaves the cell.
• Consists of a phospholipid bilayer with proteins dispersed throughout.
• Molecules of cholesterol are embedded within the membrane making it less fluid and more stable.
• The external surface of the plasma membrane has carbohydrate chains attached to it. (Important for cell to cell recognition).
• An average cell membrane consists of 60% protein. They provide a lot of functions like membrane proteins, like ATP synthetase, that act as enzymes.