2A - Membrane Bound Organelle and Defining Characteristics of Eukaryotic Cells

Question 1

Describe the function of the nucleus.

Answer 1

This double membrane organelle not only stores DNA, but is the site of replication and transcription of genes as well. Within the nucleus, there is another membrane bound region called the nucleolus where rRNA are made

Question 2

The nucleolus is allows for rRNA to be made within its space. Why is this important?

Answer 2

This falls under the large concept of separation of functions as a result of membrane presence. This is important in separating the functions of rRNA synthesis from mRNA and DNA replication

Question 3

Elaborate the how the nuclear envelope works and what important structure lies within this membrane.

Answer 3

The nuclear membrane allows for the separation of functions of the cell from the nucleus. Due to how impermeable this structure is compared to a regular plasma membrane, the nuclear membrane contains nuclear pores to regulate its transport

Question 4

How does the endosymbiotic relationship of the mitochondria explain certain characteristics of the mitochondria today.

Answer 4

The endosymbiont relationship theory - the theory in which an aerobic prokaryote endocytosis an anaerobic prokaryote is often used to describe the characteristics it has today. (1) It explains how it has double layered membranes (2) semi autonomy - the ability for the mitochondria to replicate its own DNA without the extranuclear/cytoplasmic inheritance

Question 5

How is the mitochondria correlated to apoptosis?

Answer 5

The release of the enzymes from the inner membrane of the ETC triggers apoptosis. This means there is a causal relationship between the 2

Question 6

Which portion of the aerobic respiration takes place in the mitochondrial matrix?

Answer 6

This is where the H+ ions are pumped into when the ETC is active. This collection allows for a gradient to exist, which drives the production of ATP when the H+ flows along its electrochemical gradient

Question 7

The Krebs cycle occurs in which portion of the mitochondria?

Answer 7

The intermembrane space, therefore in between the outer mitochondrial membrane and the inner mitochondrial membrane

Question 8

You’re studying with a friend and she says that the ETC occurs in outer membrane. What is your response to this statement?

Answer 8

This is a false statement. The ETC is located in the convoluted cristae of the inner mitochondrial membrane

Question 9

The existence of the outer membrane creates what kind of space in the mitochondria?

Answer 9

This space is defined as the intermembrane space.

Question 10

The inner membrane creates what kind of space in the mitochondria?

Answer 10

This is called the mitochondrial matrix/space

Question 11

What is the inner membrane of the mitochondria made of?

Answer 11

The inner membrane of the mitochondria is made of very little cholesterol and high concentrations of cardiolipin

Question 12

In terms of permeability, compare the outer membrane of the mitochondria from the inner membrane.

Answer 12

The outer membrane of the mitochondria is highly permeable compared to the inner membrane. This is due to the large pores found on the membrane - these are essential to allowing proteins and solutes in and out of the intermembrane space

Question 13

What types of molecules are found in the lysosome?

Answer 13

These are hydrolytic enzymes called acid hydrolases. These enzymes have the ability to digest many things such as waste and engulfed particles. This is why the membrane of the lysosome is essential to keep these proteins away from the cell

Question 14

What important organelle functions in conjunction with the lysosome?

Answer 14

Endosomes - these are vesicles that transport substances throughout the cell such as the golgi apparatus, cell membrane and lysosome.

Question 15

Besides from the mitochondria, the break down of what other organelle triggers apoptosis of the cell?

Answer 15

The breakdown of lysosomes lead to the release of its hydrolytic enzymes. These hydrolases directly digest the components of the cell unlike the release of mitochondrial protein release. The release of mitochondrial proteins are indirect to apoptosis and do not directly digest the components of the cell

Question 16

What pH activates the enzymes of the lysosome?
A. 7
B. 6
C. 5
D. 4

Answer 16

C. 5. 5.2 to be exact!

Question 17

How is the endoplasmic reticulum related to the nucleus?

Answer 17

The ER is a direct continuation of the nuclear envelope, therefore this organelle is simply a single layer of phospholipid only unlike the nucleus itself which is a double layer membrane

Question 18

What are the invaginations of the golgi and endoplasmic reticulum called?

Answer 18

Nothing, these have no particular names like the invaginations of the mito. The mitochondria invaginations are called cristae, but cristae can not be applied to the the golgi and ER

Question 19

What is the function of rough endoplasmic reticulum?

Answer 19

The rough endoplasmic reticulum contains ribosomes on its membrane. This means, the RER plays a crucial role in not just translating proteins, but also in modifying proteins as well.
This modification of the RER is why it is part of the endomembrane system, which is a large system composed of organelles responsible for modifying and transporting proteins to its destination.

Question 20

The endomembrane system is composed of what?

Answer 20

The endomembrane system, which is a large system composed of organelles responsible for modifying and transporting proteins to its destination. These organelles are made of the golgi apparatus, lysosome, RER, and vesicles.
This is a system made of organelles important in post modification of proteins of proteins.

Question 21

During the production of insulin, the polypeptide is cleaved into its mature form and secreted from the cell. The cleavage mostly likely occurs where?

Answer 21

In the endomembrane. In this system, modification to proteins, such as cleavage, occurs within the RER or Golgi. Proteins entering into the endomembrane system are usually secreted or incorporated into the cell membrane. Whereas proteins made in the cytosol through free floating ribosomes typically are not modified further. Proteins released made in the cytosol will be released into the cytosol only.

Question 22

While the endoplasmic reticulum is a direct continuation of the nucleus, how is the ER different from the nucleus?

Answer 22

The nucleus is a site of storage of DNA and where DNA & genes are regulated and transcribed/replicated
The ER, unlike the nucleus has other functions: lots of invagination, studded with ribosomes (RER), translated mRNA transcribed from the DNA - RER, and SER: synthesis carbohydrates & Lipids detoxifies cells of toxins

Question 23

Which portion of the ER is important in the endomembrane system? Why?

Answer 23

The RER is important to the endomembrane system as this organelle plays a role in postmodifying and transporting proteins

Question 24

List the functions of the smooth endoplasmic reticulum.

Answer 24

It has many functions:

(1) Synthetic: Carbs, Lipids, and steroid hormones
(2) Detoxification
(3) Storage of Ca2+

Question 25

How does the Smooth ER have a role in the cellular membrane?

Answer 25

The smooth endoplasmic reticulum produces lipids such as phospholipids which are essential components of the cell wall

Question 26

Which of the following organelles is responsible for synthesizing a phospholipid?
A. Rough Endoplasmic Reticulum
B. Golgi Apparatus 
C. Liver 
D. Smooth Endoplasmic Reticulum

Answer 26

D. Smooth Endoplasmic Reticulum. The SER is responsible for synthesis of lipids, carbohydrates, & steroid hormones, Ca2+ ion storage, and detoxification of toxins.

Question 27

Which of the following is NOT a function of the smooth endoplasmic reticulum?
A. Ca2+ ion storage
B. Detoxification of toxins
C. Addition of signal sequence to proteins
D. Synthesis of carbohydrates

Answer 27

C. This is done in the endomembrane system by RER and Golgi Apparatus

Question 28

What structural difference is SER prevents it from being a part of the endomembrane system.

Answer 28

The lack of proteins in SER doesn’t allow the organelle to translate protein. Therefore it is not able to modify proteins like the RER

Question 29

Some organelles in eukaryotic cell are considered to have a double membrane. What does this mean? What organelles have these?

Answer 29

This means that the organelle has 2 layers of phospholipid bilayer. This double membrane creates 2 unique spaces within the organelle, which separates functions within the organelle. These double membrane are thought to have at one point been established due to endosymbiosis. These organelles include: the nucleus, mitochondria and chloroplast

Question 30

What types of organelles are considered single membrane structures?

Answer 30

Single membrane structures are any structure which has only a single phospholipid bilayer. These include the plasma membrane, the rough endoplasmic reticulum, etc.

Question 31

The endoplasmic reticulum is an extension of the nucleus. However, the ER is not a double membrane like the nucleus. Why is this the case?

Answer 31

The ER is an extension of 1 phospholipid bilayer of the nucleus - the nuclear envelope - only the inner membrane (of the nucleolus) does not extend to create the ER. This is why the ER is made of 1 phospholipid bilayer.

Question 32

The cell membrane is a phospholipid bilayer. Is this a double membrane?

Answer 32

No, while the phospholipid bilayer of 2 phospholipid heads facing the external and hydrophobic tails facing inward, a double membrane composes 2 sets of phospholipid bilayer. This is why the cell membrane is not a double membrane as it only has 1.
[common misconception; review if needed]

Question 33

Describe the mechanism of protein modification achieved by the rough endoplasmic reticulum

Answer 33

Mechanism of protein modification:

1. mRNA sequence diverts protein to dock at ribosomes of RER. These are called signal sequences
2. Ribosomes transfer newly synthesized proteins into the lumen of the RER
3. Lumen - is the site of protein modification such as folding, addition of side chains, etc.
4. Proteins are then directed to final destination if they are not destined to stay in the RER. These tend to be transported through vesicles to their location: organelle, organelle membrane, secretion, etc.

Question 34

Signal sequences direct the mRNA to the RER. At what point is this specific signal sequence cleaved?

Answer 34

This sequence is cleaved inside the RER after it is translated through the ribosome into the RER

Question 35

What are signal sequences made of?

Answer 35

Those that direct the mRNA to the RER are made of RNA bases

Question 36

After being transcribed, a mRNA is directed to the RER and docks. How is this information able to reach the inside of the RER?

Answer 36

Once the mRNA docks, it is transcribed through a transmembrane ribosome and the protein chain is thus deposited into the lumen inside of the RER.

Question 37

Compare and contrast the protein modifications of the RER from the golgi apparatus?

Answer 37

RER: Addition of side chains, folding of proteins, cleaving of sequences such as signal sequences.
Golgi: Addition of carbs, Pi, SO42-, or signal sequences

Question 38

A protein made in by the RER is not destined to stay in the RER. What must occur in order for it to reach its destination?

Answer 38

The protein must be packaged into a vesicle

Question 39

What similarities are shared bt the RER and golgi after a protein is modified within each organelle?

Answer 39

If the proteins are not destined to stay within the organelle, booth are packaged into vesicles in preparation of transport.

Question 40

At what point of protein synthesis does protein reach the golgi apparatus?

Answer 40

Proteins are transferred to the golgi after it has been translated by the RER. They reach the golgi after they are packaged into vesicles.

Question 41

What type of modifications does the golgi do to proteins?

Answer 41

Addition onto the protein such as: Phosphate groups, sulfate groups, carbohydrate side chains, or addition of signal sequences

Question 42

How is the golgi apparatus similar to the RER in terms of transport?

Answer 42

The golgi and RER packages the protein into vesicles before the proteins are transported to their final location

Question 43

Describe the notable features of the golgi apparatus.

Answer 43

Cis face - this is the side of the golgi in which vesicles from the RER docks and deposits proteins into the golgi
Trans face - this is the side of the golgi in which post modified proteins leave the the golgi in vesicles.
Cisternae - these are invaginations of the golgi

Question 44

What functions are achieved by the peroxisomes?

Answer 44

Peroxisomes commit to many things:

1. Breakdown of fatty acids via β-oxidation
2. Detoxification of toxins, poisons, and hydrogen peroxide (into H2O and O2 via catalase)
3. Uses H2O2 to dump electrons for FADH2

Question 45

How is the golgi and lysosome linked?

Answer 45

The golgi apparatus is responsible for the formation of lysosome. When vesicles bud off from the trans-golgi AND these vesicles fuse with endosomes and this forms lysosomes!

Question 46

How is the ER and lysosome linked?

Answer 46

The enzymes of the lysosome (hydrolases) are made in the RER. These proteins are then transported to the ER and tagged by the golgi to be inserted into the lysosome.

Question 47

The signal sequence tagged by the golgi onto enzymes destined for the lysosome are
A. Lactose-5-phosphate 
B. Mannose-6-phosphate
C. Fructose-3-phosphate
D. Cholesterol

Answer 47

B. Mannose-6-phosphate. Can remember this signal sequence by thinking about the structure of the tag. This is a carb, therefore not cholesterol, and its a 6 phosphate