Unit 1: Homestasis

DNA codes for proteins that do the majority of work in cells. Specialized cells build

tissues that work together to form systems. Human body systems maintain homeostasis

to keep us ALIVE!

What molecule is responsible for inheritance?Hershey and Chase’s Experiment

A bacteriophage is a virus that infects bacteria Made of a protein coat and DNA

Results convinced the scientific world that DNA is the hereditary material of all living things

Deoxyribonucleic AcidThe Double Helix

Studies showed that the percentages of adenine and thymine are almost always equal in DNA. The percentages of guanine and cytosine are also almost equal.

Rosalind Franklin’s X-ray diffraction studies revealed the double-helix structure of DNA.

In 1953, James Watson and Francis Crick built a model that explained the structure of DNA.

Alternating sugar-phosphate backbone

Base pairs are attached at the sugars A makes a double H-bond with T C makes a triple H-bond with G

Deoxyribonucleic Acid

Monomer = nucleotide3 Parts of a nucleotide:

1. Deoxyribose sugar2. Phosphate3. Nitrogen base

Pyrimidines (single-ring)• Thymine (T)• Cytosine (C)

Purines (double-ring)• Adenine (A)• Guanine (G)

Deoxyribonucleic AcidDNA backbones run anti-parallel to one anotherComplimentary Base Pairing Rules:Purine (double ring) with a Pyrimidine (single ring)Only A and T make Double Hydrogen BondsOnly C and G make Triple Hydrogen Bonds

One Gene- One Polypeptide Hypothesis

Genes are segments of DNA that code for specific proteins (chains of amino acids)

Proteins give us our physical and chemical traits.

Proteins perform most functions in cells

Amino AcidsMonomers of proteins20 different kinds

11 nonessential (our body can make them)

9 essential (we must obtain them in our diet)

All consist of a central carbon atom bonded to four partners Amino group Carboxyl group Hydrogen “side-chain”

The “side-chain” makes it unique

Central Carbon

Monomers of proteins20 different kinds

11 nonessential (our body can make them)

9 essential (we must obtain them in our diet)

All consist of a central carbon atom bonded to four partners Amino group Carboxyl group Hydrogen “side-chain”

The “side-chain” makes it unique

Building a Protein… form and function

Each protein has a unique sequence of amino acids (coded by DNA)

Most chains are at least 100 amino acids long

Many proteins are composed of one or more chains

Shape determines function Shape is influenced by

Surrounding environment (aqueous or not)

Temperature pH

Denaturation occurs when the protein unravels and loses its ability to function properly

The Cell Theory

All living things are composed of cells

Cells are the building blocks of more complex structures

All cells come from preexisting cells

http://learn.genetics.utah.edu/content/begin/cells/scale/

Negative Feedback Loops and Homeostasis

• Mostly commonly used feedback loop in the body.

• Used to counteract a stimulus, but not eradicate it.

Negative Feedback Loops

Human blood pressure. When blood pressure increases, signals are sent to the brain from the blood vessels. Signals are sent to the heart from the brain and heart rate slows down, thus helping blood pressure to return to normal.

Hunger. When a human is hungry, metabolism slows down to conserve energy and allow the human to continue living with less food.

Production of human red blood cells. A decrease in oxygen is detected by the kidneys and they secrete erythropoietin. This hormone stimulates the production of red blood cells.

Positive Feedback Loops and Homeostasis

• Used to eradicate a stimulus.

• Responses become more amplified over time.

• Not turned off until stimulus is completely removed.

• More intense than negative feedback loops.

• Could be life threatening (fever)

Positive Feedback Examples

Blood clotting. Injured tissue releases signal chemicals which activate platelets in the blood. An activated platelet releases chemicals which activate more platelets, causing the formation of a blood clot.

Lactation. As the baby nurses, there is a nerve response into the spinal cord and up into the hypothalamus of the brain, which then stimulates the pituitary gland to produce more prolactin to produce more milk.

Ovulation. A spike in estrogen during the follicular phase of the menstrual cycle causes ovulation

Enzymes and Homeostasis

• Enzymes are specialized proteins that catalyze reactions in our cells.

• Without proper enzyme function, cell death may occur.

• Enzymes play a homeostatic role in all of our human body systems.

Enzymes are proteins that speed up specific reactions in cells

Lower the energy required to activate a reaction (Activation Energy)

Specific to the reaction they accelerate

Unchanged from the reaction they accelerate

Work better at warmer temperatures, but not hot

Work better at particular pH levels

Work better at higher concentrations

Named after the substrate they catalyze

-ase suffix

The pH Scale the “power of Hydrogen”

Based on the negative exponent of [H+]pH=2 means [H+] = 1 x 10-2

or .01pH=13 means [H+] = 1 x 10-

13 or .0000000000001

Acid-Base Homeostasis

Buffers

Resist changes in pHAccept H+ when

solutions become too acidic (pH is too low)

Donate H+ when solutions become too basic (pH is too high)

Essential for maintaining homeostasis in living organisms

Buffer Capacitythe point at which the buffer can no longer absorb or contribute H+

Buffering AbilityWater vs. A Biological Substance

http://www.pearsonsuccessnet.com

4.4 pg 4

The Immune System

The homeostatic function of the Immune System is to defend against disease

Contact with infection

Immunization

Trans placental, breast milk

Antibiotics

At birth After birth

The Tissues and Organs of the Immune System

Skin- protective barrier. Tonsils and Adenoids-

trap germs that enter mouth and nose.

Bone Marrow- produces white blood cells.

Lymph nodes- produce and store cells that fight infection.

Spleen: filters blood. Thymus- small organ is

where T-cells mature . T-cells attack specific invaders.

Targeted Response over time