Section 1: Development and Physiology Part 2 Flashcards
Why don’t we generally study development in humans ?
- observation is difficult
- morally and ethically (no experiments on embryos
- We couldn’t nor would we want to breed humans
Why do we use model organisms ?
they were chosen for the ease with which they can be used to study in the laboratory, different models have different advantages
When is a something known as a model organism ?
When the primary research goal is to understand broad biological principles
Why were frogs chosen as a model organism ?
they were chosen as a good model for observing development of an animal embryo because their large eggs are easy to observe and manipulate + fertilization happens outside the mothers body
What are the most common invertebrates used for studying development ?
- Nematode worm (Caenorhabditis elegans) : small transparent body, from zygote to adult in 3 days, gnome has been sequenced, easy to detect mutant animals (disadvantage is its simplicity)
- fruit fly (Drosophila melanogaster): easily grown in lab, generation time is only two weeks + produces many offspring, embryos develop outside mothers body, genome has been sequenced
What are the most common vertebrates for studying development ?
-Frog (Xenopus laevis): ease of access and manipulation of egg + embryo, robust embryo, repid development, well-established system (disadvantage - no genetics, poorly characterized genome, cannot be bred for multiple generations)
-Chicken (Gallus Gallus): large easily obtainable eggs, development can be observed by cutting hole in egg, can be manipulated, complex development
-Mouse (Mus musculus): well studied, genome is almost completely sequenced, can manipulate mouse genes (disadvantages - development is hidden from us, embryo culture is limited, generation interval is long) VERY IMPORTANT MODEL
Why were sea urchins also used as a model organism ?
they were historically an important model, fertilization was studied, chance plays a role in the organisms chosen, found in the Naples bay, were easy to get and use, transparent eggs and embryos, echinoderms
What are the considerations when choosing a species for research ?
-Biological: is the organism suited for the type of study
- Practical: cost, space required, ease of handling and breeding
- Historical: if a model has been used in the past it is better understood
What does the study of development involve ?
- observing and describing embryos (descriptive embryology)
- manipulating embryos (experimental embryology)
- mapping the origin and destiny of cells (cell lineage analysis)
- altering genes and observing the affect on development (developmental genetics)
What is a plant often used for studying plant development ?
a small weed called Arabidopsis thaliana (member of the mustard family): short generations, small and easy to house, have genome sequenced, used for gene manipulation studies
What are the major differences between plant and animal development ?
- In animals but NOT in plants movements of cells and tissues are involved in transforming the embryo
- In plants, morphogenesis and growth are not limited to embryonic and juvenile periods
What is the cleavage stage in development ?
Cleavage: very rapid division of the fertilized egg (involves s phase, DNA synthesis), and m phase (mitosis), but skips G phase so there is no growth. The embryo does not enlarge
What is the gastrulation stage in development ?
It is marked by extensive cell movement, where the cells of the blastula become organized into three layers (3 layer embryo is a primitive gut) - 3 layered embryo is called a gastrula. They eventually develop into all the tissues and organs of a developed animal
What is a 3 layered embryo called, and what are the 3 layers ?
a gastrula, Ectoderm: outer, Mesoderm: middle, Endoderm: inside
What is an example of an organism that only has two layers in their embryo ?
a hydra only has two layers
Where was gastrulation classically studied ?
It was classically studied in frogs and other amphibians, bc the frog embryo is not so tiny, obvious poles in the embryo, ability to mark cells
What is lineage marking/cell fate mapping ?
you mark a cell by injecting a special dye early in development and observe where it and its decedent cells end up
What is convergent extension ?
embryo changes shape elongates its cells to meet and converge
What are the important features of gastrulation ?
-elaborate cell movement
-differentiation of cells into three broad types placed in the correct position
- allows communication between cells that are now set apart as different to one another
What does a complex organism require ?
it requires many hundreds of cell types to form structures and carry out specific functions
What do red blood cells do ?
They carry oxygen
How do cells differentiate ?
they become different because of differential gene expression, they express genes differently
What is a good example of cells differentiating ?
Muscle cells have to express myosin so that they have one of the structural proteins needed (myosin) to enable a muscle fiber to contract and red cells must express globin
What is transcription ?
When a gene is “turned on” its DNA sequence is used as a template for the synthesis of complementary RNA
What is mRNA ?
a single stranded polymer of ribonucleotides produced by transcription of a gene. directs the production of protein during translation, sequence of ribonucleotides is (complimentary to DNA)
What is translation ?
The production of protein from RNA, the sequence of amino acids that make up the protein depending on the genetic code carried by the RNA.
What do regulatory sequences do ?
they determine which cells express that gene and when they turn it on
What are promoters ?
they are regulatory sequences at the start of coding sequences and are needed for transcriptional machinery to assemble and begin to transcribe the DNA sequence into an RNA message or transcript
What is transcription initiation controlled by ?
they are controlled by proteins that interact with DNA
Where are enhancers located ?
they can be thousands of nucleotides away from the promoter or even downstream from the gene
What are factors that turn on a gene called ?
They are called activators
What do repressor proteins do ?
they bind to DNA regulatory sequences and destabilize transcription and turn the gene off (also known as silencers)
How fast does cell differentiation happen ?
it happens progressively as the embryo develops
What has happened as a differentiated cell shows up ?
the cell already produces the proteins that allow them to carry out their specialized role
What are Master regulatory genes ?
they are the genes that encode transcription and control cellular differentiation (they are the genes of most interest to developmental biologists)
What was an advance in developmental genetics that had a great impact ? 1/3
the isolation and study of the genes that regulate development
What was an advance in developmental genetics that had a great impact ? 2/3
The realization that such genes and basic development events are extremely highly conserved through evolution (observations made in one organism have wider relevance to all animals)
What was an advance in developmental genetics that had a great impact ? 3/3
development of molecular techniques to manipulate developmental genes and investigate their function
What was not initially appreciated in the study of development ?
the relevance of genetics to development was not appreciated at first (not until the 1940s)
How can we find the genes that guide development ?
by finding and studying individuals where development proceeds abnormally due to a single gene mutation (developmental mutants)
What are the two ways that developmental genes have been classified ?
- from spontaneous mutations (usually very few)
- large scale mutant screens: where animals are exposed to mutagens (chemical or radiation), this increases the frequency of genetic damage, then they are bred and they offspring are screened for mutants (this is kind of wild)
What are some factors that make it more feasible to screen for mutants ?
- space to house large number of animals
- person hours to screen large number of individuals
- phenotypes that are easy to observe
- short generation interval to accommodate breeding several generations
- simple genome (easy to map and sequence)
What is a particularly good species to do genetic screens ?
the fruit fly (Drosophila), one reason is because they have district appendages so mutations to appearance are easily identifiable
How are mutations classified ?
by describing the exact phenotype of a mutation and at what stage in development it is in
What are maternal affect genes ?
they are early acting genes that are active in the mother not the embryo, so the genetic product is supplied to by the egg (establish the axis’s)
What are segmentation genes ?
the first genes in the embryo’s DNA to be turned on/expressed, they are switched on by signals produced by the maternal affect genes (divide the embryo into segments along the axis)
What are homeotic genes ?
respond to signals produced y segmentation genes, are expressed in a segmented pattern determine segment identity
What happens if the bicoid function is mutated ?
it leads to no head and two tails (in fruit fly)
What does the bicoid gene control ?
it controls axis formation
Why is research on the bicoid gene important ?
- it identified a specific protein required for some of the earliest steps in pattern formation
-increased our understanding for the mothers role in the development of the embryo - showed a key developmental principle (a gradient of molecules can determine polarity and position of embryo
What is another gene affected by the maternal affect genes ?
segmentation genes, genes that affect the actual formation of segments
What are gap genes ?
act early and map out basic subdivisions along the anterior-posterior axis (mutations cause gaps in segmentation)
What are pair rule genes ?
they act later than gap genes and define the modular pattern in terms of pairs of segments (mutations result in embryos with half the normal segment number)
What are segment polarity genes ?
define segments and establish pattern with each segment (mutations produce embryos with normal segment number but part of each segment is altered/replaced by some other part)
Where are hox genes found ?
They are found in animals with an organized body plan, they are extremely valuable
What are three features of Hox genes ?
- they contain sub-class of highly conserved homeobox sequences, so they encode transcription factors
- They are involved in organizing the body plan of an animal
- They exist in clusters of similar genes in the genome
What are features of mammilian clusters ?
- DNA sequence is conserved
- Chromosomal arrangement of genes is conserved
- conserved the relative position along the AP axis of the embryo where they are expressed
What happens when hox genes are mutated in a mouse ?
They are not dramatic like those in a fruit fly, they are conserved at a functional level
How many hox genes are there in humans and mice ?
there are 39 hox genes that arrange in 4 clusters
In animals what is the space between cells called ?
interstitial fluid which links exchange surfaces to body cells
What is the hierarchy of organization ?
a) chemical level: molecule in the membrane that encloses a cell b) cellular level: cell in the stomach lining c) tissue level: layers of the tissue in the stomach d) organ level: the stomach e) body system level: digestive system
What are stem cells, what are the different kinds ?
undifferentiated cells that can give rise to specialized cells, there are embryonic stem cells, adult stem cells (tissue-specific), induced pluripotent stem cells (from skin cells)
What are the 4 primary types of tissues ?
- Epithelial tissue (exchange)
- Connective tissue (connection and support, includes blood and bone)
- Muscle tissue (electrically excitable)
- Nervous tissue (electrically excitable)
What do organs consist of ?
two or more types of primary tissues working together, example: stomach (wall lined with epithelial tissue, wall contains smooth muscle, nervous tissue controls contraction and gland secretion, connective tissue binds all other tissues together
What do body systems do ?
group of organs that perform a related function and help the body survive
What are the 11 systems of the mammalian body ?
circulatory, digestive, raspatory, urinary, skeletal, muscular, integumentary, immune, nervous, endocrine, reproductive
What is epithelial tissue ?
covers the outside of the body and lines the organs cavities within the body, contains cells that are closely joined. Shape of epithelial cells may be cuboidal, columnar, or squamous. They also give rise to glands
What is connective tissue ?
binds and supports other tissues, contains sparsely packed cells scattered throughout or extracellular matrix. matric consists of fibers in a liquid, jelly-like, or solid. It contains fibroblasts which secrete protein of extracellular fibers
What are the three types of connective tissue ?
- collagenous fibers (provide strength and flexibility)
- reticular fibers join connective tissue to adjacent tissues
- elastic fibers stretch and snap back to their original length
What is muscle tissue ?
responsible for nearly all movement, cells consist of filaments of the proteins actin and myosin, which together enables muscles to contract
What are the three types of muscle tissue in the vertebrate body ?
- Skeletal muscle - or striated muscle is responsible for voluntary movement
- smooth muscle - involuntary body activities
- cardiac muscle - contractions of the heart
What is nervous tissue ?
Functions in the receipt, processing and transmission of information. Contains Neurons, or nerve cells (transmit nerve impulses), Glial cells (support cells)
What is the nervous system?
a network of specialized cells-neurons that transmit signals along dedicated pathways,
-hard-wired, fast acting, electrical and chemical signaling, local cellular response, rapid response by target cells
What is the function of the endocrine system ?
chemical signaling by hormones is the function of the endocrine system, hormones transported in the blood, slower acting (minutes hours, days), chemical signaling, slower and often long-lasting responses of target cells
What are local regulators ?
molecules that act over short distances, reaching target cells solely by diffusion
What is paracrine signaling ?
target cells that lie near the secreting cells
What is autocrine signaling?
the target cell is also the secreting cell
What does endocrine signaling do ?
It maintains homeostasis, mediates responses to stimuli and regulates growth and development
What are the three major classes that hormones fall into ?
polypeptides, steroids and amines
What is endocrine tissue ?
grouped into ductless organs called endocrine glands, such as the thyroid and parathyroid glands, testes and ovaries
What are exocrine glands ?
salivary glands - have ducts to carry secreted substances onto body surfaces or cavities
What does the hypothalamus do ?
coordinates endocrine signaling - receives information from the nerves throughout the body and initiates appropriate neuroendocrine signals
What is the pituitary gland ?
composed of posterior pituitary (secretes ADH and oxytocin) and anterior pituitary (adenohypophysis, 7 hormones including growth)
What are synapses ?
neurons form specialized junctions with target cells
What do neurotransmitters do ?
diffuse short distances and bind to receptors on the target cell
What isa simple output ?
spinal chord reflex (reflexes in general)
What do sensory receptors do ?
transduce stimulus energy and transmit signals to the central nervous system for perception
What are the 4 basic functions of sensory pathways ?
-sensory reception
-transduction
-transmission
-perception
then it generates a response at the end
What happens when there is a stimulus ?
sensory reception: receptor detects stimulus
transduction: stimulus energy converted to electrical energy at cell membrane
transmission: action potentials fire in nerve afferents
perception: information relayed to and processed by CNS
response: effector organs
What are mechanoreceptors ?
they sense physical deformation caused by forms of mechanical energy: typically consists of ion channels linked to structures that end outside the cell (such as hairs (cilia)
What are chemoreceptors ?
they transmit information about the total solute concentration of a solution.
What are electromagnetic receptors ?
they detect electromagnetic energy such as light (photoreceptors), electricity and magnetism
What are thermoreceptors for ?
for heat and the cold
What do pain receptors do ?
they detect stimuli that reflect harmful conditions, respond to excess heat or chemicals released from damaged or inflamed tissues. Some receptors adapt over time
What makes areas on your skin more or less sensitive ?
the size of receptive fields makes your skin more sensitive, with small receptive fields more is felt and a region with large receptive field is less sensitive
How do photoreceptors work ?
light entering the eye strikes the retina, reaches the rods and cones (those are the two types of photoreceptors), then the neurons of the retina relay visual information to the optic nerve and brain
How does visual perception work ?
optic nerves meet at the optic chiasm near the center of the base of the cerebral cortex (x shape), sensations from the left visual field are transmitted to the right side of brain.
What is cognition ?
The process of acquiring knowledge, understanding through thought, experience and senses
How do bees use cognition to communicate ?
- bees initiate communicate angle and distance to food sources (angle from sun as direction, distance of waggles-bees butt lollll)
What is neuroscience ?
the study of behavior and biology
Do genes determine behavior ?
Nope !
What determines behavior ?
the brain, and your environment
What did Camillo Golgi do (1943-1926)
- Developed the Golgi staining method
- based on innate motivational drives
- promoted ‘reticular’ theory for continuity of brain organization
What did Santiago Ramon y Cajal do ?
- Used Golgi’s method for details anatomical analysis
- Discovered nerve cell growth cone
- Developed ‘neuron’ theory for brain anatomy
Where are most of a neurons organelles ?
they are in the cell body
What are dendrites ?
most neurons have them they are highly branched extensions that receive signals from other neurons
What is an axon ?
a much longer extension that transmits signals to other cells at synapses
How does information travel via synapse ?
information is transmitted from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle or gland cell)
What are neurons nourished and insulated by ?
they are glia or glia cells
What are the three stages that the nervous systems process information ?
sensory input, integration and motor output
What is the central nervous system ?
this is where integration takes place; includes the brain and nerve cord
What is the peripheral nervous system ?
carries info into and out of the central nervous system (CNS)
What is membrane potential ?
the voltage that each cell has that goes through the plasma membrane
What is resting potential ?
the membrane potential of a neuron not sending signals
What are changes in membrane potentials called ?
action potentials
Why do changes in membrane potential occur ?
they change because neurons contain gated ion channels that open and close due to stimuli, and voltage-gated ion channels open or close in response to a change in voltage across the plasma membrane
What is hyperpolarization ?
When gated K+ channels open and potassium diffuses out making the inside of the cells more negative (increase in magnitude of membrane potential)
What is depolarization ?
opening other types of ion channels triggers a depolarization, a reduction of the magnitude of membrane polarization
What are graded potentials ?
changes in polarization where the magnitude of the change varies with the strength of the stimulus
In what direction is does action potential go ?
it only travels in one direction toward the synaptic terminals, inactive Na+ channels behind the zone of depolarization prevent the action potential from travelling backwards
In vertebrates what are axons insulated by ?
they are insulated by a myelin sheath which causes action potentials speed to increase
What is a myelin sheath made of ?
they are made by glia - oligodendrocytes in the central nervous system and by Schwann cells in the Posterior nervous system (PNS)
Where are the voltage-gated sodium channels ?
they are restricted to the nodes of Ranvier, gaps in the myelin sheath
what is saltatory conduction ?
action potentials in myelinated axons jumping between the nodes of Ranvier
Where and how to neurons communicate ?
They communicate through synapses, electrical current flows from one neuron to another through gap junctions (electrical synapses). Chemical synapses - chemical neurotransmitter carries information between neurons
What are the two categories of postsynaptic potentials ?
- Excitatory postsynaptic potentials: depolarizations that bring the membrane potential toward threshold
- Inhibitory postsynaptic potentials: hyperpolarization’s that move the membrane potential farther from the threshold
What happens after a response is triggered ?
chemical synapses return to its resting state, the neurotransmitter molecules are cleared from the synaptic cleft
What does cocaine do to neurotransmitters ?
cocaine prevent re-uptake of dopamine, leading to hyperdopaminergic activity
