Unit 6 Regulation (12-16%)

Negative Feedback mechanisms

maintain dynamic homeostasis for a particular condition by regulating physiological processes, returning the changing condition back to its original set point (regulation of body temp)

Positive Feedback mechanisms

amplify responses and processes in biological organisms. The condition initiating the response is moved farther away from the initial set-point. Amplification occurs when the stimulus is further activated which, in turn, imitates an additional response that produces system change.

Cell-to-cell Communication

cells receive or send inhibitory or stimulatory signals from other cells, organisms, or the environment. Single celled → response to environment, multicellular → signal transduction pathways coordinate the activities within individual cells (ex. Epinephrine stimulation of glycogen breakdown in mammals)

Cells communicate by cell-to-cell contact

Immune and plant cells interact by cell-to-cell contact → antigen-presenting cells, helped T-cells and Killer T-cells, or plasmodesmata between plants cells allow material to be transported from cell to cell.

Cells communicate over short-distances

by using local regulators that target cells in the vicinity of the emitting cell. (ex. Neurotransmitters, plant immune response)

Signals released by one cell can

travel long distances to target cells of another cell type (ex. Hormones)

A receptor protein

recognized signal molecules, casuing the receptor protein’s shape to change, which initates transduction of the signal (Ex. G-Protein linked receptors, ligand gated ion-channels, tyrosine kinase receptors)

Signal Transduction is

process by which a signal is converted to a cellular response. Signaling cascades relay signals from receptors to cell targets, often amplifying the incoming signals, with the result of appropriate responses by the cell

Second Messengers are

inside of cells and often essential to the function of the cascade

Signal Transduction pathways include

Protein modifications or phosphorylation cascades in which a series of protein kinases add a phosphate group to the next protein in the cascade sequence.

Gene Regulation in Prokaryotes

(1) Inducers (turn genes on) and repressors (turn genes off) are small molecules that interact with regulatory proteins and/or regulatory sequences

(2) regulatory proteins inhibit gene expression by binding to DNA and blocking transcription (negative control)

(3) regulatory proteins stimulate gene expression by binding to DNA and stimulating transcription (positive control) or binding to repressors to inactive repressor function

Gene Regulation in Eukaryotes

(1) Transcription factors bind to DNA sequences and other regulatory proteins

(2) Some of these transcription factors are activators (increase expression), while others are repressors (decrease expression)

(3) The combination of transcription factors binding to the regulatory regions at any one time determines how much, if any, of the gene product will be produced.

Immunity

Plants, invertebrates and vertebrates have multiple, nonspecific immune responses (ex: phagocytes engulf and digest pathogens with the help of lysosomes)

Mammals use specific immune responses triggers by a natural or artificial agents that disrupt dynamic homeostasis

Mammalian Immune System

Cell mediated → cytotoxic T cells, a type of lymphocytic white blood cell, target intracellular pathogens when antigens are displayed on the outside of the cells

Humoral → B cells, a type of lymphocytic white blood cell, produces antibodies against specific antigens

Antigens are

recognized by antibodies to the antigen

Antibodies are

proteins produced by B cells, and each antibody is specific to a particular antigen. A second exposure to an antigen results in a more rapid and stronger immune response.

Virus Replication

Viruses inject DNA or RNA into host cell, highly efficient replicative capabilities that allow for repaid evolution, replicate via lytic cycle allowing one virus to produce many progeny, allows for mutations to occur through host pathways. Some can integrate into host DNA and est a latent infection.

RNA viruses

lack replication error-checking mechanisms, thus have higher rates of mutation

Antibody

A protein produced by B-cells that binds to a specific antigen to help destroy it.

Antigen

A molecule (often on a pathogen) that triggers an immune response.

B-cell

A type of white blood cell that makes antibodies for specific antigens (part of humoral immunity)

Cell-mediated Immunity Communication

Immune response where T-cells directly attack infected or abnormal cells.

Cyclic AMP (cAMP)

A second messenger molecule that relays signals inside the cell, often activating other proteins.

Cytotoxic T-cell

A T-cell that kills infected cells or cancer cells by releasing toxic substances

G-protein Linked Receptor

A cell surface receptor that activates a G-protein, which then triggers a signal inside the cell

Helper T-cell

A T-cell that activates B-cells, cytotoxic T-cells, and other immune cells by releasing signaling molecules

Hormone

A chemical messenger that travels through the bloodstream to target organs and regulate body functions.

Humoral Immunity

Immunity involving B-cells and the production of antibodies that circulate in blood and lymph

Inducer

A molecule that triggers gene expression, often by inactivating a repressor

Lytic Cycle

A viral life cycle where the virus immediately replicates in a host cell and causes it to burst (lyse).

Lysogenic Cycle

A viral life cycle where viral DNA integrates into the host genome and replicates along with it without immediately killing the host

Negative Feedback

A process where a change in a system causes a response that counteracts that change (returns system to stability)

Operon

A cluster of genes in prokaryotes controlled by a single promoter and operator

Operator

A DNA segment where a repressor can bind to block transcription

Phagocyte

A white blood cell that engulfs and digests pathogens and debris.

Phagocytosis

The process by which a cell engulfs large particles like pathogens

Phosphorylation Cascade

A sequence of events where one enzyme phosphorylates another, amplifying a signal inside the cell

Positive Feedback

A process where a change in a system causes a response that amplifies the original change

Protein Kinase

An enzyme that adds phosphate groups to proteins, often activating or deactivating them.

Receptor

A protein on the surface or inside a cell that binds to a specific molecule (like a hormone or neurotransmitter) to trigger a response

Repressor

A protein that binds to an operator to prevent gene transcription

Retrovirus

A virus that uses RNA as its genetic material and copies it into DNA using reverse transcriptase.

Reverse Transcriptase

An enzyme used by retroviruses to make DNA from their RNA genome

Second Messenger

Small molecules inside cells that help amplify and distribute a signal from a receptor (like cAMP)

Signal Cascade

A series of biochemical reactions inside a cell that amplify and carry a signal from a receptor to a target

Signal Transduction

The process of converting an external signal into a functional change inside the cell

Signal Transduction Pathway

A series of steps (involving proteins and second messengers) that transmit and amplify signals inside a cell

Transcription Factor

A protein that binds to DNA and regulates gene expression by promoting or blocking transcriptior

Virus

A nonliving infectious agent made of genetic material (DNA or RNA) inside a protein coat

White Blood Cell

Immune system cells that defend the body against infections and foreign substances