Biochem Lec 16-17

Question 1

what is structural formula for all monosaccharides and what is simplest monosaccharide

Answer 1

all monosaccharide share same chemical formula of CH2O as base and simplest monosaccharide is the triose which has structural formula of CH2O and is either aldose or ketose depending on functional group attached

Question 2

how are carbons of carbohydrates numbered

Answer 2

using numbers like C-1 for carbon in carboxyl group and one after will be C-2, and so on

Question 3

what is the configuration assigned to carbohydrates

Answer 3

it is either L or D which is assigned to asymmetric and chiral carbon that is furthest away from carbonyl and knowing the number of chiral carbons, you can know the possible number of different isomeres using 2^x

Question 4

why do sugars take on ring structure and how do they configure to such structure

Answer 4

ring structures are more stable as they are lowest in energy and to go from chain to ring, aldehyde and hydroxyl groups interact

Question 5

what bonds allow for carbohydrates cyclization

Answer 5

the aldehyde and ketone carbonyl will undergo nucleophilic attack by hydroxyl groups to form either a 5-member furan ring or 6-member pyran ring
the new bond holding the ring will be either hemiacetal if it is aldehyde derivative or hemiketal if ketone derivative

Question 6

how can we detect chirality of ring strucured carbohydrates

Answer 6

there is anomeric carbon that is chiral as it cna be alpha or beta anomer and that cna be detected by mutorotation where there is change in optical rotation of polarized light
B-anomer are higher in existance, 63%, as they are more favorable due to positioning of hydroxyl group and alpha-anomers exist 36% of the time while linear structure exist 1% of the time and dueing that time it is interacting with other molecules or changing into ring structure.

Question 7

how are carbohydrates modified

Answer 7

sugars can be phosphorylated, methylated, or they can have the hydroxyl and carbonyl removed
these modifications will increase in complexity of carbohydrates structure

Question 8

Why are different positions important

Answer 8

differences in L and D cause differences in order/position of functional groups which impact the interactions

Question 9

how are carbohydrates chain made

Answer 9

by a glycosidic bond which is through a condensation reaction, so H2O is lost

Question 10

what are other types of glycosidic bonds

Answer 10

that would be intermolecular bonds formation between hydroxyl on amine and reactive anomeric carbon on other molecule and these glycoproteins may be O-linked or N-linked

Question 11

what are the monosaccharides involved in the following complex carbohydrates:
1- amylose
2- lactose
3- amylopectin
4-sucrose

Answer 11

1- two glucose attached by alpha-1,4 glycosidic bond
2- galactose and glucose attached by beta-1,4 glycosidic bond
3- amylopectin being chain of glucose attached by alpha-1,6 glycosidic bond at branch points
4- glucose bonded to fructose through alpha-1,2 glycosidic bond

Question 12

what are polysaccharides

Answer 12

they are chains of polymers important for energy storage, cellular structure, and recognition
they are also known as glycans as they can be homopolymer due to having same monosaccharide, glycogens, or a heteropolymer due to having different monosaccharide, glycoproteins

Question 13

what are characteristic of carbohydrate starch

Answer 13

can be amylose, amylopectin, and alpha amylose
amylose consist of unbranched alpha 1-4 linkages
amylopectin has linear glucose chains joined by alpha 1-4 linkages abd also alpha 1-6 linkages at branch points every 30 glucose units
alpha amylose is secreted from salivary glands and pancreas and cleaves random locations along chain to give maltose and matotriose

Question 14

what are charcteristics of cellulose taht make it unqiue

Answer 14

it is teh most abundant organic compound and serve structural role in plants but it haves unbranched chaisn of glucose linked by beta 1-4 linkages with many hydrogen bonds and cellobiose is disaccharide glucose linked by beta 1-4 linkages

Question 15

how is glycogen important and what makes it important

Answer 15

it is storage for long branched chains of glucose and contains branch points every 8-12 glucose units
it also has a dimer of glycogen at center and when glucose is needed or not, it will be added or removed from nonreducing ends

Question 16

can cells use any type of carbohydrate for fuel

Answer 16

no, cells can only use monosaccahrides as source of energy so lactase, maltase, and sucrase will help cleave associated dissacharides

Question 17

why is sugar sequencing more complicated

Answer 17

because there are many different isomeres as polysaccharides differ in composition, connectivity, and configuration while proteins were less complicated as they are made of 4 nucleotides

Question 18

glucose is important for fuel and enrgy, but how does it move and enters different parts of the body

Answer 18

through glucose transporters and since glucose is polar molecule, it cannot diffuse through lipid bilayer and these transporters also move glucose due to concentration gradient

Question 19

what are some of the key types of different glucose transporters

Answer 19

sodium glucose co-transporters are secondary active transporter so they move glucose from low to high concentration
glucose trasnporters- facilitated diffusion so move glucose from high to low concnetration, known as GLUT and GLUT 4 is insulin dependant
fructose transporters- also afcilitated diffusion

Question 20

why would someone who has diabetes type I and takes more insulin than needed end up with hypoglycemia

Answer 20

that is because GLUT 4 transporters, which are insulin dependant, will keep on moving glucose to muscle and adipose cells which will decrease glucose for other cells like RBC which causes low glucose levels in the blood and lead to hypoglycemia

Question 21

what is true about glycolysis which involves glucose and ATP

Answer 21

glucose and ATP availibilty both regulate glycolysis

Question 22

what is an overview on carbohydrate metabolism and hormone involvment

Answer 22

in anabolic state, insluin will increase glucose utilization as the glycolitic pathway is important for ATP production from simple monosaccahrides and the excess glucose will be stored as glycogen in muscle or liver cells by glycogen synthase when ATP is high
in catabolic state, epinephrine and glucagon are the hormones that signal for glycogen breakdown and lead to ATP production or releasing glucose from liver

Question 23

overview of glycolysis

Answer 23

it is a pathway highly utilized by cells requiring immediate soyrce of energy such as RBC and cells in cornea for example
it is a 10 step catabolic pathway found in cytoplasm and it starts with glucose, a 6C molecule
can be divided into two stages:
1- the preperation and consist of the first 5 steps where 2 ATP are used to prepare this glucose molecule for breakdown and generate 2 GAPs, 2 of the 3C molecules
2- consist of last steps, from 6 to 10, it is where the 2 pyruvates are produced and so will 2 NADH and 4 ATP also be reduced
so end up with 2 ATP as the net from glycolysis
then the two pyrivates gets oxidized in mitochondria and generate more NADH when oxygen is available

Question 24

how can galalactose and fructose, also monosaccahrides be used in glycolysis

Answer 24

they can be converted into intermediates of the glycolysis pathway and end up being used in same way, generate teh 2 ATP
fructose gets converted into DHAP and glyceraldehyde-3-phosphate
galactose gets converted into glucose-6-phsophate

Question 25

how can glycolysis be regulated

Answer 25

there are three steps in the glycolysis pathway that will allwo for regulating the process, that will be step 1+3+10
these three steps are irreversible

Question 26

overview on how glycolysis is regulated

Answer 26

it si regulated using teh enzymes that cleave those reactions by active site, allosteric site, or by covalent modifications
step 1= hexokinase gets inhibited by build up of its product known as glucose-6-phosphate as it binds the allosteric site and cause confomrtaional change
step 3= phosphofructokinase 1 (PFK-1) gets inhibited by amount of ATP or citrate and will be activated by AMP, ADP ir fructose-3,6-bisphosphate
step 10= where pyruvate kinase gets inhibited by phosphorylation and other allosteric regulators

Question 27

how does hexokinase end up binding and giving glucose-6-phosphate from first step of glycolysis

Answer 27

glucose gets phosphorylated using ATP by hexokinase where the ATP and gamnesium ions bind the enzyme’s lobe away from glucose’s binding site and these moelcules, ATP and magnesium, cause conformtaional change once the subtrate, glucose, bind by closing in the enzyme around glucose and then a C6 hydroxyl attack will produce glucose-6-phosphate
this step ends up trapping glucose in cell as GLUT transporters cannot bind glucose-6-phosphate and only liver cells have ability to reverse this step
by doing thise, the cell ensure that glucose gets used to generate energy by glycolysis, get stored as glycogen if in liver or muscle cell, or to end up used to make new molecules

Question 28

how is PFK-1 regulated and how does this affect glycolysis

Answer 28

PKF-1 is the enzyme ctaalyzing the third step in glycolysis and that is also teh second ATP requiring step as the PFK-1 will take phosphate group from ATP and give it to C1 hydroxyl of F-6-P
but this enzyme can also be allosterically regulated as it has two sites, the active site for F-6-P and the allosteric site which if bound by ATP/citrate will inhibit enzyme, but if bound by AMP/ADP then it activate enzyme

Question 29

significance of pyruvate kinase and its importance for last step of glycolysis

Answer 29

pyruvate kinase is last enzyme for last step of glycolysis and it is inhibited by phosphorylation as phosphorylated pyruvate enzyme can be due to having alanine/acetyl CoA/and high level of ATP, but active pyruvate kinase is one that is dephosphorylated as that means there is low ATP and high AMP and high fructose-1,6-bisphosphate

Question 30

how is glycogen synthesized

Answer 30

when ATP is high and glycolysis slows down, excess glucose gets stored as glycogen by glycogen synthase
the enzyme can only add UDP-glucose as it create new alpha 1-4 bond on the nonreducing ends of glycogen
so glucose will still get phosphorylated by hexokinase, but glucose-6-phosphate wull be isomerized by phosphoglucomutase to form glucose-1-phosphate and then another enzyme, UDP-glucose pyerophorphorylase will use ATP and activate glucose-1-phosphate and make that UDP-glucose
this pathway is activated by insulin signaling which activate glycogen synthase using dephosphorylation

Question 31

how does phosphoglucomutase reaction occur and how does metabolic state affect it

Answer 31

it will make glucose-6-phosphate from glucose , but will form an inetrmediate glucose-1,6-bisphosphate and then turn it to glucose-1-phosphate ]
this is nonenergy reaction and will go either way depending on metabolic state
will inhibit glycolyssi adn take glucose and phosphorylate it when there is insulin signallying due to being in anabolic phase

Question 32

what is the overall reaction for glycogen synthase and the free energy change of reaction

Answer 32

the process consist of two steps:
1- G1P+UTP–> UDP+PPi G= 0
2- PPi–>2Pi G= -19 UDP+Glycogen(n) –>Glycogen(n+1)+UDP
this shows how the resulting diphsosphate are two unstable so they end up breaking into 2 seperate phosphates

Question 33

what is glycogenolysis and when does it occur

Answer 33

this is during epinephrine and glucagon signalling= catabolic phase
this lead to phosphorylation and activating glycogen phosphorylase and inactivation glycogen synthase by phosphorylation as well
the pathway is glycogenolysis one where there is phosphorolysis reaction by using phosphate to release the glucose-1-phosphate from nonreducing ends and theb convert it to glucose-6-phosphate by phosphoglucomutase since glucose-1-phosphate cannot be used directly