Big Idea 3 Review: Living systems store, retrieve, transmit, and respond to information essential to life processes.

spiritualblurtedAI and Robotics

Nov 24, 2013 (3 years and 8 months ago)

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Big Idea 3 Review: Living systems store, retrieve, transmit, and respond to

information essential to life processes.

Explaining how the structural features of DNA and RNA allow heritable information to be replicated,
stored expressed, and transmitted to
future generations.


Explaining how the steps in the cell cycle allow transmission of heritable information between
generations and contribute to genetic diversity.


Meiosis reduces the number of chromosome sets from diploid to haploid

Like mitosis, meiosi
s is preceded by the replication of chromosomes

Meiosis takes place in two sets of cell divisions, called meiosis I and meiosis II

The two cell divisions result in four daughter cells, rather than the two daughter cells in mitosis

Each daughter cell has o
nly half as many chromosomes as the parent cell


In the first cell division (meiosis I), homologous chromosomes separate

Meiosis I results in
two

haploid daughter cells with
replicated

chromosomes

In the second cell division (meiosis II), sister chromatids

separate

Meiosis II results in
four

haploid daughter cells with
unreplicated

chromosomes


Three events are unique to meiosis, and all three occur in meiosis l:

Synapsis and crossing over in prophase I: Homologous chromosomes physically connect and exchang
e
genetic information

At the metaphase plate, there are paired homologous chromosomes (tetrads), instead of individual
replicated chromosomes

At anaphase I, it is homologous chromosomes, instead of sister chromatids, that separate and are
carried to opposi
te poles of the cell


Evolutionary Significance of Genetic Variation Within Populations

Natural selection results in accumulation of genetic variations favored by the environment

Sexual reproduction contributes to the genetic variation in a population, wh
ich ultimately results from
mutations


Genetic variation produced in sexual life cycles contributes to evolution

Mutations (changes in an organism’s DNA) are the original source of genetic diversity

Mutations create different versions of genes

Reshuffling
of different versions of genes during sexual reproduction produces genetic variation


Origins of Genetic Variation Among Offspring

The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation
that arises in each
generation

Three mechanisms contribute to genetic variation:

Independent assortment of chromosomes

Crossing over

Random fertilization

Independent Assortment of Chromosomes


Homologous pairs of chromosomes orient randomly at metaphase I of meiosis

In indepe
ndent assortment, each pair of chromosomes sorts maternal and paternal homologues into
daughter cells independently of the other pairs

The number of combinations possible when chromosomes assort independently into gametes is 2
n
,
where
n

is the haploid number

For humans (
n

= 23), there are more than 8 million (2
23
) possible combinations of chromosomes


Random Fertilization

Random fertilization adds to genetic variation because any sperm can fuse with any ovum (unfertilized
egg)

The fusion

of gametes produces a zygote with any of about 64 trillion diploid combinations

Crossing over adds even more variation

Each zygote has a unique genetic identity


Evolutionary Significance of Genetic Variation Within Populations

Natural selection results i
n accumulation of genetic variations favored by the environment

Sexual reproduction contributes to the genetic variation in a population, which ultimately results from
mutations


Using at least two commonly used technologies, describe how humans manipulate

heritable information
and possible consequences.


Determining Gene Function

One way to determine function is to disable the gene and observe the consequences

Using
in vitro

mutagenesis, mutations are introduced into a cloned gene, altering or destroying i
ts
function

When the mutated gene is returned to the cell, the normal gene’s function might be determined by
examining the mutant’s phenotype

In nonmammalian organisms, a simpler and faster method, RNA interference (RNAi), has been used to
silence
expression of selected genes


Identifying mathematical evidence that supports the roles of chromosomes and fertilization in the
passage of traits from parent to offspring. Justify the effects of a change in the cell cycle mitosis and/or
meiosis will have o
n chromosome structure, gamete viability, genetic diversity, and evolution


Predict possible effects that alterations in the normal process of meiosis will have on the phenotypes of
offspring compared to the normal situation and connect the outcomes to iss
ues surrounding human
genetic diseases.

Down’s syndrome (trisomy 21), Kleinfelter’s syndrome (XXY), Turner’s syndrome (XO)


Non
-
disjunction

Failure of chromosome pairs to separate during meiosis

Results in gametes with too many or too few chromosomes


-
An
euploidy: abnormal # of a certain chromosome


-
Polyploidy: more than 2 complete chromosome sets

An embryo needs at least one X chromosome to survive

Justifying whether a given data set supports Mendelian inheritance. Apply mathematical routines to
determin
e Mendelian patterns of inheritance provided by data sets, and, using appropriate examples,
explain at the chromosome, cellular, and offspring (organism) levels why certain traits do or do not
follow Mendel’s model of inheritance


Extending Mendelian Genet
ics for a Single Gene

Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following
situations:

When alleles are not completely dominant or recessive

When a gene has more than two alleles

When a gene produces multip
le phenotypes


Pleiotropy

Most genes have multiple phenotypic effects, a property called pleiotropy

For example, pleiotropic alleles are responsible for the multiple symptoms of certain hereditary
diseases, such as cystic fibrosis and sickle
-
cell disease


Using appropriate examples, explaining how gene regulation allows for cell specialization and efficient
cell function. Justify how various modes of gene regulation (positive and negative) can explain the
differences seen at the cellular, organismal, and p
opulation level. Predict how changes in regulation will
affect cellular functions

Different cell types result from differential gene expression in cells with the same DNA

Differences between cells in a multicellular organism come almost entirely from gene
expression, not
differences in the cells’ genomes

These differences arise during development, as regulatory mechanisms turn genes off and on


Differential Gene Expression

Differences between cell types result from differential gene expression, the
expression of different
genes by cells within the same genome

In each type of differentiated cell, a unique subset of genes is expressed


Many key stages of gene expression can be regulated in eukaryotic cells

Regulation of Transcription Initiation

Chromat
in
-
modifying enzymes provide initial control of gene expression by making a region of DNA
either more or less able to bind the transcription machinery


Organization of a Typical Eukaryotic Gene

Associated with most eukaryotic genes are control elements, se
gments of noncoding DNA that help
regulate transcription by binding certain proteins

Control elements and the proteins they bind are critical to the precise regulation of gene expression in
different cell types


The Roles of Transcription Factors

To initia
te transcription, eukaryotic RNA polymerase requires the assistance of proteins called
transcription factors

General

transcription factors are essential for the transcription of
all

protein
-
coding genes

In eukaryotes, high levels of transcription of partic
ular genes depend on control elements interacting
with
specific

transcription factors

Some transcription factors function as repressors, inhibiting expression of a particular gene

Some activators and repressors act indirectly by influencing chromatin struc
ture

Operons: The Basic Concept

In bacteria, genes are often clustered into operons, composed of

An operator, an “on
-
off” switch

A promoter

Genes for metabolic enzymes

An operon can be switched off by a protein called a repressor

A corepressor is a small m
olecule that cooperates with a repressor to switch an operon off


Repressible and Inducible Operons: Two Types of Negative Gene Regulation

A repressible operon is one that is usually on; binding of a repressor to the operator shuts off
transcription

The
trp

operon is a repressible operon

An inducible operon is one that is usually off; a molecule called an inducer inactivates the repressor and
turns on transcription

The classic example of an inducible operon is the
lac

operon, which contains genes coding
for enzymes
in hydrolysis and metabolism of lactose


Using an appropriate example, describing a signal transduction pathway mechanism that affects protein
expression.


Local and Long
-
Distance Signaling

Cells in a multicellular organisms

communicate by chemical messengers

Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells

In local signaling, animal cells may communicate by direct contact


Local and Long
-
Distance Signaling

Cells in a multicellu
lar organisms communicate by chemical messengers

Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells

In local signaling, animal cells may communicate by direct contact


Describing the basic processes by which a
change in a DNA sequence results in a change in a peptide
sequence.

Point mutations can affect protein structure

and

function

Mutations are changes in the genetic material of a cell or virus

Point mutations are chemical changes in just one base pair of a g
ene

The change of a single nucleotide in a DNA template strand leads to production of an abnormal protein


Types of Frame
-
shift Mutations

mutations within a gene can be divided into two general categories

Base
-
pair insertions

Base
-
pair deletions


Describi
ng two processes that increase genetic variation and explaining how genetic variation allows for
natural selection within a population

Mutations, crossing over, independent assortment, sexual reproduction


Describing several mechanisms that result in
increased genetic variation and rapid evolution of viruses.

RNA viruses have no “proof
-
reading” of their nucleotides so mutations go unchanged; proviruses can
pick up DNA from their host and incorporate it into their genome


Describing how both plants and
animals use cell
-
to
-
cell communication for cellular processes using an
appropriate example from each.

Insulin/glucagon in animals

De
-
etiolation, phototropism, photoperiodism in plants


Signal transduction pathways link signal reception to response

Plants h
ave cellular receptors that detect changes in their environment

For a stimulus to elicit a response, certain cells must have an appropriate receptor

A potato left growing in darkness produces shoots that look unhealthy and lacks elongated roots

These are m
orphological adaptations for growing in darkness, collectively called etiolation

After exposure to light, a potato undergoes changes called de
-
etiolation, in which shoots and roots grow
normally


A potato’s response to light is an example of cell
-
signal pr
ocessing

The stages are reception, transduction, and response


Phytochromes exist in two photoreversible states, with conversion of P
r

to P
fr

triggering many
developmental responses


Explaining key features of models that illustrate how changes in a signal

pathway can alter cellular
responses Construct a model that illustrates how chemical signals can alter cellular responses. Predict
the effects of changes in the signal pathway on cellular responses using appropriate examples.


Type I diabetes mellitus (in
sulin
-
dependent) is an autoimmune disorder in which the immune system
destroys pancreatic beta cells

Type II diabetes mellitus (non
-
insulin
-
dependent) involves insulin deficiency or reduced response of
target cells due to change in insulin receptors


Invertebrate regulatory systems also involve endocrine and nervous system interactions

Diverse hormones regulate homeostasis in invertebrates

In insects, molting and development are controlled by three main hormones:

Brain hormone stimulates release of
ecdysone from the prothoracic glands

Ecdysone promotes molting and development of adult characteristics

Juvenile hormone promotes retention of larval characteristics


Describing how behavior is modified in response to external and internal cues for both an
imals and
plants using appropriate examples from each.


In male stickleback fish, the stimulus for attack behavior is the red underside of an intruder

When presented with unrealistic models, as long as some red is present, the attack behavior occurs


Dieta
ry Influence on Mate Choice Behavior

An example of environmental influence is the role of diet in mate selection by
Drosophila mojavensis

Experiments have demonstrated that food eaten by larvae influences later mate choice in females

It has been proposed t
hat the physiological basis for the observed mate preferences was differences in
hydrocarbons in the exoskeletons of the flies


Chemical Communication

Many animals that communicate through odors emit chemical substances called pheromones

When a minnow or c
atfish is injured, an alarm substance in the fish’s skin disperses in the water,
inducing a fright response among fish in the area


Gravity

Response to gravity is known as gravitropism

Roots show positive gravitropism

Stems show negative gravitropism


Mech
anical Stimuli

The term
thigmomorphogenesis

refers to changes in form that result from mechanical perturbation

Rubbing stems of young plants a couple of times daily results in plants that are shorter than controls

Thigmotropism is growth in response to tou
ch

It occurs in vines and other climbing plants

Rapid leaf movements in response to mechanical stimulation are examples of transmission of electrical
impulses called action potentials


During drought, plants respond to water deficit by reducing
transpiration

Deeper roots continue to grow

Heat
-
shock proteins help plants survive heat stress

Altering lipid composition of membranes is a response to cold stress


Plants defend themselves against herbivores and pathogens

Plants counter external threats
with defense systems that deter herbivory and prevent infection or
combat pathogens


Describing how the nervous system detects external and internal stimuli and transmits signals along and
between nerve cells Describe how changes within nerve cells and the

nervous system produce
responses to the stimuli


The Resting Potential

Resting potential is the membrane potential of a neuron that is not transmitting signals

Resting potential depends on ionic gradients across the plasma membrane

Concentration of Na
+

is higher in the extracellular fluid than in the cytosol

The opposite is true for K
+


Production of Action Potentials

Depolarizations are usually graded only up to a certain membrane voltage, called the threshold

A stimulus strong enough to produce depola
rization that reaches the threshold triggers a response
called an action potential

An action potential is a brief all
-
or
-
none depolarization of a neuron’s plasma membrane

It carries information along axons

Voltage
-
gated Na
+

and K
+

channels are involved in
producing an action potential

When a stimulus depolarizes the membrane, Na
+

channels open, allowing Na
+

to diffuse into the cell

As the action potential subsides, K
+

channels open, and K
+

flows out of the cell

During the refractory period after an action p
otential, a second action potential cannot be initiated


Conduction of Action Potentials

An action potential can travel long distances by regenerating itself along the axon

At the site where the action potential is generated, usually the axon hillock, an
electrical current
depolarizes the neighboring region of the axon membrane


Neurons communicate with other cells at synapses

In an electrical synapse, current flows directly from one cell to another via a gap junction

The vast majority of synapses are chem
ical synapses

In a chemical synapse, a presyn
aptic neuron
releases chemical neurotransmitters stored in the synaptic
terminal

When an action potential reaches a terminal, the final result is release of neurotransmitters into the
synaptic cleft


Direct Syna
ptic Transmission

Direct synaptic transmission involves binding of neurotransmitters to ligand
-
gated ion channels

Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential

After release, the neurotransmitter diffuses out of
the synaptic cleft

It may be taken up by surrounding cells and degraded by enzymes