study study study

hi! i'm amber, and this is my sideblog for notes. taking notes online really helps me, so here we are! currently studying : sat bio

[ambersdesk]

sat biology: point mutations

point mutations - base-pair substitution, change in a single nucleotide

missense mutation

the sequence GAG in dna codes for the amino acid leucine. however, if a base mutates to become GCG, the sequence will code for arginine

nonsense mutation

the sequence ATG in dna goes for tyrosine, but when the last base is changed so the sequence is ATT, a stop codon occurs and cuts the amino sequence short

silent mutation

sometimes, a mutation will not show up in an individual’s phenotype because there are many sequences that code for one amino acid. for example, both AGT and AGA code for serine

[ambersdesk]

sat biology: gene regulation and the Lac operon

all cells in your body have the same dna. however, a skin cell does not use the same regions of dna as a muscle cell

operon - cluster of functional genes plus the switches that turn them on and off

promoter - binding side of rna polymerase

tata box - alternating sequence of thymine and adenine that helps rna polymerase bind 

Lac operon - normally turned off unless actively induced or triggered

ex. a bacterium will metabolize glucose when there is more glucose than lactose in it’s environment, but when there is more lactose available than glucose, lactose will bind to the repressor of the operator. this changes the shape of the repressor and allows for the genes for beta galactase to be copied so they can be translated into the beta galactase enzyme

[ambersdesk]

sat biology: nitrogen cycle

1. nitrogen exists in the atmosphere as nitrogen gas

2. nitrogen fixing bacteria convert nitrogen gas into ammonia and ammonium

3. nitrifying bacteria convert ammonia and ammonium into nitrates and nitrites

4. plants use nitrates and nitrites

5. consumers eat plants, nitrogen travels up the food chain

6. consumers and plants die. their nitrogen is then recycled back into the soil by decomposers. decomposers can also fix nitrogen into ammonia

7. nitrifying bacteria convert ammonia into nitrates and nitrites for plants to use

7. denitrifying bacteria use nitrate reductase recycle nitrates and nitrites back into the atmosphere as nitrogen gas

8. nitrogen fixing bacteria fix nitrogen gas into ammonia and ammonium

and the cycle continues...

[ambersdesk]

sat biology: nitrogen cycle

nitrogen exists in the air as nitrogen gas

nitrogen fixation - nitrogen fixing bacteria live in water and soil, some form symbiotic relationship with root nodules of plants. these bacteria convert atmospheric nitrogen (n2) to ammonia (nh3), which when combined with water to form ammonium (nh4+) can be used by plants

nitrogenase is the only biological enzyme that can break the triple bond in nitrogen gas

lightning can also break bonds between nitrogen gas

ammonia can also be made by decomposers

nitrifying bacteria convert ammonium (nh4+) into nitrates (no3-) and nitrites (n02-)

denitrifying bacteria - use nitrate reductase to release nitrogen gas back into the atmosphere

[ambersdesk]

sat biology: endocrine hormones

anterior pituitary

growth hormone - stimulates growth of bones

luteinizing hormone - stimulates ovaries and testes

thyroid-stimulating hormone - stimulates thyroid gland

adrenocorticotropic hormone - stimulates adrenal cortex to secrete glucocorticoids

follicle stimulating hormone - stimulates gonads to produce sperm and ova

posterior pituitary

oxytocin - stimulates contractions of uterus and mammary glands

antidiuretic hormone - promotes water retention by kidneys

thyroid

thyroxin - controls metabolic rate

calcitonin - lows blood calcium levels

parathyroid

parathormone - raises blood calcium levels

adrenal cortex

glucocorticoids - raise blood sugar levels

adrenal medulla

epinephrine and norepinephrine - raise blood sugar levels by increasing rate of glycogen breakdown by liver

pancreas

insulin - lowers blood glucose levels

glucagon - raises blood glucose levels

thymus

thymosin - stimulates t lymphocytes

pineal

melatonin - involved in biorhythms

ovaries

estrogen - stimulates uterine lining, promotes development and maintenance of primary and secondary characteristics of female

progesterone - promotes uterine lining growth

testes

androgens - support sperm production and promote secondary sex characteriestics

[ambersdesk]

sat biology: endocrine glands

hypothalamus - bridge between nervous and endocrine systems, produces oxytocin and antidiuretic hormone (adh)

anterior pituitary - growth hormone (gh), luteinizing hormone (lh), thyroid-stimulating hormone (tsh), adrenocorticotropic hormone (adth), follicle-stimulating hormone (fsh)

posterior pituitary - oxytocin,, antidiuretic hormone (adh)

thyroid - thyroxin, calcitonin

parathyroid - parathromone

adrenal cortex - glucocorticoids

adrenal medulla - epinephrine, norepinephrine

pancreas, islets of Langehans - insulin, glucagon

thymus - located in neck, t cells mature here, thymosin

pineal - located in brain, melatonin

ovaries - estrogen, progesterone

testes - androgens

[ambersdesk]

sat biology: animal physiology

all animals are heterotrophs and ingest nutrients

movement and locomotion - all animals have movement

movement can refer to beating of cilia or waving tentacles

it can also refer to locomotion, movement from place to place. some animals, such as hydra and sponges, are sessile: they do not move from place to place. 

structure:

some mollusks have a mantle that secretes a shell. some arthropods have a chitin exoskeleton that must be shed when the animal grows. nematodes, planaria, and annelids have a hydrostatic skeleton, a body compartment filled with fluid. chordates have an endoskeleton of bone and cartilage that grows and the animal grows. 

bones connect to bones via ligaments. tendons connect bones to muscles.

body temperature - most life exists within 0ºc and 50ºc

animals must seek out or create a suitable environment. some animals change behaviors, while others evolve.

ectotherm: heated from outside, “cold-blooded”

endotherm/homeotherm: maintains a constant body temperature, “warm-blooded”

being an endotherm may have given birds and mammals an evolutionary edge: they could be active at any time

excretion - removal of metabolic wastes including water, carbon dioxide, and nitrogenous wastes

ammonia is very water-soluble, highly toxic, and excreted by organisms that live in water

urea is not as toxic as ammonia and excreted by earthworms and humans

uric acid is pastelike, not water soluble, and not very toxic. uric acid minimizes water loss

[ambersdesk]

sat biology: proof of evolution

vocab: 

evolution - change in genes of a population over time

microevolution - change in one gene pool of a population

macroevolution - speciation, the formation of a new species

population - all the members of one species in one place

evidence of evolution: 

fossil record - shows the existence of species that have become extinct or have evolved into other species

the earth is about 4.6 billion years old. prokaryotic cells are the oldest fossils. many transitional fossils have been foudn that link extinct fossils to modern species. ex. archaeopteryx and hyracotherium (eohippus)

comparative anatomy - similar anatomical structures show a common ancestor

homologous structures may vary in function, but show common ancestry and diverenge from that common ancestor. ex. bat wing, whale lateral wing, human arm

analogous structures have the same function and show adaptation to a similar environment. these are evidence of convergent evolution. ex. bat and fly wings

vestigal structures are evidence that anatomy has evolved. these structures are useless to the modern animal. ex. hip bones in whales

comparative biochemistry - organisms with a common ancestor will have common biochemical pathways. ex. humans and mice, mice are used for medical research

comparative embryology - closely relation organisms go through similar stages in embryonic development. ex. vertebrate embryos have gill pouches at one stage

molecular biology - all aerobic animals have cytochrome c for respiration, cytochrome c amino sequence is more similar if the animals are closely related. ex. cytochrome c for humans and chimpanzees is identical

biogeography - continental drift states that 250 million years ago, the continents were in a single supercontinent named Pangaea. ex. marsupials migrated by land from south america across antartica to australia before the continents separated