Chap 3 Cell Organelles

Question 1

Why are eukaryotic organelles surrounded by a membrane?

Answer 1

To allow multiple metabolic processes to happen simultaneously inside the cell.

Question 2

Name all the membrane bound and non membrane bound organelles.

Answer 2

Membrane Bound:Nucleus,mitochondria,golgi apparatus,smooth and rough ER,lysosome
Non Membrane Bound: Ribosome,cytoskeleton,centrosomes

Question 3

Explain the characteristics,structure and functions of the nucleus.

Answer 3

The nucleus is the genetic control center of the cell, it is the largest organelle and is surrounded by a nuclear envelope/membrane that separates the cytoplasm from the nucleoplasm. The nuclear envelops contain nuclear pores that control and act as passageways for materials entering or exiting the nucleus.The nucleus contains the nucleolus and DNA.

Question 4

Explain the structure and characteristics of chromosomes.

Answer 4

Chromosomes are composed of DNA molecules bound to proteins called histones. Chromosomes are only present when the cell is ready to divide.

Question 5

Explain the structure and function of the nucleolus.

Answer 5

Nucleolus is a dense cluster of RNA and proteins that manufacture ribosomes. Nucleolus manufacture ribosomes that move out to position on the rough ER where they are used for protein synthesis.

Question 6

What is the difference between the DNA of prokaryotes and eukaryotes?

Answer 6

Eukaryotic DNA is surrounded by a membrane in the nucleus and is protected by histone proteins. Prokaryotic DNA is not enclosed in a nucleus and is not protected by histones.

Question 7

Explain the formation of chromosomes as well as the describe the structure and functions of telomeres and centromeres.

Answer 7

Chormosomes are formed as DNA wraps around histone proteins to form chromatin fibers. Chromatin fibers are tightly packed along with other proteins to form chromosomes. Telomeres are repeat sequences at the end of chromosomes that act as buffer sequences to protect DNA during replication. Centromeres are the sites where 2 sister chromatids attach (sister chromatids are exact copies of DNA formed after DNA replication.

Question 8

Describe what a ribosome is.

Answer 8

Ribosomes are round small minute particles made up of RNA and protein that is found in the cytoplasm of living cells.

Question 9

Describe how a glycoprotein is formed and transported out of the rough ER.

Answer 9

Translation occurs at the ribosomes along the rough ER to form a polypeptide chain within the ER. The polypeptide is then formed into a glycolipid being attached with sugar chains.The glycoprotein then buds off from the membrane of the ER in a transported vesicle and is thus secreted.

Question 10

What is the function of the rough ER?

Answer 10

Synthesis and transport of proteins. Proteins secreted from the rough ER are either transported to other organelles or are inserted into the membrane.

Question 11

Describe the structure and functions of the smooth ER.

Answer 11

The smooth ER is made up of interconnecting network of tubular membrane components.The smooth ER functions are:

1. Synthesis of lipids,steroids (e.g. sex hormones, testosterone estrogen)
2. Processes toxins and drugs in liver cells.
3. Stores and release calcium ions in muscle cells (sarcoplasmic reticulum) important in conduction of contraction stimulus.

Question 12

Describe the structure,function and characteristics of the golgi apparatus.

Answer 12

Golgi apparatus is made up of stacks of membranous sacks called cisternae, they have a cis face which is the side that new transport vesicles come from and a trans face where transport vesicles are secreted from the golgi. Golgi apparatus receives and modifies ER products (proteins,lipids,carbohydrates) and then either ship them to other organelles or the cell surface.Its is considered the finishing factory of the cell.

Question 13

Explain the Protein Secretion Pathway starting from the nucleus.

Answer 13

Information coded in DNA sequence is transcribed to mRNA in nucleus.The mRNA leaves the nucleus through nuclear pores to the cytoplasm where it is translated in the ribosomes on the rough ER and the protein is synthesized inside the ER.Proteins synthesized in the ER are transported via transport vesicles to the Golgi Apparatus. Transport vesicles fuse with the golgi apparatus where the proteins are modified.The final modified protein products are packed into secretory vesicles that bud off from the golgi apparatus.Some vesicles remain inside the cell for internal use while others move to the cell surface and fuse with the cell membrane releasing their products via exocytosis.

Question 14

Explain the formation and secretion of insulin.

Answer 14

Insulin is synthesized in the rough ER as a large inactive protein known as proinsulin. It is then transported via transport vesicles to the Golgi where it is cut down to its final size and is secreted in secretory vesicles.Secretory vesicles then fuse with the plasma membrane and release insulin into the bloodstream via exocytosis.

Question 15

How is the lysosome formed and explain its structure.

Answer 15

Lysosomes are sacs that store hydrolytic enzymes for the digestion of food and other substances. Lysosome are vesicles that are formed by proteins (the digestive enzymes) that are modified,packaged and bud off from the Golgi Apparatus.

Question 16

Explain the functions of lysosome.

Answer 16

1. Lysosomes digest invading or ingested bacteria in WBCs.
2. They digest and recycle debris and old worn out cell organelles and bacteria.
3. Causes cell death by lymosomal membrane permeabilization where the contents of the lysosome are leaked (e.g. cathepsin proteases).This helps the survival of organisms as it prevents cancers.

Question 17

Explain the function of peroxisomes.

Answer 17

1. Peroxisomes breakdown hydrogen peroxide which can be harmful to the cell to H20 and 02 by use of the enzyme catalase.
2. Peroxisomes break down long fatty acid through beta oxidation into medium length fatty acid chains.This produced hydrogen peroxide that is later decomposed by catalase. The medium chain fatty acids are subsequently broken down to carbon dioxide and water in the mitochondria
3. Peroxisomes also aid in biosynthesis of lipids(cholesterols) and bile acids.

Question 18

Explain Metabolism,Catabolism and Anabolism.

Answer 18

Catabolism is the breakdown of complex molecules to produce energy and molecular building blocks
Anabolism is the usage of energy and molecular building blocks to build cells and cell components.
Metabolism = Catabolism + Anabolism

Question 19

Explain characteristics of the mitochondria.

Answer 19

Mitochondria are the powerhouse of the cell and generate ATP.They are rich in enzymes responsible for catabolism. They are membrane bound structures found in the cytoplasm.

Question 20

Explain the structure of the mitochondria and the functions of these structures.

Answer 20

Mitochondria structure is made up a double membrane.The outer membrane is smooth while the inner membrane is highly convoluted forming folds called cristae. Cristae increase the inner membrane’s surface area and contains many ATP Synthase enzymes which catalyse catabolic reactions.

Question 21

What are some factors that lead Lynn Margulis to hypothesise that mitochondria evolved from bacteria?

Answer 21

1. Mitochondria are about the same size of bacteria.
2. They contain their own DNA and ribosomes
3. Their ribosomes contain the same structure as those in bacteria not like those in eukaryotes.
4. Mitochondria can divide on their own.

Question 22

Explain the Endosymbiont hypothesis for mitochondria.

Answer 22

The hypothesis suggests that a larger prokaryote or early eukaryote engulfed a small prokaryote many years ago.These two may have lived in symbiosis eventually evolving into modern eukaryotes with mitochondria.This is also suggested for chloroplast as they have the same characteristics as mitochondria and bacteria.

Question 23

Explain what is the cytoskeleton.

Answer 23

Cytoskeleton is a network of protein structures that run through the cytoplasm. Cytoskeleton provides the cell with an internal framework and is made up of 3 elements: intermediate filaments,microfilaments and microtubules..

Question 24

What are the functions of the cytoskeleton.

Answer 24

1. Helps the cell to maintain shape
2. Strengthens the plasma membrane
3. Plays important roles in ameboid mobility,internal movement of cell organelles,muscle fiber contraction

Question 25

Explain the functions of centrosome and centrioles.

Answer 25

Centrosomes are where the microtubules are produced.
Centrioles are structures found within the centrosomes, each centrosome contains 2 centrioles. Centriols are important in the movement of chromosomes during cell division. Centrosomes make two copies of themselves during cell division leading to 2 centrosomes each with a pair of centrioles.

Question 26

Explain the function of centrosomes in cell division.

Answer 26

Centrosomes make 2 copies of themselves during cell division each with a pair of centrioles. During cell divison the centomeres move to the opposite ends of the nucleus. For each centrosome, microtubules grow into spindles that move the chromosomes to separate them into 2 daughter cells.

Question 27

What is the function of the central vacuole in plants.

Answer 27

Filled with fluid
Helps maintain pressure and shape of cell
Hold materials and wastes
Regulates composition of the cytoplasm.