Week 3 QFL

Explain why oxidation of protein residues may act as a marker or 'tag' for protein degradation. (hint: free radicals)

Oxygen free radicals can cause considerable damage to proteins by oxidizing particular residues on the external surface of the protein. Consequently, the protein would be unable to function properly and would need to be removed (degraded) by the cell. Thus oxidation itself is a useful marker or 'tag' for the cell to degrade a non-functional or damaged protein.

Does the conformation of a protein change as it is transported through the nuclear pore by importin?

the conformation of the imported protein probably doesn't change but the conformation of importin may change upon binding by GTP-Ran. GTP-Ran is a protein that helps to dissociate the imported protein-importin complex.

Posttranslational glycosylation of proteins is inhibited specifically by:

tunicamycin

Proteasomes seem to be comprised of the following types of subunits:

two regulatory 'particles' and one core 'particle'

In constitutive secretion:

vesicles from the trans Golgi network are sent to the cell surface for immediate secretion

In regulated secretion:

vesicles from the trans Golgi network remain in the cytosol and will not be secreted through the plasma membrane until a specific signal is received

The 26S proteasome has a:

20S core containing about six proteases

Clatherin coated pits are principally:

Aggregates of protein heavy and light chains

What kind of molecule is a SNARE, what general types are there, and what is its function?

A SNARE is a membrane bound receptor protein required for receptor-mediated membrane fusion. The acronym is for: Synaptosome associated protein receptors There are two types of SNARES: vSNARES and tSNARES The vSNARES are on the outer surface of a vesicle (v) and the tSNARES are on the target membrane (t). The interaction of v and t SNARES instigate the membrane fusion event between the vesicle membrane and the target membrane. The membrane fusion process consists of three general steps: tethering (which also involved Rab protein and tethering protein), docking (recognition between v-SNARE and t-SNARE), and fusion (membranes fused together).

Explain what a proteasome is, what it does, and how it achieves its affect.

A proteasome is a large multi function, multi-enzyme, multi protein complex comprised of a core particle flanked by two regulatory particles. The proteins are fed through the regulatory cap where they unfold and feed through the core of the proteasome. In the core they are degraded into short peptides by proteases. The short peptides are bound by MHC1 proteins that present them on the extracellular surface of the cell where they are subsequently detected by CD8-positive T cells

The 26S proteasome complex is comprised of the following:

C. One 20S core and two 19S subunits

It is important to eliminate misfolded proteins because they may result in:

Creutzfeldt-Jakob disease Alzheimer's Disease Prion Disease Huntingtons Disease

Explain why degradation of a cyclin protein would be necessary to a cell

Cyclin proteins controls the cell cycle phases and determine the progress of a cell during the mitosis phase. Cyclin's only act at particular times during a cell cycle and so must be disposed of when not needed. If cyclins were not eliminated then this would confuse the organization and control of the cell. This would fatally affect the cell.

The half life of a protein is:

D. the time taken for half of the [protein] to degrade

Targeted protein degradation may involve:

D. ubiquitination, metal-catalysed oxidations, PEST sequences, or specific N-terminal residues

Protein targeting is the process of:

Directing proteins to particular cellular or extracellular locations

If a protein was found to have a half-life of about one week what inference could you make about this protein?

It is a relatively long lived protein that may have a structural role because most structural proteins have a half life from days to months whereas short lived proteins from minutes to hours are temporary extracellular or regulatory proteins.

PS341 is a drug that has been seen to be very effective at treating multiple myeloma in some patients. This drug seems to target:

The proteosome degradation system

Which of the following is true about the sorting pathway for proteins destined for incorporation into lysosomes or the plasma membrane of eukaryotic cells?

The signal recognition particle (SRP) binds to the signal peptide soon after it appears outside the ribosome.

Which of the following best describes the requirements for the movement of proteins into the mitochondria.

a signal sequence

Targeting a protein to the nucleus differs from targeting a protein to the endoplasmic reticulum in the following way:

a signal sequence is used which can be anywhere in the protein sequence

The importance of protein degradation in normal metabolism is evident in:

cyclin proteins in cell cycle regulation regulation of transcription factors signal transduction pathways removal of mutated proteins

The function of the 26S proteasome is to:

degrade proteins into peptides containing 5 to 25 residues provide peptides that can be used by MHC class I receptors

Three interelated mechanisms used in targeting proteins are:

glycosylation, signal sequence, and signal patch

Ubiquitin:

is 76 residue protein forms covalent bonds with proteins requires ATP for it action important for targeted protein degradation

Tim and Tom, with reference to protein targeting, are:

membrane proteins responsible for directing proteins into mitochondria

Directing a protein to the Golgi usually involves the following processes:

no signal sequence, O-linked glycosylation, a signal patch

The signal sequences that direct proteins to the nucleus are:

not located at the ends of the peptide, but in its interior

Read the following description and then determine both the method of protein targeting and the cellular location of the targeting. 20 to 35 amino acids long prevalence of serine, threonine, and basic residues chaperone proteins involved

signal sequence and mitochondria

Read the following description and then determine both the method of protein targeting and the cellular location of the targeting. 13 to 16 amino acids long 10 to 15 hydrophobic amino acids acts to attract the signal recognition particle (SRP)

signal sequence and the endoplasmic reticulum