Week 5 - Genetics Flashcards
What is DNA?
Deoxyribonucleic acid
Why do genes come in pairs?
They are generally aligned along chromosomes (strands of genes).
What does RNA do?
Ribonucleic acid is synthesised from the blueprint of DNA.
What does messenger RNA do?
servse as a template for the syntehsis of protein molecules.
What are the four “bases” of DNA?
Adenine, Guanine, Cytosine and Thymine.
How do bases pair up?
Guanine - Cytosine
Adenine - Thymine
What determines one amino acid?
A sequence of RNA (3 bases) determine one amino acid.
When does the central nervous system begin to develop?
Around 2 weeks after conception.
What does the embryo look like at 2 weeks?
Like an elongated plate
Does the embryo have neural tissue at 2 weeks?
No.
When does the neural plate invaginate?
at around 20 days.
When do ganglia form?
24 days.
By what time do the hindbrain, midbrain and forebrain diffeerentiate?
by 7 weeks.
By what time is the basic layout of the brain developed?
11 weeks.
At birth, how much does the brain weigh?
About 350 grams.
At the end of the first year, how much does the brain weigh?
Around 1kg (close to adult weight of 1200-1400 grams).
What are the 5 distinct stage in the development of neurons?
Proliferation, Migration, Differentiation, Myelination, Synaptogenesis.
What happens during Proliferation?
Cells in ventricles divide - some become primite neurons and glia that go to new destination.
What happens during Migration?
cells follow chemical path toward final destination.
What happens during Differentiation?
axons and dendrites are formed while migrating
What happens during Myelination?
addition of insulating sheath that speeds transmission.. Doesn’t apply to all neurons. Improves speed and efficiency of transmission. This can take up to 20 years of age.
What happens during Synaptogenesis?
Formation of synapses, continues throughout life.
What determines the survival of a neuron?
Two conditions:
- must form synapse with target cell and receive a nerve growth factor (a neurotrophin) from that cell
- must also be stimulated to release neurotransmitters into synapse
What is Apoptosis?
programmed cell death that occurs when synapses receive little nerve growth factor (NGF). This happens if a neuron doesn’t meet both requirements.
What happens during migration?
The neuron plate sinks down to form invagination. Epidermus cells are at the ends of the plate. Stem cells are in the neural crest. Some remain there and divide to form new stem cells, others migrate away and become neurons or glia. The neural tube sinks beneath the epidermal cells.
What develops first?
The axon.
The dendrites typically develop when…
the cell reaches its destination.
What is the chemoaffinity hypothesis of synaptogenesis?
Neurons find specific target locations and are guided by chemical gradients.
What did Sperry do?
Cut the optic nerve of a newt and rotated the eye 180 degrees (put it upside-down) - neurons return to original targets despite being flipped.
What evidence is there that neurogenesis occurs in adult mammals?
Stem cells persist in some areas of adult human brians. First discovered in the olfactory bulb. Stem cells divide indefinitely. One of those cells can form a sensory neuron to replace others that die in the olfactory bulb. Stem cells ALSO in hippocampus - memory! neurogenesis here my help to enhance memory.
What are the implications of synaptic elimination in brain development?
(less is more?) - look at text.
If you cut off a finger of a rhesus monkey…
the region of the brain that used to represent that finger begins to represent the remaining adjacent fingers.
Extensive practice of movement results in an…
increased volume of brain that represents that movement.`
What do genes do?
They create proteins.
What do proteins do?
They’re like little machines that allow cells to work.
What are complex proteins made of?
A long string of amino acids that then fold in complex ways.
Where is the DNA contained within a cell?
The nucleus.
What is another word for nucleotides?
Bases.
What is the importance of the bases?
The order/sequence of the bases (like a code) conveys information that represents amino acids.
What are DNA strands wrapped around to shorten the length?
Histones. This shortens the length of DNA strands by around 40,000x.
Where are the chromasomes?
Within the nucleus of the cell.
How many chromosomes are in the nucleus of the cell?
46 chromosomes.
What determines one amino acid?
A triplet of bases.
What is RNA?
It is a copy of one strand of the DNA.
What is an enzyme?
Biological catalysts that regulate chemical reactions in the body.
What type of effect does a dominant gene show in either homozygous or heterozygous presentation?
It shows a strong effect.
What type of effect does a recessive gene show in either homozygous or heterozygous presentation?
It only shows its effect in a homozygous (matching pair) presentation.
What is the effect of chemicals in a cell’s environment on DNA expression via histones?
Epigenetics.
What happens to histones when we consider epigenetics?
The histones will change their shape, and the DNA wrapped around it will be loosened up, unzipped, accessed via RNA and proteins made via ribosomes.
by what stage is the forebrain, midbrain and hindbrain distinctly developed prenatally?
7 weeks.
When does the CNS begin to develop?
around 2 weeks.
What does the neural plate (at around 18 days) develop into?
Almost all tissue required for the nervous system. All neurons and glia.
What happens to the neural plate?
It invaginates. The neural crest (top) closes over the neural groove to make neural tube (around 21 days).
What occurs at the Proliferation stage?
Cells (stem cells) in ventricles (neural crest/groove) divide. Some become primitive neurons and glia, can develop into any type of mature neuron.
What occurs during Migration?
cells follow chemical path (via chemical gradients) toward final destination. These chemicals are on the surface of cells in different concentrations. These chemicals are Immunoglobulins and chemokines.
Axons may begin to develop, and be fully developed before arriving at destination.
What are the particular chemicals used by cells migrating toward final destination?
Immunoglobulins and chemokines.
Does proliferation stop once migration begins?
No, there’s overlap, especially in early stages.
What occurs during Differentiation?
While neuron is still migrating, different genes active in different types of neuron. Dendrites will develop when it reaches destination.
What happens during Myelenation?
addition of insulating sheath that speeds transmission (still forming up to 20+ years of age).
When does Myelenation occur?
Once cells have finished differentiating.
What happens during Synaptogenesis?
The formation of synapses and dendritic branches continues throughout life. Most synapses are done before myelenation is finished (around 20 years of age).
What are the determinants of neuronal survival?
- Must form synpse with target cell and receive a nerve growth factor (a neurotrophin) from that cell PNS
- Must ALSO be stimulated to relesase neurotransmitters into synapses CNS.
What did Sperry cutting up some optic nerves tell us about the Chemoaffinity hypothesis?
Axons regrew after cutting the optic nerves. Axons went out of their way to go back to their original place of connection, targeting particular chemicals.
How does synaptic elimination work?
Neurons “try out” new synapses.
- if synapse contributes to a useful neural circuit then it remains
- if not, then the synapse is lost
Why do brains, despite not gaining neurons, accrue more mass up to adulthood?
Dendrite/axon growth + myelenation.
What happens if there is a change in circumstances, regarding synapses?
Synapses that weren’t useful may become useful.
If the synapse contributes to a useful neural circuit, it remains.
The amount of cortex ‘representing’ a function can increase.
Which genes are Sex-linked genes?
Those found on the sex chromosomes.
Which genes are the autosomal genes?
those found on all other chromosomes other than the sex chromosomes.
What are sex-limited genes?
Genes that only become active in one sex and not the other, controlled by epigenetics (histones)/hormones.
What are the 3 RNA bases refered to as?
A Codon, which represent a specific amino acid.
