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AP Biology Big Idea #3
Transcript of AP Biology Big Idea #3
involves cellular and molecular mechanisms. Gene regulation results in differential gene expression, leading to cell specialization.
A variety of intercellular and intracellular signal transmissions mediate gene expression. Heritable information provides for continuity of life. DNA, and in some cases RNA, is the primary source of heritable information.
In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization.
The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring.
The inheritance pattern of many traits cannot be explained by simple Mendelian genetics Living systems
store, retrieve, transmit, and
respond to information essential to life processes. 3A: Heritable information provides for continuity of life.
3B: Expression of genetic information involves cellular and molecular mechanisms.
3C: The processing of genetic information is imperfect and is a source of genetic variation
3D: Cells communicate by generating, transmitting and receiving chemical signals.
3E: Transmission of information results in changes within and between biological systems. The processing of genetic information
is imperfect and is a source of genetic variation Changes in genotype can result in changes in phenotype.
Biological systems have multiple processes that increase genetic variation.
Viral replication results in genetic variation, and viral infection can introduce genetic variation into the hosts. Cells communicate by generating,
transmitting and receiving chemical signals. Cell communication processes share common features that reflect a shared evolutionary history.
Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling.
Signal transduction pathways link signal reception with cellular response.
Changes in signal transduction pathways can alter cellular response. Transmission of information results in
changes within and between biological systems. Individuals can act on information and communicate it to others.
Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses. Living systems store, retrieve, transmit, and respond to information essential to life processes. BIG IDEA #3 Genetic information is transmitted from
one generation to the next through DNA or RNA. DNA=storage for genetic information
Prokaryotes= circular chromosomes, Eukaryotes= multiple linear
plasmids=double stranded DNA molecule, circular extra-chromosomal
Proof that DNA is genetic info?
Hershey Chase-Blender, labeled DNA and Proteins
Avery-MacLeod-McCarty, bacterial transformation caused by DNA
Watson, Crick, Franklin, Wilkins- double helix structure, x-ray image
DNA replication ensures continuity of hereditary information
replication is semi conservative with leading and lagging strand
Retroviruses is a special case: from RNA to DNA, by reverse transcriptase, an enzyme that copies the viral RNA genome into DNA. This DNA integrates into the host genome DNA and RNA molecules have structural
similarities and differences that define function Nucelotide= sugar phosphate backbone+nitrogenous base attached 3' to 5', but structural differences do exist (u, single strand, ribose)
A--T or A--U, and C--G (purines/G/A with pyrimidines T/U/C
sequence and structure of RNA determines function:
mRNA, tRNA, rRNA, RNAi (regulation of gene expression)
Central Dogma: DNA-->RNA-->Protein
RNA-polymerase reads the DNA molecule in the 3' to 5' direction
Eukaryotic mRNAs are modified with cap, poly-A tail, and splicing
Translation occurs in the cytoplasm on ribosomes
Prokaryotic organisms couple transcription to translation
ribosome's rRNA interacts with mRNA to begin tln at start codon (mRNA read in triplet codons)
tRNA brings correct amino acid, peptide bond formed
stop codon releases polypeptide chain! More Molecular Genetics Phenotypes are determined through protein activities. (enzymatic activities ex.)
Genetic engineering techniques can manipulate the heritable information of DNA and, in special cases, RNA. (pick one below to review!)
Restriction enzyme analysis of DNA
Polymerase Chain Reaction (PCR)
Learn one example below of genetic engineering
Genetically modified foods
Pharmaceuticals, such as human insulin or factor X The cell cycle is a complex set of stages that is highly regulated with checkpoints, which determine the ultimate fate of the cell. Interphase- growth, synthesis, growth (prep for mitosis)
Checkpoints regulate the cell cycle like Mitosis-promoting factor (MPF)
Cyclins and cyclin-dependent kinases control the cell cycle.
Cyclins are a family of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (CDK) enzymes.
Mitosis alternates with interphase in the cell cycle or cell enters G0 phase Mitosis passes a complete genome from the
parent cell to daughter cells. Mitosis occurs after DNA replication and results in 2 identical 2n daughter cells
plays a role in growth, repair, and asexual reproduction
a continuous process with observable structural features along the mitotic process,
LEARN the order of the processes (replication, alignment, separation).
Memorization of the names of the phases of mitosis is beyond the scope of the AP Exam.
Meiosis, a reduction division, followed by fertilization ensures genetic diversity in sexually reproducing organisms.
production of gametes results in 4 haploid (n) daughter cells with mixed DNA from each parent
homologous chromosomes are paired, with one from the maternal parent and one from the paternal parent- alignment is random
homologous chromatids undergo “crossing over,” which increasing genetic variationFertilization involves the fusion of two gametes, increases genetic variation in populations by providing for new combinations of genetic information in the zygote, and restores the diploid number of chromosomes. Mendelian Genetics probability applied when analyzing path of single gene to offspring
Segregation and Independent Assortment of genes
only work if genes are on different chromosomes,
otherwise LINKED= probability that they will segregate as a unit is a function of the distance between them
data about P, F1 and F2 generations gives mode of inheritance
Errors in this process (nondisjunction, ex.) lead to disorders like Down's Syndrome a.k.a. trisomy 21
Ethical issues abound!
can someone own your genetic information?
should a prenancy with confirmed trisomy 21 be terminated? Non-Mendelian Inheritance Many traits controlled by multiple genes
Some traits are X linked (or Y linked)
Chloroplasts and mitochondria are randomly assorted to gametes and daughter cells
In animals, mitochondria inherited from egg (therefore, Mother only)
no epistasis or pleiotropy on exam :( Regulation of Gene Expression DNA regulatory sequences, regulatory genes, and small regulatory RNA
Regulatory sequence on DNA interacts with protein to control transcription, ex. Promotors, Terminators, Enhancers
Regulatory genes code for regulatory proteins
positive and negative controls regulate gene expression in bacteria and viruses
inducer stimulates transcription of genes, repressors inhibit by interacting with regulatory sequence or protein
Regulatory proteins inhibit by binding to DNA and blocking transcription (negative control) or stimulate gene expression by binding to DNA and stimulating transcription (positive control) [or block repressor]
certain genes are always "on" like rRNA genes
Regulation in Eukaryotes is complex: transcription factors, regulatory genes, etc
the amounts and types of transcription factors binding to DNA determine expression levels
phenotypic differences in orgs with similar genomes Signal Transmission and Gene Expression Regulation of Gene expression.
Expression of the SRY gene triggers the male sexual development pathway in animals
Regulation of Cell function.
Morphogens stimulate cell differentiation and development. Changes in Genotype impact Phenotype a DNA mutation can alter protein structure/abundance, so mutations could be positive, negative, or neutral but are primary source of variation
mutation caused by errors in DNA replication, repair, or other mutagens
Errors in mitosis/meiosis also can result in developmental disabilities
natural selection determines whether mutation remains in population
Sickle Cell Anemia- heterozygote advantage though homozygous recessive is not good
eventually evolutionary change can result! Increasing Genetic Variation mutations increase variation
genetic transfer in prokaryotes via
transformation (uptake of naked DNA),
transduction (viral transmission of genetic information),
conjugation (cell-to-cell transfer) and
transposition (movement of DNA segments within one molecule)
Sexual reproduction in eukaryotes
crossing-over during meiosis
random assortment of chromosomes during meiosis
evolutionarily conserved process! Virus Genetics Genetic Variation created through these mechanisms:
highly replicative capabilities
many progeny created simultaneously in lytic cycle
host cell's replicative mechanism is hijacked and introduces mutations--RNA viruses have higher rates of mutation because they lack error-checking mechanisms
Thus, HIV is particularly infectious
Virus can integrate into host genome during lysogenic cycle Signal Transduction and evolution Communication involves transduction of stimulatory or inhibitory signals from other cells, organisms or the environment
Prokaryotes: signals allow for response to environment, like movement
Multicellular orgs: coordinate the activities within individual cells
ex. epinephrine stimulates glycogen breakdown Cell Communication Cells communicate by cell-to-cell contact
ex. antigen-presenting cells (APCs), helper T-cells and killer T-cells.
over short distances by using local regulators that target cells nearby
ex. Neurotransmitters between neurons in the synaptic cleft
Signals released by one cell type can travel long distances to target cells of another cell type
Endocrine signals are produced by endocrine cells that release signaling molecules, which are specific and can travel long distances through the blood to reach all parts of the body (HORMONES)
ex. Insulin stimulates uptake of glucose by cells and thus regulates blood sugar levels Signals outside cause responses inside cells Unique membrane proteins recognize chemical signals one-to-one
binding of chemical signal induces shape change in protein
ex. neurotransmitters bind and protein changes conformation allowing ion flow into post synaptic neuron
Signal transduction is the 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 often essential to the function of the cascade.
ex. flow of calcium ions through voltage gated channels in pre-synaptic neuron
Many signal transduction pathways include:
phosphorylation cascades where phosphate groups are added to successive proteins Changes in pathways alter Responses Conditions where signal transduction is blocked or defective can be deleterious, preventative or prophylactic.
ex. birth control pills
ex. psychoactive drugs Communication between Organims Organisms exchange information with each other in response to internal changes and external cues, which can change behavior.
Living systems have a variety of signal behaviors or cues that produce changes in the behavior of other organisms and can result in differential reproductive success.
ex. territorial marking with cats
Animals use visual, audible, tactile, electrical and chemical signals to indicate dominance, find food, establish territory and ensure reproductive success.
ex. Zebra finch songs
Responses to information and communication of information are vital to natural selection and evolution
Natural selection favors innate and learned behaviors that increase survival and reproductive fitness.
Cooperative behavior tends to increase the fitness of the individual and the survival of the population.
ex. pack behavior of many animal species Review the Nervous System! The neuron is the basic structure of the nervous system that reflects function.
Action potentials propagate impulses along neurons.
Membranes of neurons are polarized by the establishment of electrical potentials across the membranes.
In response to a stimulus, Na+ and K+ gated channels sequentially open and cause the membrane to become locally depolarized.
Na+/K+ pumps, powered by ATP, work to maintain membrane potential.Transmission of information between neurons occurs across synapses.
neurotransmitters cause excitatory or inhibitory repsonse
Different regions of the vertebrate brain have different functions.