The cytoskeleton and the mitochondria- week 4

Question 1

Explain how ATP and similar molecules are able to store and release energy.

Answer 1

• the ATP molecule splits off one of its three phosphates, becoming ADP (Adenosine di-phosphate) + phosphate
  -chemical energy is stored in the pyrophosphate bond, which lies between the last two phosphate groups of ATP.

Question 2

Define the meaning “electrochemical gradient” and apply this to explain its link with electrons transport.

Answer 2

-the transfer from lower to higher electron affinity which is energetically favourable.
-the energy released is used to pump hydrogen ions into the intermembrane space so now it becomes +vely charged compared to the matrix- the dumping of hydrogen ions generates an electrochemical gradient across the inner mitochondrial membrane

Question 3

Discuss the way the electrochemical gradient is linked to ATP synthesis.

Answer 3

the electrochemical gradient allows for the hydrogen ions in the intermembrane space to go down their electrochemical gradient through ATP synthase to produce ATP

Question 4

Summarise how the various substrates and products of the processes that occur within the mitochondria are transported in and out.

Answer 4

• By electrochemical gradient: pyruvate & inorganic phosphate transport is driven by H+ gradient- they are co-transported in the same direction
  -By voltage Gradient:
  Co-transport of ATP out & ADP in mitochondria matrix (ATP has -4charge and ADP has -3 charge)- overall net charge of 1- in the intermembrane space.
  -oxygen & CO2 diffuse down their conc gradient

Question 5

what is the chemical formula of the final electron acceptor accepts the electrons

Answer 5

2H+ + 1/2O2 + 2e- –>H20

Question 6

Summarise the way mitochondrial and chloroplast proteins which are synthesised in the cytoplasm are transported into these organelles (& compare to other organelles).

Answer 6

-Most proteins destined for the mitochondria (and chloroplasts) are encoded in the nucleus and are produced by cytosolic ribosomes.
-Translocases of the Outer (TOM) and Inner (TIM) Mitochondrial membranes mediate passage into the mitochondria: Proteins can pass through one (TOM) or both translocases to become localised to either the inter membrane space or the matrix

Question 7

Recall that chloroplasts and mitochondria possess their own genetic systems and relate this to the evolution of eukaryotic cells.

Answer 7

-both mitochondria and chloroplast process their own genetic system, as their genomes are circular.
-transcription & translation occur in the matrix/stroma
-there are several DNA copies per organelle & most mitochondria and chloroplast DNA is maternally inherited (only inherit the mitochondrial DNA from our mothers)

Question 8

what is the evidence of evolution of mitochondria and chloroplast

Answer 8

-separate genetic system
-the way in which theses organelles form- aren’t synthesised from scratch they grow and divide instead like a cell

Question 9

Name the three types of cytoskeletal elements, in size order.

Answer 9

• Microtubules
• Intermediate Filament
• Actin filaments

*intermediate Filament is smaller than microtubules but larger than actin filaments

Question 10

describe the main features(i.e. whats it made up of/structure) and roles of Actin Filaments

Answer 10

Actin filaments: made up of globular protein actin which assembles into 2 stranded helical polymers. Role is in cell shape, allows cells to move as they don’t have a flagellum

Question 11

describe the main features and roles of Microtubules

Answer 11

Microtubules; made up of globular protein TUBULIN- forms hollow tubules. Role is positioning organelles, intracellular transport & mitosis when wanting to separate the genetic material in 2 different polls

Question 12

describe the main features and roles of Intermediate Filament

Answer 12

Intermediate Filament: made of various intermediate filament proteins-rope like fibres. Role is in mechanical support of the cell structures.

Question 13

Explain why the cytoskeleton can assemble and disassemble rapidly.

Answer 13

-as monomers from end-to-end & side interactions relative strengths determine mechanical properties.
-interactions are non-covalent: rapid assembly as there are no bonds to break
-Rate of monomer addition relative to monomer concentration, rate of disassembly is constant-net growth is dependent on monomer availability

Question 14

Explain how actin filaments and microtubules can grow and shrink and they have fast and slow growing ends.

Answer 14

when subunits attach to the fast end their conformation changes -gives fast end a higher affinity for monomers than the slow end and the addition to the filament ATP –> ADP as the actin monomers carry an ATP molecule

Question 15

Name the motor proteins which move along actin filaments and microtubules

Answer 15

Myosin motors move on actin filaments, whereas kinesin and dynein motors move on microtubules. (These molecular motor proteins all convert the energy from ATP into force and movement on either the actin or microtubule tracks.)

Question 16

Discuss the way that myosins move along actin filaments; describe how this is involved in muscle contraction.

Answer 16

Attached – myosin head bound to actin filament
Release – myosin binds ATP and releases actin
Cocked – ATP hydrolysis cause a conformation change
Grip – reattachment to actin and phosphate release
Pull – conformation change and ADP release

Question 17

Describe how kinesins is involved in transporting vesicles.

Answer 17

vesicles which are attached to scaffolding proteins which allow for dynesis to attach the vesicle to the microtubule which can be transported along microtubules: e.g. those travelling from the ER to the Golgi are moved by dynein (towards - end).
* DYNESIN IS IMPORTANT TO ATTACH THE KINESIN which then kinesin will walk it along
—->Dynein will transport things from the ER to the Golgi and Kinesin will transport things from the Golgi back to the ER
this transport can also happen along actin filaments

Question 18

what are the steps of how kinesis moves along microtubules (4 steps)

Answer 18

Step 1 – Leading head (1) bound to tubulin (monomers which assemble into microtubules) Trailing head (2) is already bound to ADP
Step 2 – Head 1 binds to ATP causing conformation change which throws head 2 forward
Step 3 – Head 2 binds tubulin
Step 4 – Head 2 releases ADP which allows for an ATP molecule to bind to the nucleotide binding site (it hydrolyses ATP)

Question 19

Outline how the actin and tubulin cytoskeletons are involved in cell motility(moving). (3 ways)

Answer 19

–CELL CRAWLING: Involves rearrangement of the actin cytoskeleton by:
* Protrusion: actin fibres form at the leading edge (like an extension at the front of the cell)
* Attachment: the actin cytoskeleton attaches to the surface across the cell
membrane at focal points
* Traction: myosins pull the trailing cytoplasm forward
–FLAGELLA (and Cilia) – e.g. sperm
* Tubular structures composed of microtubules, the motor activity of ciliary dynein causes for the microtubules to slide across form one another in the flagella- causes cell to propel
–>MICROVILLI – e.g. in the gut epithelium
* Bundles of actin filaments extend to the tip, Myosins attached to the cell membrane walk along the actin filaments, causing the microvillus to wave

Question 20

what are the differences of kinesis and dyneins

Answer 20

Kinesin moves from the - to + end of the microtubule…while dyneins move in the opposite direction
(+ to -)

Question 21

what are kinesin and dyneins

Answer 21

they are microtubular motor proteins they have globular heads which interact
with the cytoskeleton (Like myosins)

Question 22

what is the cytoskeleton

Answer 22

its a filamentous structure which is found through the cytoplasm and nucleus. its formed of protein monomers which assemble into repeat structures

Question 23

where does the microtubule end

Answer 23

in the centrosome
and in the opposite way the microtubule leads to the plasma membrane

Question 24

In the Electron Transport Chain the electrons pass through a series of complexes with increasing _____. This transfer is energetically _______and the extra energy is used to pump ______into the ______.

Answer 24

1)(electron affinity, redox potential)
2) (favourable)
3) hydrogen ions
4) intermembrane space

*Electrons enter the electron transport chain and are passed through a series of complexes, each of which has a higher affinity for them then the previous

Question 25

Which of these has the highest electron affinity?
1)Oxygen

2)NADH dehydrogenase complex

3)Cytochrome b-c1 complex

4)Ubiquinone

5)NAD+

Answer 25

1
*Oxygen is the final acceptor in the electron transport chain and therefore it has the highest electron affinity

Question 26

What is the pH of the mitochondrial matrix?
What is the pH of the intermembrane space?

Answer 26

1)8
2)7

Question 27

An enzymatic complex called ___found in the ___ membrane of the mitochondria forms a hydrophilic path through which _____ can flow.

The direction of flow is from the ___ to the _____ {name the compartments} and is therefore down the concentration gradient and hence energetically this is favourable.

The transmembranous domain of the enzyme complex is forced to _____ rather like a _____

As an attached stalk grinds against the enymatic head the _____ energy is converted to ___ energy in the reaction:
ADP + Pi → ATP

Answer 27

1) ATP synthase
2) Inner
3) Hydrogen ions
4) Intermembrane space
5) matrix
6) rotate
7) water wheel
8) mechanical
9) chemical

Question 28

Identify the sites of the following:-
1.ATP synthase
2.pyruvate transporter
3.Mitochondrial DNA
4.Citric Acid Cycle
5.Porins
6.Electron Transport Chain
7.Glycolysis

Answer 28

1. inner membrane
2. inner membrane
3. Matrix
4. Matrix
5. Outer membrane
6. inner membrane
7. cytoplasm

Question 29

Where are mitochondrial proteins synthesised?

Answer 29

mitochondrial Matrix

Question 30

Name one toxin or drug which affects the assembly or disassembly of the cytoskeleton.

Answer 30

Taxol, Colchicine, Latrunculin, Phalloidin, Vinblastine, Vincristine

Question 31

Microtubules and actin filaments have a fast growing and a slow growing end. Name two mechanisms by which this is achieved.
1. Glycosylation
2. Nucleotide hydrolysis
3. Conformation change
4. Phosphorylation
5. Covalent attachment

Answer 31

2 & 3

Question 32

Within the cytoskeleton what is the concentration at which the rate of monomer addition equals the rate of removal known as?

Answer 32

the critical concentration

Question 33

Typically microtubules are attached to one point within the cell; what is it called?

Answer 33

centrosome

Question 34

When kinesins move along microtubules, after the trailing head has been thrown forward what enable the new trailing head to be released from the microtubles?

Answer 34

ATP hydrolysis by the new trailing head

Question 35

Cytoskeletal elements are central to cell motility. Match the form of motility to the element:
Muscle contraction
Flagella and cilia
Cell crawling
Microvilli in the gut

Answer 35

1) actin filaments
2) microtubules
3) actin filaments
4) actin filaments