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RNA is ____ from DNA
transcribed
RNA is __________ into protein
translated
How do genes direct the synthesis of proteins?
transcription and translation
Where does transcription occur?
the nucleus
Where does translation occur?
the cytoplasm
______ in the link between DNA and protein
RNA
What are the components of RNA?
1 ribose, a phosphate group, and a nucleotide base
RNA typically function as ______________ but can bind to themselves to provide 3D structure
single-stranded polymers
What are the 3 types of RNA involved in protein synthesis?
mRNA, tRNA, rRNA
What is the function of mRNA?
provides the genetic instructions to make proteins
What is the function of tRNA?
carry amino acids to ribosomes on one end and bind mRNA on the other end
What is the function of rRNA?
form the body of the ribosome and provide a physical link between mRNA and tRNA
What happens in transcription?
DNA of one gene unwinds
RNA polymerase transcribes a copy of DNA into RNA
Codon is read and translated into amino acids and proteins in the ribosome
What enzyme translates a copy of DNA into RNA?
RNA polymerase
A specific sequence of three adjacent bases on a strand of DNA or RNA that provides genetic code information for a particular amino acid
codon
RNA polymerase binds to a promoter, where the helix unwinds and transcription starts
initiation
RNA polymerase moves 5' to 3', unwinding the DNA and elongating the RNA transcript
elongation
RNA polymerase reaches a terminator sequence and detaches from the template, separating RNA and DNA
termination
What are the three stages of transcription?
initiation, elongation, termination
mRNA is complementary to the _____________
template strand of DNA
What are attached to the end of mRNA in processing?
5' guanine cap and poly-A tail
What is the function of the 5' cap and poly-A tail?
to protect the RNA and help it to exit the nucleus safely
What makes up the poly-A tail?
50-250 adenine nucleotides
What happens in RNA splicing?
introns are cut out and eons are spliced together
The ________ complex of proteins and RNAs helps splice RNA
spliceosome
What must occur before the mRNA can leave the nucleus?
Processing and Splicing
What is the product of translation?
a protein
How many start codons are there?
1
How many stop codons are there?
3
How many possible codons are there?
64
What are the two main features of the genetic code?
universal and redundant
What is the Wobble Hypothesis?
There is some wiggle room in the 3rd nucleotide in a codon, allowing many codons to code for the same amino acid if they have the same first 2 bases
A tRNA contains ___ base-paired regions
4
Where does the amino acid bind to the tRNA?
3' end
group of three bases on a tRNA molecule that are complementary to an mRNA codon
anticodon
When is a tRNA charged?
when an amino acid is attached
How is tRNA activated?
The active site binds an amino acid and ATP, ATP loses 2 phosphates and joins amino acids as AMP, appropriate tRNA binds to amino acid, displacing AMP, then the activated amino acid and AMP is released by the enzyme
What enzyme helps activate tRNA?
aminocyl-tRNA synthetases
structure made of rRNA and proteins
ribonucleoprotein
eukaryotic ribosomes are ________ than prokaryotic ribosomes
bigger
When does tRNA fit into a binding site on a ribosome?
its anticodon is base-paired with an mRNA codon
what are the 3 sites in a ribosome?
A, P, E
What is the function of the A site?
holds incoming activated tRNA
what is the function of the P site?
holds the tRNA that carries the growing polypeptide chain
What is the function of the E site?
Holds un-activated tRNS
How is translation initiated?
Small ribosomal subunit binds to mRNA, large ribosomal subunit completes the initiation complex, charged tRNA binds to mRNA by complementary base-pairing and then the large subunit comes over the top to complete initiation
How many ribosomal subunits are there?
2
What are the stages of the elongation cycle?
Codon recognition, peptide bond formation, translocation
What happens during codon recognition?
a tRNA is recruited into the A site
What happens in peptide bond formation?
The enzyme peptidyltransferase detaches the aa at the P site and joins it to the aa at the A site
What happens in translocation?
The ribosome shifts down the mRNA, moving the protein chain into the P site
What signals the termination in translation?
The ribosome reaches a stop codon
Wehn translation is terminated a release factor promotes _____________, and uses ________
hydrolysis, 2 GTP
Why do polyribosomes form?
Because the half-life or mRNA is so short, many ribosomes cluster on the same mRNA at the same time so the many proteins can be made at the same time
What is the purpose of the signal peptide KDEL?
To be recognized by a signal recognition particle, which pulls the protein t the ER and threads it through the ER lumen
What is the difference in gene expression in prokaryotes and eukaryotes?
In prokaryotes polyribosomes stay attached to DNA via DNA polymerase. In eukaryotes ribosomes are in the cytoplasm. In prokaryotes transcription and translation occur simultaneously, and in eukaryotes mRNA processing occurs in between.
What type of mutation causes SCD?
point mutation
In sickle cell anemia hydrophobic --- is inserted instead of hydrophilic ----
valine, glutamic acid
3 Types of base-pair substitution
silent mutation, missense mutation, nonsense mutation
A mutation that changes a single nucleotide, but does not change the amino acid created.
silent mutation
A base-pair substitution that results in a codon that codes for a different amino acid.
missense mutation
A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.
nonsense mutation
What gene is a common example of a frameshift causing an immediate nonsense?
BRCA1
What diseases are associated with insertions causing missense?
Huntington's and Fragile X Syndrome
What disease is associated with the insertion or deletion of 3 nucleotides causing a missing or extra amino acid?
cystic fibrosis
What did Garrod discover?
inborn errors of metabolism
What scientists had the one-gene, one-enzyme hypothesis in the 1940s?
Beadle and Talum
Who won the Nobel Prize in 1954 for prosing a genetic relationship between sickle-cell hemoglobin and the sickle-cell trait?
Linus Pauling
Why do cells switch genes on and off?
to conserve resources
DNA unpacking involving histone acetylation and DNA demethylation
chromatin modification
Histone tails form a(n) ___________
Octomer
histone tails protrude outward from a ________
nucleosome
chromatin that is methylated is _______________
inactive
chromatin that is acetylated is ____________
active
a functional group containing a carbonyl and a methyl
acetyl group
Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence.
epigentic inheritance
The TATA box is a ___________
promoter
the binding site for RNA polymerase
TATA box/ promoter
What are proximal control elements needed for?
accurate transcription initiation
What do proximal control elements do?
bind the transcription initiation complex
What do distal control elements do?
Increase the rate of transcription
proteins that bind to enhancer sequences in eukaryotes to increase transcription
activator proteins
What brings the bound activators closer to the promoter?
DNA bending protein
Where do activators bind to other transcription factors?
the promoter
DNA that is densely packed around histones
Heterochromatin
loosely packed chromatin
euchromatin
What factors affect transcription during chromatin modification?
DNA methylation and acetylation, epigenetic regulation
What regulates the initiation of transcription?
DNA control elements in promoters and enhancers binding specific transcription factors
Cell type specific expression begins with the ____________
zygote
miRNA
Micro RNA
enzyme that cleaves and processes double stranded RNA to produce miRNAs
Dicer
An miRNA that is bound to proteins can base pair with ________________ that contains the complementary sequence
any target mRNA
What do miRNAs do?
block translation
A protein that attaches itself to faulty or misfolded proteins and thus targets them for destruction by proteasomes
ubiquitin
A giant protein complex that recognizes and destroys proteins tagged for elimination by the small protein ubiquitin.
proteasome
small infectious particle consisting of nucleic acid enclosed in a protein coat and sometimes a membranous envelope
virus
the protein shell that encloses the viral genome
capsoid
_______ use host cell materials to self-assemble
viruses
protein subunits that make up capsids
capsomeres
A virus that infects bacteria
Bacteriophage
Note
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