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.