unit 3: cells, traits and cells of the nervous system Flashcards
synapse
basic input-output unit for transmission of information
macromolecules
organized to form the synapse, different types of macromolecules underlie the generation of impulse and other active properties involved in information processing
mendel’s observations
The genetic determinants are particulate; they don’t blend and they assort independently. He called the determinants elementen. Only much late was elementen called a gene
He concluded that each individual plant has two copies of elementen
Although all somatic cells have two copies of each allele, only one allele is passed on to an offspring from a female and one from a male in the form of a gamete in sexual reproduction
law of dominance
parents that are pure for contrasting traits, only one form of the trait will appear in the next generation
law of segregation
during the formation of gametes, the two alleles responsible for a trait separate from each other. alleles for a trait are then “recombined” at fertilization, producing the genotype for the traits of the offspring
allosteric proteins
many proteins change their shape upon binding a ligand
protein phosphorylation
post-translational modification of proteins in which certain amino acids in the chain of amino acids is phosphorylated by a protein kinase by the addition of a phosphate group allosteric proteins
- alters the shape of a protein, causing it to become activated, deactivate or modifying its function
dephosphorylation is catalyzed by
protein phosphatases
most commonly phosphorylated
serine, theonine, and tyrosine in eukaryotes
phosphorylation by ATP can activate an allosteric protein
Phosphorylation by ATP can activate an allosteric protein. In this example the inactive conformation of the non phosphorylated protein (A) is favored 1000 to 1 because of a free energy difference of 4.3 kcal/mole. When phosphorylated, the active conformation of the protein (B) is favored 100 to 1 (2.8 kcal/mole) because the phosphorylation produces an unfavorable charge repulsion, part of which is relieved by a shift to the active conformation C*. In this way phosphorylation “pushes” the enzyme into the active conformation. Alternatively, phosphorylation could create a charge attraction that brings together two separated parts of an allosteric protein.
generating mRNA from DNA
An enzyme (RNA polymerase) travels along DNA, making a messenger RNA (mRNA) transcript by adding nucleotides one at a time, copying the oligonucleotide sequence from one of the DNA strands. The strand of DNA used as the template for the RNA strand is called the sense strand. RNA is made only from one of the two DNA strands. The strand that is not transcribed into mRNA is called the antisense strand.
base pairing and hybridization
- Hybridization is the process of combining two complementary single-stranded DNA or RNA molecules and allowing them to form a single double-stranded molecule through base pairing. In a reversal of this process, a double-stranded DNA (or RNA, or DNA/RNA) molecule can be heated to break the base pairing and separate the two strands. Hybridization is a part of many important laboratory techniques such as polymerase chain reaction (PCR) and Southern blotting.
the process of generating a peptide from mRNA
The nucleotides in an mRNA molecule are joined together to form a complementary copy of a segment of one strand of DNA. They are then matched three at a time to complementary sets of three nucleotides in the anticodon regions of transfer RNA (tRNA) molecules. At the other end of each type of tRNA molecule, a specific amino acid is held in a high-energy linkage, and when matching occurs, this amino acid is added to the end of the growing polypeptide chain. Thus, translation of the mRNA nucleotide sequence into an amino acid sequence depends on complementary base-pairing between codons in the mRNA and corresponding tRNA anticodons. The molecular basis of information transfer in translation is therefore very similar to that in DNA replication and transcription. Note that the mRNA is both synthesized and translated starting from its 5’ end.
The genetic code consists of sequences of three bases (codons) that are laid out along a strand of mRNA.
Another form of RNA, transfer RNA (tRNA), carries specific amino acids to their “docking sites” so that the amino acids are in close proximity to one another.
An enzyme causes the formation of a peptide bond and the new amino acid is attached to its predecessor.
a series of ribosomes simultaneously translate the same RNA molecule
Ribosomes are the organelles in the cytoplasm on which mRNA is translated into proteins. Ribosomes themselves are RNA molecules (i.e., ribosomal RNA; rRNA). For each polypeptide chain being synthesized from an mRNA molecule in a eukaryotic cell, protein synthesis begins with the binding of a small ribosomal subunit to the single appropriate site on the mRNA molecule and proceeds from the 5’ end to the 3’ end of the mRNA chain. When a polypeptide chain is completed, the two ribosomal subunits dissociate from the mRNA.
protein synthesis
The nuclear envelope keeps functional ribosomes out of the nucleus, so that RNA transcripts can be extensively processed (spliced) before they are transported out of the nucleus into the cytoplasm, where they are translated into proteins by ribosomes. Thus, RNA processing and transport steps are interposed between DNA transcription and RNA translation.
This figure shows the movement of mRNA out of the nucleus, into the cytoplasm, the attachment of ribosomes, and finally the attachment of the ribosomes to the endoplasmic reticulum (ER) where, in this particular case, the protein is made.
This figure also illustrates how a protein formed in the rough ER moves through the smooth ER to the Golgi apparatus where the protein is “packaged” in granules.
In the case of neurons, these secretory granules may contain neurotransmitters or enzymes involved in transmitter synthesis.
The transmitter or transmitter enzyme is transported down the axon to the nerve termina
phenylketonuria
If undetected and untreated, PKU leads to a profound intellectual disability.
Affects 1 in 5,000 newborns in Western Europe
Autosomal recessive trait
The heterozygous trait is rather common (2%).
Therefore, 2 heterozygous parents have a 1 in 4 chance of having a child with PKU.
PKU can be detected at birth (Guthrie Test).
Treatment is feeding a diet low in phenylalanine and rich in tyrosine.
Phenylalanine hydroxylase gene (PKU) mapped on human chromosome 12q24.1
Phenylalanine accumulates in the blood because of a block in conversion to tyrosine (lack of phenylalanine hydroxylase).
conversion of phenylalanine to tyrosine
The chemical structures and co-factors can be disregarded. However, the reaction of conversion of phenylalanine to tyrosine by phenylalanine hydroxylase is the first step in the synthesis of catecholamines (dopamine, norepinephrine, and epinephrine), a metabolic cascade with which you should be eventually familiar.
thomas hunt morgan
- columbia university
- founder of modern experimental genetics
- chromosomal theory of hereditary
- drosophila melanogaster
- 1933 nobel prize
archibald garrod
british physician
- 1909 recognized that the disease alkaptonuria was caused by a rare recessive gene mutation inherited according to mendelian rules
- “inborn errors of metabolism” surmised the nature of the genetic defect
- “we may further conceive that the splitting of the benzene ring in normal metabolism is the work a special enzyme, that in congenital alkaptonuria this enzyme is wanting”
alkaptonuria
was caused by a recessive gene mutation inherited according to mendelian rules
- characterized by the accumulation of homogentisic acid in the body. affected individuals lack enough functional levels of an enzyme required to breakdown homegentisic acid
george w beadle
1958 nobel prize
- neurospora crassa (bread mold)
- normal spores require only water, sugar, ammonium salt, and biotin
- 1 in 1000 required an enriched medium of a single added substance such as a vitamin or amino acid to restore growth
- they concluded that the mutant cells carried a defect in a single gene that impaired the production of an enzyme for a single metabolic step
- that is: one gene was responsible for one enzyme
