Systems Biology
Steroid hormones are classified into three groups: glucocorticoids, mineralocorticoids, and sex hormones, and they are synthesized from cholesterol carried by low-density lipoproteins (LDL). These hormones are released from cells of endocrine glands via diffusion and require carrier proteins to help them move through the bloodstream. Steroid hormones have long half-lives in the blood, allowing them to be managed after being released.
When steroid hormones are not bound to a carrier protein, they are in an active state and can affect target cells by passing through the cell membrane. Inside the target cells, steroid hormones bind to their receptors, forming a hormone receptor complex. This complex passes through the nuclear envelope and directly binds DNA to either increase or decrease the expression of genes they act on. Ultimately, this affects the amount of protein produced, leading to changes in cell function.
Lesson Outline
<li>Notable steroid hormones<ul> <li>Glucocorticoids for stress response</li> <li>Mineralocorticoids for salt and blood pressure regulation</li> <li>Sex hormones for reproduction regulation</li></li> <li>Names of steroid hormones typically end in oid, ol, or one (e.g., cortisol, estriol, pregnenolone, cortisone, aldosterone) </li></ul> <li>Steroid hormone synthesis <ul> <li>Originating from cholesterol carried by LDLs</li> <li>Cells of endocrine glands receive cholesterol</li> <li>Cholesterol is converted into steroid hormones via enzymes in mitochondria and smooth ER</li> </ul> </li> <li>Release and transport of steroid hormones <ul> <li>Diffuse across the cell membrane of endocrine gland cells</li> <li>Transported via carrier proteins in the bloodstream</li> <li>Inactive when bound to carrier proteins</li> <li>Long half-lives in the blood</li> </ul> </li> <li>Regulating active hormone levels and feedback loops <ul> <li>Concentration of carrier proteins affects action of steroid hormones</li> <li>Example: cortisol and corticosteroid binding globulin</li> </ul> </li> <li>Interaction with target cells <ul> <li>Receptors inside the target cell</li> <li>Steroid hormone can diffuse through the cell membrane</li> <li>Formation of hormone receptor complex</li> </ul> </li> <li>Impact on gene expression <ul> <li>Hormone receptor complexes bind to DNA, which can increase or decrease gene expression by altering the amount of messenger RNA</li> <li>Cell function is changed by altering protein synthesis</li> </ul> </li>
Don't stop here!
Get access to 71 more Systems Biology lessons & 8 more full MCAT courses with one subscription!
FAQs
Steroid hormones are synthesized from cholesterol through a series of enzyme-catalyzed reactions. Cholesterol is transported to the steroidogenic cells by low-density lipoproteins. Once inside the cell, cholesterol undergoes a series of modifications to produce various steroid hormones, including glucocorticoids, mineralocorticoids, and sex steroids. The specific hormone produced depends on the particular cell type and enzymes present.
Cortisol is a glucocorticoid steroid hormone that plays a critical role in metabolism, immune response, and stress adaptation. Corticosteroid binding globulin (CBG) is a transport protein that binds to cortisol and transports it in the bloodstream. CBG helps maintain a reservoir of cortisol in the blood, protects it from degradation, and ensures that only the appropriate amount of free cortisol is available to tissues at any given time. This free cortisol can then bind to specific hormone receptor complexes to regulate gene expression and protein synthesis in target cells.
Steroid hormones regulate protein synthesis by directly affecting the rate of gene transcription in target cells. When a steroid hormone binds to its specific intracellular receptor, the hormone receptor complex is formed. This complex then moves to the cell nucleus and interacts with hormone response elements (HREs) located in the promoter regions of target genes. By doing so, the hormone receptor complex modulates the recruitment of transcription machinery and coactivators, ultimately leading to the production of messenger RNA (mRNA). The mRNA is then translated by ribosomes in the cytoplasm to synthesize new proteins. This process allows steroid hormones to alter cellular function and maintain homeostasis in the body.
