Metabolism 6: Regulation of Metabolism

-

By the cell and hormones

The generation of energy produces 60% heat and 40% ATP energy. Cells regulate the entry of substances depending on their needs. The rate-limiting step in energy production is where fructose-1,6-biphosphate is produced. This molecule is involved in the regulation of metabolism, in association with an enzyme called phosphofructokinase.


Phosphofructokinase is an enzyme that adds a phosphate group onto fructose-6-phosphate molecule. This makes it the previously mentioned fructose-1,6-biposphate. It has multiple binding sites on it, specifically for ATP, ADP and citrate. The binding of ADP moves the reaction forward, although binding of ATP inhibits the process, restricting glycolysis. Citrate, a product of the Krebs cycle, also inhibits the production of fructose-1,6-biphosphate. This means that there is nearly a negative feedback mechanism to restrict the process of glycolysis.


Pyruvate dehydrogenase is another enzyme that controls the rate of progression of these reactions. NADH inhibits the activity of pyruvate dehydrogenase.

Comments

Post a Comment

Popular posts from this blog

Growth and Development 2: Placentation and Hormones

-
How does the placenta form? The placenta forms from the embryonic trophoblastic/mesoderm tissues, as well as the maternal endometrial tissues. Vessels develop in the embryonic tissues which then supply nutrients to the foetus from the maternal blood supply. The chorion develops fingerlike villi which have become vascularised and extend to the embryo as umbilical arteries and veins. The embryo, amnion and yolk sac float in a fluid-filled chamber attached to the placenta by a body stalk. The placenta grows and begins to develop into organised regions, bulging into the uterine cavity as it grows. It becomes fully developed by the end of the third month (end of first trimester), where the foetus moves farther from the placenta connected by the umbilical cord. By 12 weeks, the placenta is providing nutrients and removing wastes, meaning it takes on the role of oestrogen and progesterone which used to be released from the corpus luteum. Decidua capsularis: endometrium surroundi...
Read more

Growth and Development 4: Labour, foetal circulation and lactation

-
What happens when we give birth? During the last week of pregnancy, oestrogen reaches a peak. This causes myometrial weakness and irritability. Then, weak 'Braxton Hicks' contractions occur, which become uterine contractions stimulated by oxytocin and prostaglandins closer to birth. Emotional and physical stress establishes a positive feedback mechanism with the hypothalamus, increasing oxytocin release. The stages of labour are summarised below:   1.   Dilation Stage (8 hours) Onset of labour Cervix dilates Foetus moves towards birth canal Contractions begin and increase in frequency Water eventually breaks   2.    Expulsion Stage (2-3 hours) Cervix pushed open by foetus Contractions increase in intensity, frequency and length Continues until foetus emerges from vagina (delivery) Surgical intervention possible: episiotomy (cutting of perineal membrane) or caesarean section Newborn health assessed immediately   3.   Plac...
Read more

Lymphatics and Immunity 3: Cell-Mediated Immunity

-
Image
What is adaptive immunity then? Adaptive or specific immunity responds to specific antigens through the coordinated action of T and B cells. It is only developed after birth. Adaptive immunity involves both cell-mediated and antibody-mediated immunity. Cytotoxic T cells provide cell-mediated immunity, providing defence against abnormal cells and pathogens inside  cells. B cells provide antibody-mediated immunity, providing defence against antigens and pathogens in body fluids. There are four properties of immunity: Specificity - response to only a specific type of antigen Versatility - production of many types of lymphocytes Memory - active lymphocytes stay in circulation and provide immunity against new exposure Tolerance - immune system ignores normal antigens What is cell-mediated immunity? T cells only recognise antigens that are bound to glycoproteins in a plasma membrane. These are termed major histocompatibility complex proteins. These proteins differ betwee...
Read more