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44 Cards in this Set

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  • Back
What do proteins control?
the shape, function, and chemical reactions of cells
Beadle and Tatum
1940s: worked with bread mold (Neurospora) and proposed the "One gene, one enzyme" theory
-they used two mutant strains of mold
MUTANT A-had a defect in enzyme that convertes citrulline to agrnine
MUTANT B- had a defect in enyzme that converted ornithine to citruilline
What is the normal biochemical pathway for Neurospora to make arginine?
| (Enzyme 1)
| (Enzyme 2)
"One gene, one protein" theory
Beadle adn Tatum found that a mutation in a specific gene disrupts the synthese of a specific enzyme
-sometimes genes code for nucleic acids
-sometimes genes have directions for more than one protein
Where is DNA found?
only in nucleus and sometimes in mitochondria(mitochondrial DNA)
-single strand
-found in the nucleus and the cytoplasm
-RNA nucleotides consist of:
*phosphate group (PO4)-
*nitrogen bases A, C, G, Uracil
messenger RNA
carries the protein-making code from the gene (made of DNA molecules in the nucleus) out into the cytoplasm (through nuclear pores), and then binds to a ribosome
transfer RNA
carries amino acids to the ribosomes. each transfer RNA molecule has three exposed bases (anticodon "AUG")
ribosomal RNA
combines with protein to make ribosomes(site of protein synthesis). helps trap the mRNA molecules and direct themn to ribosome
recently discovered
Protein Synthesis
STEP ONE-Transcription "to copy"
Info from DNA (in nucleus) is copied into RNA. RNA is synthesized.
STEP TWO-Translation(from language of nucleic acids -DNA&RNA to language of proteins)
RNA and ribosomes work together to make a specific amino acid sequence for a protein
How many nucleotide bases are need for transcription/translation? Why?
Three are needed because that creates 64 codes, while only using 2 bases creates 16 codes.
64 codes is more than enough codes for 20-21 amino acids
3 nucleotides that designate or specify a certain amino acid
ex. AAC
Start codon
AUG(codes for methionine)
all proteins start with this amino acid
Stop codon
UAG, UAA, UGA (these codons do not code for any amino acids)
they cause ribosome to release the protein
from DNA in nucleus to RNA in cytoplasm
-first the DNA helix must be spilt apart by enzyme
3 steps:
TRANSCRIPTION - - Initiation
RNA polymerase locates the promoter(site or region on the gene with a repeat) ex. TATATA...

RNA polymerase binds to it

DNA double helix unwinds at starting point of gene
TRANSCRIPTION - - Elongation
RNA polymerase moves along template single strand of DNA, pairing bases complemetnary to DNA (using A,C,G,U)

This action forms a single strand of RNA
RNA strand of 10+ nucleotides separate from DNA
TRANSCRIPTION - - Termination
When RNA polymerase reaches a termination signal on DNA, it stops

RNA molecule is released

RNA polymerase is also released to make one RNA

DNA rewinds mRNA molecule nucleus and goes to ribosomes in cytoplasm
How many genes do body cells have?
*not all genes are needed by each cell
ex. muscle cell-need the genes that code for actin and myosin
pancreatic cell-need the grene that codes for insulin
red blood cell-hemoglobin
Conrol Region
area on DNA molecule, near promoter site

proteins bind here: they may either block or allow RNA polymerase to bind
How many strands of DNA codes for a certain protein?
Only one

other side may be useless: "antisense DNA"antisense DNA" or other side may code for another protein
TRANSLATION -- Initiation
-mRNa codon AUG signals the start of translation
-an "initiation complex"(small ribosomal unit, plus a tRNA carrying methionine) is assembled
-inititation complex binds to mRNA (mRNA codon=AUG:pairs with tRNA anticodon (UAC)
-large ribosomoal subunit binds to smaller one, and tRNA binds to the larger unit
-mRNA is held in place between the 2 ribosomal subunits
TRANSLATION -- Elongation
-a ribosome can hold 2 mRNA codons at a time
-another tRNA anticodon arrives at the ribosome and pairs with a second mRNA codon (GUU)
-tRNA binds to 2nd tRNA site on large ribosomal unit
-2 a.a.'s side by side
-cataltic site on large ribosomal subunit breaks the bond between methionine and tRNA-forms peptide bond
-ribosome moves down the mRNA, new tRNA arrices, 2nd tRNA shifts on the ribosome
-new peptide bond forms
peptide bond
any amino acid bonded to another amino acid
TRANSLATION -- termination
-stop codon in mRNA signals ribosome to stop protein synthesis
-special proteins bind to the ribosome causing the protein to release protein chain
-ribosome subunits separate
-protein (100-200 a.a. long) can be synthesized in under 1 minute! (up to 15 peptide bonds per second!)
Gene mutation
defective gene due to changes in sequence of bases in DNA
How might mutations occur?
1. error in base pairing- during DNA replication (prior to cell division)
2. spontaneous base change-movement of atoms in DNA molecule
3. chemicals and radiation(UV)-increase chances of error in base pairing
Point mutation
one nucleotide in sequence is changed
nucleotide substitution
during enyzme repair of DNA, a correct nucleotide is accidentally replaced by an incorrect one
T G C C A A<--
insertion mutation
one or more new nucleotide pairs are inserted into DNA of gene
A C G G T A<--
deletion mutation
one or more nucleotide pairs are removed from gene
T A C C xGx A T =
Why are mutations beneficial in evolution?
may give an organism better characteristics - better chance for survival
How often do random mutations occur?
1/100,000 to 1/1,000 gametes (egg and sperm)
Effects of mutations in DNA on protein syntheis
1. Protein may remain unchanged. (Since a.a.s have more than one correct codon, some chanes in a single nucleotide have no effect)
mRNAGAG-->GAA Both code for gultamic acid
2. Protein may change, but be equvalent to the original
glutamic acid to glutamine-both a.a.s are hydrophilic-so protein will still function the same way
3. Protein function may be changed
glutamic acid-->valine (noth hydrophobic)
4. Protein function may be stopped
Ex. CTC-->ATC(a stop codon)
protein is not completely synthesized
1. cells control the frequency of gene transcription; type of cell determines if gene is transcribed & how much protein is needed (in eukaryotic cells much of the DNA in a gene does not code for any proein, so after the gene is transcribed, the unneeded info must be removed)
2. mRNA molecules vary:-some mRNA is very stable, long-lasting(can be translated into protein many times)-some mRNA degrades easily(it can only be used a few times)-some cells block the trnalsation of certain mRNA until another metabolic signal allows it to occur
3. some proteins must be modified before they can function properly ex. digestive enyzme may be inactive in the pancrease, but may become activated in the intestines (due to pH chance), so the enzyme won't digest the pancreas
4. protein life span can be regulated-cells can chemically prevent protein degradation & cells can chemically promote protien degradation
non-coding segments of DNA that are removed
they intervene between coding segments in DNA
segments of DNA that code for protein, therefore: they are expressed
regulatory proteins
bind to the promoter site on a gene, making it easier for RNA polymerase to bind to the promoter and start transcription to mRNA
ex. (in the endocrine system)-a lipid-soluble protein enters cells, binds to receptor, enters nucleus, binds to DNA
Why are certain regions of the chromosome condensed?
so RNA polymerase can't get to it
so-DNA will not accidentally be copied when not needed
when protein is needed gene becomes "uncondensed"-thread-like
Barr Bodies
one of the X chromosomes in cells of a female becomes tightly condensed into a mass
-this occurs because males only have one X chromosome, so this helps to equalize the amount of genetic material in each gender
Calico cat
in some female cells, one X chromosome is condensed, and in other cells, another X chromosome is condensed
-different X chromosomes carry genes for different colored fur0so some cells make black-pigmented fur (X chromosome for orange fur was condensed). some cells make orange pigment fur (X chromosome for black fur was condensed)
Androgen insensiticity
caused by a change in the nucleotide sequence of a single gene(SRY) which then causes a single defective protein to be produced. the defective protein is an androgen receptor protein. the androgen receptor protein binds to male hormones (ex. testosterone) forms HRC (hormone-receptor complex). the HRC binds to ceratin areas on a gene, causing DNA to be copied by mRNA. These genes control "maleness"->testes, hair, muscle
Werner syndrome
caused by a mutation in a gene that codes for an enzyme involved in DNA replication. a mutation on chromosome #8 causes promlem with enzymes that copy DNA, proofrean, repair DNA (helicase). too many mutations occur too rapidly in many body organs & causes you to age