Bio/Biochem Flashcards
Explain the mechanism of ADH and its effect on osmolarity of the ascending limb of the Loop of Henle.
When a person becomes dehydrated, the brain secretes ADH (Vasopressin), which increases water reabsorption at the collecting ducts. Reabsorption occurs through pores (aquaporin proteins) that are opened up in the collecting ducts, allowing water to pass into the medulla.
As a result, there will be more water in the medulla. A more dilute medulla shifts the equilibrium between the filtrate in the ascending limb and the medulla, driving more ions out of the ascending limb (Note: recall that the ascending limb is impermeable to water, but highly permeable to ions). This increased removal of ions decreases the osmolarity of the filtrate in the ascending limb.
Which type of polysaccharides cannot be digested by humans?
Humans cannot digest β-linked saccharides; vertebrates can only digest α-linked saccharides using their own enzymes.
However, an important exception to this rule is that lactose, which has β-linked saccharides, and it can be digested. Nearly all human babies produce the enzyme lactase. However, only a certain percentage of individuals continue to express lactase in adulthood. The presence, absence, or deficiency of lactase enzyme in adults is responsible for the various degrees of lactose intolerance.
How do you elute bound proteins from the column in anion exchange chromatography column?
In ion exchange, the column is either positively or negatively charged, and molecules bind if they are of the opposite charge. To elute the molecules, you add a high concentration of an ion of the opposite charge to outcompete the bound molecules and elute them off.
What type of stereochemical relationship do D- and L- sugars have with each other?
D and L sugars are mirror images of one another, making them enantiomers.
Diastereomers are stereoisomers that are not enantionmers.
Explain the differences between gram-positive and gram-negative bacteria.
Bacteria are separated into Gram positive and Gram negative classes based on how they respond to Gram staining.
Both Gram positive and negative bacteria contain peptidoglycan in their cell wall, but only Gram negative bacteria have both an inner and an outer membrane. Also, Gram negative bacteria are the only class that contains lipopolysaccharides.
Explain the mechanism of Calcitonin and Parathyroid hormone (PTH)
Calcitonin (CT) transiently inhibits osteoclasts without affecting osteoblasts or bone deposition, thus allowing some bone turnover while shifting the balance toward bone building.
CT is produced naturally in the thyroid in response to high blood calcium. It has the net effect of lowering blood calcium levels, in contrast to the effect of parathyroid hormone (PTH), which increases blood calcium through the indirect stimulation of osteoclasts.
They are both regulated by blood calcium levels therefore their physiological effects are best described as a negative correlation since they have opposite effects on blood calcium levels.
What function do ribosomes bound to the Rough ER perform?
Ribosomes bound to the rough endoplasmic reticulum in eukaryotic cells synthesize hydrolytic enzymes that function in the lysosomes, or proteins that are secreted by the cell (AKA secretory proteins).
Remember, prokaryotic and eukaryotic ribosomes are not identical in structure. Eukaryotic ribosomes have a sedimentation coefficient of 80S, with 60S and 40S subunits. Prokaryotic ribosomes have a sedimentation coefficient of 70S, with 50S and 30S subunits.
What is a common acetylation agent found in the body?
Acetyl-CoA is commonly used by enzymes in the body for acetylation reactions as the carbonyl carbon is easily attacked by the nucleophile nitrogen of an amino acid residue.
Acetamide contains an amide linkage that is stable due to resonance and therefore unlikely to donate an acetyl group.
Acetic anhydride is an acetylating agent used in laboratory organic synthesis, but is not a natural biological molecule in vivo.
Explain the mechanism in which chyme passes through the digestive system.
Think “DJ Ilieum” (Duodenum –> Jejunum –> Ileum)
Chyme is the semi-fluid mass of partly digested food that is expelled by the stomach, through the pyloric valve (sphincter), into the duodenum (the beginning of the small intestine).
Chyme emerging from the stomach is very acidic (pH ~ 2). The duodenum secretes a hormone, cholecystokinin (CCK), which causes the gall bladder to contract, releasing alkaline bile into the duodenum. The duodenum also produces the hormone secretin to stimulate the pancreatic secretion of large amounts of sodium bicarbonate, which then raises the pH of the chyme to 7.
The chyme then moves through the jejunum and the ileum, where digestion progresses.
Explain the functions of DNA Helicase, Primase, Ligase and Polymerase
One of the DNA Polymerases involved in DNA repair removes the RNA primer and replaces the ribonucleotides with deoxyribonucleotides. Ligase then seals the gap in the sugar-phosphate backbone.
In other words, DNA polymerase removes RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3’ end of Okazaki fragments.
The function of primase is to polymerize the RNA primer so DNA polymerase can use the free 3’ OH group to begin DNA synthesis.
The function of helicase is to unwind the double stranded DNA to make to single-stranded templates for replication.
What is the difference between glycolytic fibers and oxidative fibers?
Muscles that rely exclusively on glycolysis are known as fast, glycolytic fibers. Per glucose metabolized, or per ATP produced, they will produce much more lactic acid than slow, oxidative fibers that preferentially rely on aerobic respiration.
For this reason, muscles that rely exclusively on glycolysis fatigue more quickly than muscles that utilize aerobic respiration. This provides evidence in support of a correlation between increased lactic acid (and/or the associated decrease in pH) and more rapid muscle fatigue.
What is a likely result in the dysfunction of pancreatic β-cells?
If the β-cells cannot function properly, there would be a severe lack of insulin, which would replicate the symptoms of diabetes.
Hypoglycemia on the other hand, would be the result of the dysfunction of the α-cells because they produce glucagon, but not the β-cells.
From which structure in a human cell do functional ribosomes originate?
The nucleolus of the cell serves as the site for ribosome synthesis and assembly.
Ribosomes are present on the surface of rough ER, but do not originate from there.
Explain Polymerase Chain Reaction and what two pieces of information are required.
First, one must know the length of the gene to be amplified so that the correct elongation time can be determined. Second, one must know the nucleotide sequence of the primer region in order to design forward and reverse primers. These primers must be complementary to the 3’ ends of both strands for the region being targeted.
The first step of PCR is to melt the DNA, creating two single strands. The DNA is then cooled and these primers anneal to their intended complementary nucleotide sequence. This allows DNA polymerase to copy only those segments. The polymerase will not copy other segments because it requires a primer.
