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Cell Biology > Lecture 4 - Exam 3 > Flashcards

Lecture 4 - Exam 3 Flashcards

1
Q

What are protein kinases responsible for?

A

Protein kinases catalyze the transfer of a phosphate group from ATP to the side chains of serine and threonine (serine/threonine kinases) or tyrosine (tyrosine kinases) residues.
(When you see serine/threonine and tyrosine, think phosphorylation!!!)

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2
Q

What are protein phosphatases responsible for?

A

Catalyze the removal of phosphate groups from the same amino acids by hydrolysis.

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3
Q

Describe the regulation of glycogen breakdown by phosphorylation.

A

The binding of epinephrine (AKA=adrenaline) to its cell surface receptor triggers the production of cyclic AMP (cAMP), which activates cAMP-dependent protein kinase.
The cAMP-dependent protein kinase phosphorylates and activates phosphorylase kinase, which in turn phosphorylates and activates glycogen phosphorylase.
Glycogen phosphorylase then catalyzes the breakdown of glucose to glucose-1-phosphate.

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4
Q

Do proteins change?

A

YES KNOW THIS CONCEPT!!!

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5
Q

In the inactive state what does the cAMP-dependent protein kinase consist of?

A

The enzyme will consist of two regulatory and two catalytic subunits.

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6
Q

In the cAMP-dependent protein kinase, where does the cyclic AMP (cAMP) bind to?

A

cAMP binds to the regulatory subunits, inducing a conformational change that leads to their dissociation for the catalytic subunits, leaving the catalytic subunits enzymatically active.

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7
Q

Describe the nucleus.

A

The nucleus contains the genome, it is where DNA and RNA synthesis occur, it has a double membrane (inner and outer). It is the repository of genetic info and the cell’s control center.

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8
Q

Describe the typical eukaryotic cell carrying out many different chemical reactions.

A

A typical eukaryotic cell carries out thousands of different chemical reactions simultaneously, many of which are mutually incompatible**.

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9
Q

What are membrane enclosed organelles important for?

A

Important for isolating and organizing the cell’s chemical reactions.

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10
Q

Where does the synthesis of proteins begin?

A

Cytosol

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11
Q

What does the fate of a protein that is synthesized in the cytosol depend on?

A

The fate of any protein synthesized in the cytosol depends on its amino acid sequence, which contain a sorting signal**

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12
Q

What does a sorting signal do?

A

A sorting signal directs the protein to the organelle in which it is required.

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13
Q

What happens when a protein lacks the sorting signal?

A

Proteins that lacks such a signal remain as permanent residents in the cytosol.

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14
Q

DNA -> DNA is what?

A

Duplication before division.

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15
Q

What is the endoplasmic reticulum responsible for?

A

Synthesis of most lipids and synthesis of proteins for distribution to many organelles. Connected with the nucleus through the outer membrane.

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16
Q

What is the golgi apparatus responsible for?

A

Protein modification (glycosylation), sorting and packaging of proteins and lipids for either secretion or delivery to another organelle.

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17
Q

What is the endosome responsible for?

A

Sort ingested molecules from endocytosis (recycle or destroy). Endocytosis is the process by which cells take in materials through the invagination of the plasma membrane (engulfing process).

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18
Q

What is the lysosome responsible for?

A

Intracellular degradation, multiple degradative enzyme and low pH (digestive system of the cell)

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19
Q

What is the peroxisome responsible for?

A

Oxidation of toxic molecules.

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20
Q

What is the mitochondria responsible for?

A

ATP synthesis by oxidative phosphorylation. Energy factory!

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21
Q

Are organelle membranes permeable or impermeable to proteins?

A

Organelle membranes are impermeable proteins.

22
Q

Organelle membranes are impermeable to proteins. So, how are proteins transported across membranes? (3 steps)

A
  1. Pores: Proteins moving from the cytosol into the nucleus are transported through the nuclear pores. The pores function as selective gates.
  2. Protein translocators (carriers): Proteins moving from the cytosol into ER and mitochondria.
  3. Vesicles: Proteins moving from one compartment to another are transported by vesicles, which pinch off from the membrane of one compartment and the fuses with the membrane of a second compartment.
23
Q

What is the main feature that distinguishes eukaryotic from prokaryotic cells?

A

The nucleus

24
Q

List the main roles of the nucleus:

A

It houses the genome, and thus is the repository of genetic information and the cell’s control center.
Separation of the genome from the site of mRNA translation

25
Q

Describe the nuclear envelope.

A

Allows control through regulation of post-transcriptional regulation and transport of mRNAs out of the nucleus.

26
Q
  1. What does the nuclear envelope separate?
  2. What two membranes does the nuclear envelope have? What do those two membranes consist of?
  3. What does the nuclear envelope do?
  4. What is the nuclear envelope permeable to?
A
  1. Separates the nuclear contents from the cytoplasm.
  2. Outer and inner membranes that consist of phospholipids.
  3. It controls traffic of proteins and RNAs through nuclear pore complexes and plays a critical role in regulating gene expression.
  4. Just like the other membranes, it is permeable to small nonpolar molecules.
27
Q

Describe the outer membrane of the nuclear envelope.

A

The outer membrane is continuous with the ER, so the perinuclear space is directly connected with the lumen of the ER.

28
Q

The inner and outer membranes of the nuclear envelope are joined by what?

A

Nuclear pore complexes.

29
Q

What are nuclear pore complexes of the nuclear envelope?

A

Are the sole channels through which small molecules pass through the nuclear envelope.

30
Q

What does the nuclear lamina (of the nuclear envelope) provide to the nucleus? What is the lamina associated with?

A

A fibrous protein mesh that provides structural support to the nucleus (makes it round). Lamina is associated with the chromatin.

31
Q

What is the nuclear lamina composed of?

A

Composed of 60-80 kilodalton (MW) fibrous proteins called lamins.

32
Q

What are lamins?

A

Lamins are a class of intermediate filament proteins that associate to form higher order structures.

33
Q

When two lamins interact, what does it form?

A

Two lamins interact to form a dimer: the alpha-helical regions wind around each other to form a coiled-coil.

34
Q

The lamin dimers associate with each other to form?

A

Lamina

35
Q
  1. What membrane are lamins associated with?
  2. Lamins are associated with this membrane via what?
A
  1. Inner membrane
  2. Via post-translational addition of lipids.
36
Q

The inner nuclear membrane contains several __________ proteins that interact with nuclear lamins:

A

Integral ;
Emerin, Lamin B receptor (LBR), and SUN proteins

37
Q

Describe what the SUN proteins do (what they bind and in what membrane, and what that makes & connects).

A

SUN proteins bind the KASH proteins in the outer membrane, making up the LINC complex that connects the nuclear lamina with the cytoskeleton.

38
Q

When mutations in the lamin occur, what is the disease that results?

A

Muscular Dystrophy

39
Q

Mutations in lamin genes cause several inherited __________ diseases.

A

Tissue-specific

40
Q

What parts of the body become stiff in muscular dystrophy? Often, what happens to the heart?

A

Elbows, neck, and heels of affected individuals become stiff. Often, there is a conduction block in the heart.

41
Q

At first, scientists thought that lamin mutations would cause what?
What are the two hypotheses now?

A

Would cause general nuclear structure defects and problems with cell division, but no.
2 hypotheses - 1) cause weak links to cytoskeleton. 2) defective chromatin localization = changes in gene transcription.

42
Q

What is the size of nuclear pore complexes?

A

They are large; diameter of 120nm and molecular mass of 125 million daltons.

43
Q

What are nuclear pores?

A

Channels through which small molecules, ions, proteins and RNA travel between nucleus and cytosol. RNAs synthesized in the nucleus must be exported to the cytoplasm for protein synthesis. Proteins (e.g. transcription factors) must be transported into the nucleus.

44
Q

There are two ways that molecules pass between the nucleus and cytoplasm. What are they? Describe these processes.

A

Passive diffusion and selective transport.
Passive diffusion: small molecules pass freely in either direction
Selective transport: Proteins and RNAs are selectively transported; requires energy

45
Q

Proteins needed for nuclear functions (e.g. RNA polymerase, histones, TFs) must be imported from…?

A

From synthesis sites in the cytoplasm (to the nucleus).

46
Q

RNAs synthesized in the nucleus must be exported to…?

A

The cytoplasm for protein synthesis (from the nucleus –> to the cytoplasm)

47
Q

What structure is critical for the physiology of all eukaryotic cells by controlling traffic?

A

The nuclear pore complex.

48
Q

Describe the nuclear pore complex.

A

Made up of 30 different proteins called nucleoporins (or NUPs). It is 30 times the size of a ribosome.
There are 8 spoke shaped proteins connected to rings at nuclear and cytoplasmic surfaces.
The spoke-ring surrounds the central channel.
The protein filaments extended from the rings are basketlike structures on the nuclear side. Cytoplasmic filaments on the cytoplasmic side (they interact w/ proteins).
FG-NUPs proteins are in the central channel and provide traffic control.

49
Q

Proteins that must enter the nucleus have amino acid sequences called…?

A

nuclear localization signals (NLS).

50
Q

What are nuclear localization signals (NLS)?
What recognizes them?

A

Are often short sequences of basic amino acids (e.g. lysine and arginine).
Are recognized by nuclear transport receptors called importins, which carry proteins through the nuclear pore complex.

Cell Biology (33 decks)

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