Theme 2 module 4

Question 1

human proteome

Answer 1

full number of proteins expressed by all herediatry information in our DNA

Question 2

genome

Answer 2

20-25,000 protein encoding genes identifies to contribute to over a million proteins encoded by our genome
single genes can encode multiple proteins

Question 3

Defining characteristics of eukaryotes

Answer 3

segregation of genetic information inside double membraned nuclear envelope
Transcription of DNA into RNA and RNA processing occurs in the nucleus

Question 4

double membrane of nucleus…

Answer 4

-is continuous and evolved from membranous network of the single-membrane endoplasmic reticulum
compartmentalization allows for a more intricate control in regulation of cellular processes

Question 5

The composition of our proteome can change…

Answer 5

in response to various factors
include an organism’s developmental stage and in response in internal and external signals

Question 6

cells are able to detect changes in their environment in numerous ways…

Answer 6

changes serve as stimuli which will result in important cellular responses

Question 7

What occurs in your body following a meal

Answer 7

cells will be sensitive and respond to this stimulus
which can include an increase in blood glucose levels
regulation comes about due to sensory responses in specialized beta islet cells of the pancreas that will leads to a cascade of events that can return measure blood glucose back to normal levels
the pancreas will modulate the synthesis and secretion of an increased amount of its own signal, a protein called insulin

Question 8

Insulin

Answer 8

an effector protein produced by pancreatic beta cells which is able to communicate with and produce a response on target cells and therefore lead to a decrease in blood glucose levels
process from stimulus to a cellular response during this cascade of events is highly regulated and is dependent on the action of important proteins and cell to cell communication

Question 9

Glucose absorption

Answer 9

glucose absorbed into bloodstream
some glucose absorption occurs in mouth across thin epithelial surfaces intimately associated with underlying blood vessels/capillaries, a large amount of glucose absorption occurs in microvilli cells of small intestine

Question 10

microvilli cells..

Answer 10

of small intestines are also intimately associated with very small blood vessels
microvilli absorb the glucose which is found in intestinal tract and then absorbed glucose molecules are transported into blood vessels
and then travel through circulatory system
after a meal the specialized pancreatic beta cells are able to detect an increase in blood glucose levels and adjust the amount of synthesis and secretion of the insulin protein and will act as an effector to reduce blood glucose

Question 11

Insulin biosynthesis

Answer 11

regulated at both transcriptional and translational levels
glucose metabolism is an important physiological event which leads to an increase in insulin gene transcription and mRNA translation
-dense rough endoplasmic reticulum can be found within a beta cell of the pancreas
because insulin is secreted from the cells the dense rough er insulin is produced

Question 12

Insulin structurally

Answer 12

translated polypeptide which is coded in the insulin gene is 110 amino acids in length
functional insulin secreted from pancreas is 51 amino acids
dorothy hodgkin was able to determine the structure of the functional insulin protein is made up of two amino acid chains
alpha chain which is 21 and a beta which is 30
two amino acid chains form a dimer which makes up the functional insulin protein
the processing of the insulin protein from a single polypeptide of 110 amino acids to a protein of 2 polypeptides of 21 and 30 amino acids is achieved by post translational modifications

Question 12

preproinsulin

Answer 12

insulin gene encodes a 110 amino acid precursor of mature insulin protein
contains an N terminal signal sequence which interacts with signal recognition particles (SRP) to facilitate translocation of preproinsulin into the lumen of the rough ER
initially processed through cleavage of signal and results in a proinsulin moleucule

Question 12

Proinsulin is..

Answer 12

further modified by other post translational modifications to obtain the mature insulin protein that is secreted from pancreatic beta cells
will undergo folding in addition to the formation of three disulphide bonds
requires assistance of chaperone proteins found within the rough ER
folded proinsulin is then transported from rough ER to golgi apparatus where further cleavage occurs and forms the mature insulin dimer with both A and B chains and releases a small C chain
only when these modifications occur can the n terminal and c terminal amino acid residues in A and B chains bind to the insulin receptors on target cells

Question 12

phosphorylation

Answer 12

reversible post translational modification which involves covalent attachment of a phosphate group to serine, threonine or tyrosine amino acid residues in a protein by enzymes called kinases

Question 12

post translational modifications

Answer 12

increase functional diversity of proteome

Question 13

Aside from cleavage, folding and disulphide bridge formation…

Answer 13

covalent attachment of other molecules and degradation of entire proteins
covalent attachments include phosphorylation, methylation and acetylation

Question 13

methylation

Answer 13

covalent addition of a methyl group

Question 14

acetylation

Answer 14

addition of acetyl group to a specific amino acid residue

Question 15

once pancreatic beta cells release insulin in response to increases in blood glucose levels…

Answer 15

these insulin effector molecules will bind to receptors expressed on specific target tissues

Question 16

Receptors

Answer 16

important proteins which receive and interpret information from signalling molecules like insulin

Question 17

there are thousands..

Answer 17

of different types of cell receptors with their ability to bind to specific signals and produce a response

Question 18

insulin protein binds

Answer 18

to a specific insulin receptor called receptor kinases
binding enables many cells to transport glucose across plasma membrane and into the cytosol of the cell

Question 19

Receptor kinases

Answer 19

exist in monomeric forms
when a signal such as insulin binds to each receptor monomer on the extracellular surface, a conformational change causes the receptor monomers to pair up (dimerize)
leads to activation of cytoplasmic domains of the receptor which have the ability to act like kinase proteins
able to engage in phosphorylation of specific amino acids
cytoplasmically situated receptor kinase domains phosphorylate each other at many regions on the receptor tails and can lead to the binding and activation of other cytoplasmic proteins

Question 20

As a result of intracellular signal amplification...

Answer 20

the extracellular insulin signal causes a series of cytoplasmic proteins to become sequentially activated and will lead to an intracellular response signal ultimately leads to the activation of glucose transporter proteins at the cell surface and the absorption of glucose

Question 21

Once insulin has bound to its receptor...

Answer 21

the conformational changes and autophosphorylation of the receptor followed by activation of other cytoplasmic proteins induces intracellular signals through the activation of a series of diverse transducer and amplifier proteins that are downstream from the activated receptor

Question 22

the initiation and maintenance of a signal is...

Answer 22

regulated by positive-feedback loops to keep the signal and amplification on

Question 23

But many elements in a signaling pathway can also activate

Answer 23

negative- feedback loops which can lead to intracellular signal termination An important feature of intracellular signaling also nvolves double-negative feedback, where an inhibitor of the signal can also be inhibited. This provides fine control in a cell in response to an extracellular signal

Question 24

Many tissues that have insulin receptor kinases are...

Answer 24

able to detect changes in the blood glucose levels and can contribute to the absorption of glucose from the blood

Question 25

The fat cells..

Answer 25

in adipose tissue will take up glucose and fatty acids and store the excess as fats in the form of triglycerides

Question 26

The liver and muscle cells...

Answer 26

are able to take up glucose from the blood and store the excess as glycogen

Question 27

However, some tissues are more efficient at absorbing glucose relative to others such as...

Answer 27

skeletal muscles are able to absorb glucose more efficiently than liver cells

Question 28

By regulating RNA processing, eukaryotes, are able to produce more than one mRNA transcript from a single gene...

Answer 28

single gene to encode for more than one protein product, and thus contributes to our proteomic complexity

Question 29

During alternative splicing, some exons may be excluded during the splicing process (being removed much like the introns)

Answer 29

leading to the production of many isoforms or different types of mature mRNA from the same pre-mRNA transcript This occurs because what the spliceosome will sometimes recognize as an exon in some primary transcripts, can sometimes be identified as an intron in other primary transcripts sometimes produces in same cell or in different types

Question 30

Example of alternative splicing is in human insulin receptor

Answer 30

The insulin receptor gene has 22 exons. In skeletal muscle cells, exon 11 is removed from the mature mRNA product (along with the transcript introns) during the splicing process. This mRNA isoform of the insulin receptor will then be translated into a higher affinity version of the insulin receptor in muscle cells. These skeletal muscle cells will then be able to mount a higher response of glucose uptake in response to an insulin signal. This is an ideal insulin receptor isoform to have at skeletal muscles, since while they contribute to lowering blood glucose levels, they also allow the muscle cells to absorb enough glucose to meet their high energy needs. In contrast, liver cells produce an insulin receptor with lower affinity to insulin. The difference lies in one key difference. During the splicing of the pre-mRNA to mature mRNA in liver cells, exon 11 is retained in the mature mRNA molecule. As a result, we see that while the message in the DNA blueprint is the same, alternative splicing leads to the processing of multiple different mRNA molecules and eventually, the translation of alternate protein isoforms

Question 31

Once the high glucose stimulus is detected by the sensor cells of the pancreas

Answer 31

insulin acts as an effector signal which targets cells of the body to absorb glucose from the bloodstream. This signal to increase glucose absorption into various cell and tissue types is also regulated. Once blood glucose levels are returned to resting levels, there will be feedback to bring the entire system back to the starting or resting point. In this case, we will see a negative feedback loop wherein the drop in blood glucose will be detected by the pancreatic cells and there will be a decrease in the secretion of insulin. As a result, the feedback of this information to the sensor cells limits any further response in the entire system.

Question 32

slide

Answer 32

The proteome is not nearly as uniform as the genome would predict it to be. While the genome is made up of four nucleotides and these nucleotides are identical in all of our cells, we have structurally and functionally mature proteins that come in different forms (or isoforms). It is the diversity of cellular proteins which contribute to the vast complexity and interactions that underlies various cellular processes. For this reason, any change to alternative splicing mechanisms, or even post-translational modifications of many cellular proteins can lead to detrimental cellular effects. For example, if the insulin protein were not processed correctly following translation, there may not be any ability for this protein to bind to the insulin receptors on target tissues. As we have seen, the insulin receptor is encoded by a single gene, in which alternate splicing results in one of two isoforms. If the insulin receptor isoform was incorrectly spliced during mRNA processing, there also would be no ability to activate glucose transport proteins that allow for the import of glucose from the blood stream at these target regions. A defect in either the insulin protein or the insulin receptor can lead to the inability to take up glucose, resulting in hyperglycemia and eventually diabetes. This is a fine example as to how the complex proteome can vary due to different patterns of gene expression and protein modification, and that these processes contribute to the role that proteins serve as functional molecules of the cell.