Hfr cell

• When F-plasmid (sex factor) integrated with chromosomal DNA then such bacteria is known as high frequency recombination (Hfr) bacteria.
• In the cross (conjugation) between Hfr cell and F- cell, frequency of recombination is very high but frequency of transfer of whole F-factor is very low.
• Hfr cell acts as donor while F- cell acts as recipient.
• At first F-factor makes sex pilus that joins donor and recipient cell then F- factor opens as replication origin then one strand is cut down. Now the 5’ end of this strand enters into recipient cell through conjugation tube.
• Since, replication origin lies somewhere in the middle of F- factor, portion of F-factor that lies at 5’ end enters first into recipient cell but the portion situated at 3’ end enters only when whole chromosomal DNA enters into the recipient cell.
• To transfer whole chromosomal DNA, it takes 100 minutes in E. coli. In most of the cases, sex pilus (conjugation tube) breaks before transfer of whole chromosomal DNA takes place. So, frequency of transfer of whole F-factor is very low. After the cross between Hfr cell and F- cell, recipient cell remains recipient.
• In this conjugation, chromosomal DNA is always almost transfer from donor to recipient cell together with portion of F- factor. So, frequency of recombination is high.

F –prime (F’) cell:

• Bacteria in which contains F-factor and a part of chromosomal DNA integrated in it is known as F-prime bacteria.
  F’ cells are formed from Hfr cell during induction of F- factor from chromosomal DNA in which F-factor carries a portion of chromosomal DNA along with it.
• In the cross (conjugation) between F-prime (F’) cell and F- cell, frequency of recombination is high as well as frequency of transfer of whole F-factor is also high.

High frequency recombination (Hfr) cell conjugation and F-prime (F’) cell

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• Mixed gland (both endocrine and exocrine function)

Structure:

• Pancreas is elongated 12-15 cm long organ consisting of head, body and tail. It is located posterior to stomach with its head in the curve of duodenum. The body and tail extends laterally. The tail touches the spleen.
• pancreas is considered as mixed gland as it acts as exocrine and endocrine gland.
• As exocrine gland, pancreas secretes digestive enzymes into pancreatic duct.
• As endocrine gland,it secretes hormones into blood.
• Only about 1% of total weight of gland acts as endocrine gland. This portion of pancreas is known as Islet of Langerhans.
• Adult pancreas contsins 200,000-20,00,000 islet of Langerhans.

Endocrine portion of pancreas is called Islet of Langerhans, which is a group of cells.

• Alpha cell= produce glucagon. Glucagon plays an important role in blood glucose regulation; low blood glucose levels stimulate its release.
• Beta cell= produce Insulin. Elevated blood glucose levels stimulate the release of insulin.
• Delta cell= produce peptide hormone Somatostatin. Pancreatic somatostatin inhibits the release of both glucagon and insulin.
• * somatostatin is also released by the hypothalamus (as GHIH), and the stomach and intestines
• F cell (PP cell)= produce pancreatic polypeptide hormone.

Hormones of pancreas

1. Glucagon

• Alpha cells produce, stores and secretes glucagon.
• Glucagon stimulate glycogenolysis and gluconeogenesis; increase blood glucose level

2. Insulin

• Beta cell produce, store and secretes insulin.
• Insulin stimulate glycogenesis; decrease blood glucose level and Store glucose in the form of glycogen in liver and muscles
• Insulin function opposite to glucagon and work to maintain normal glucose level in blood.

disorders

i. Diabetes mellitus: condition caused by destruction or dysfunction of the beta cells of the pancreas or cellular resistance to insulin that results in abnormally high blood glucose levels.

ii. hyperglycemia: abnormally high blood glucose levels

iii. hypoglycemia; abnormally low blood glucose levels.

3. Somatostatin

• inhibit release of both glucagon and insulin

Pancreas: structure, hormones and functions

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