Cell Biology Chapter 18 Flashcards
The principle of directional information flow from where?
DNA to RNA to protein; is the central dogma of molecular biology
What is a genetic code?
the relationship between the DNA base sequence and the linear order of amino acids in the protein products
The coded information of DNA is used to what? There are how many DNA bases and how many amino acids?
to guide production of RNA and protein molecules; 4 DNA bases, 20 amino acids
What is a triplet code and how many possible combinations are there? What is transcription?
combinations of 3 bases that specify amino acids; have 64 possible combinations more than enough for all 20 amino acids; synthesis of RNA molecule
DNA serves as a template for what? What does transcription refer to?
synthesis of an RNA molecule which then directs the synthesis of a protein product; refers to RNA synthesis using DNA as a template
What is translation? What is mRNA?
synthesis of protein using the information in the RNA; RNA that is translated into protein (only translated RNA)
What is rRNA? What is tRNA?
integral component of the ribosome; molecules serve as intermediaries, bringing amino acids to the ribosome (functional RNA)
Bacteria doesn’t have a what? TranslationofmRNAcanbeginbeforewhen?The compartmentalization of eukaryotic cells leads to what?
nuclear envelope, before its transcription is completed; spatial separation of transcription and translation
The gene is written how? Inserting or deleting a nucleotide causes what?
in a language of 3 letter word; the rest of the sequence to be read out of phase - this is a shift in the reading frame
What are frameshift mutations? There are 64 combinations of what and 20 combinations of what?
mutations that cause insertion or deletion of a nucleotide causing a shift on the reading frame; nucleotide triplets, amino acids
The genetic code is what and what is it’s definition? The genetic code is what and what is it’s definition? It is also what and what is it’s definition?
degenerate- a particular amino acid can be specified by more than 1 triplet; unambiguous- every codon has one meaning only; nonoverlapping- reading frame advances 3 nucleotides at a time
All 64 codon are used in what? 61 of them specify the addition of what? AUG role and UAA, UAG, UGA role? What else do codons do and not do
in the translation of mRNA; specific amino acids to a growing polypeptide chain; start a codon; stop a codon; terminate polypeptide synthesis and doesn’t code for any amino acid
In mRNA synthesis only what is copied? What is a template strand?
DNA strand; used as a template to make the mRNA
What is the coding strand?
The genetic information is the same as the mRNA; except that T in the DNA are U in the mRNA
RNA is chemically similar to what? It has a base of what? It is usually what?
DNA but contain ribose instead of deoxyribose; base of uracil instead of thymine; single stranded
Transcription begins when ?
when RNA polymerase binds to a promoter sequence triggering local unwinding of the double helix
RNA polymerase then initiates what? The mechanisms for initiation are different between what?
synthesis of RNA using one DNA strand as a template; prokaryotes and eukaryotes
The RNA polymerase moves along the what? What is a transcription bubble?
the DNA template unwinding the helix and elongating the RNA; unwound DNA
RNA polymerase dissociates from what?
DNA template leading to termination of synthesis and release of the RNA molecule
RNA polymerase binds to what and its definition?
DNA promoter site- a sequence of several dozen base pairs that determines where RNA synthesis will start
The terms what and what do they refer to? The promoter is what?
upstream and downstream refer to sequences located toward the 5’ or 3’ end of the transcription unit; upstream of the transcribed sequence
In bacteria a sigma subunit is key to what? What is a sigma factor?
initiate transcription; provides specificity for promoter recognition and it is needed to initiate transcription but dissociates shortly after initiation
Initiation of RNA synthesis takes place when? One of the DNA strands serve as a what?
once the DNA is unwound; a template for RNA synthesis
RNA polymerase uses what? RNA polymerase catalyzes what?
ribonucleoside triphosphate molecules that are complementary to the template strand; the formation of a phosphodiester bond between the NTPs
Chain elongation continues as what? RNA is elongated in which direction? As the polymerase moves along the DNA strand, the double helix ahead of the polymerase is what?
RNA polymerase moves along the DNA molecule; 5’ to 3’ direction with each new nucleotide added to the 3’ end; unwound and the DNA behind it is rewound into a double helix
Termination uses what? Intrinsic termination is what? These RNA molecules contain what?
specific sequences; most common termination in bacteria; contain a short GC-rich sequence followed by several U’s at the end of the transcript
The GC region in the RNA forms a what? Then the weaker bonds between the what of the template strand breakreleasingwhat?
hairpin loop pulling the RNA molecule away from the DNA; between the U’s and A’s break releasing RNA
Transcription in Eukaryotic Cells has what? RNA polymerase in eukaryotes requires what?
additional complexity compared with prokaryotes; additional proteins called transcription factors
The transcription factors do what? The RNA polymerase is able to do what?
recognize and bind the promoter; to bind the promoter
More transcription factors join what? RNA polymerase dissociates from what?
join after to trigger initiation; the transcription factors and carries out transcription
After initiation, RNA polymerases move along the what? For RNA polymerase 2, transcripts are cleaved at what?
the DNA and synthesize a complementary RNA; specific site before transcription ceases
The cleavage site is what? The cleavage site of polymerase 2 transcripts is also the site forwhat?
10-35 nucleotides downstream of AAUAAA sequence in the RNA; for addition of poly(A) tail
This is a string of adenine nucleotides added to what? RNA cleavage is more important than what?
the 3’ end of most eukaryotic mRNAs; termination of transcription
A newly produced RNA molecule is called what? It must undergo what before it can what? Eukaryotic transcripts must be exported form where?
primary transcript or pre-mRNA; RNA processing function in the cell; the nucleus to be translated
Substantial processing occurs where? Pre-mRNAs are processed by what? The C-terminal domain of one of the subunits of RNA polymerase 2 acts as what?
the nucleus before export; removal of sequences and addition of 5’ caps and 3’ tails; as a platform for protein complexes involved in processing
Eukaryotic mRNAs have a what? The 5’ cap is a guanosine that is methylated at it is bound to what?
modified nucleotide called the 5’ cap and the 3’ ends have a long stretch of adenines called the poly(A) tail; to the RNA molecule by 5’ -> 5’ triphosphate linkage rather than the usual 3’ -> 5’ bond
The 5’ cap is added when? The cap contributes to what?
soon after transcription is initiated; to mRNA stability by protecting the RNA from nucleases
The cap plays a role in what? The poly(A) tail is a string of what?
in positioning the RNA on the ribosome for initiation of translation; string of A nucleotides and is added by the enzyme poly (A) polymerase
A signal for addition of the poly(A) tail, AAUAAA, is located where? The poly(A) tail protects what from what?
just upstream of the polyadenylation site, and a GU- or U-rich element is located downstream from it; the mRNA from nuclease attack the length of the tail influences stability
Poly(A) tail is also required for export of the what? It may also help ribosomes how?
of the transcript to the cytoplasm; it may also help ribosomes recognize and bind mRNAs
What are exons? What are introns?
coding sequences that appear in the final mRNA; noncoding present in most protein-coding genes that separate the exons
What of introns varies considerably? What is RNA splicing?
the size and number; the process of removing introns and joining the exons
Sequences commonly found where determines what? The 5’ end of an intron typically starts with what and terminates with what?
at the intron-exon boundaries determine the 5’ and 3’ splice sites; starts with GU and terminates with AG at the 3’ end
What is branch point A? What is spliceosomes?
one additional sequence near the 3’ end of the intron; intron removal is catalyzed by large molecular complexes
The presence of intron allows what? What is alternative splicingispossibleviamechanismsallowingwhat?
allows each gene’s pre-mRNA molecule to be spliced in multiple ways, leading to production of multiple protein products; allowing certain splice sites to be activated or skipped
Many RNA processing events occur how? The long C-terminal domain (CTD) of RNA polymerase is responsible for what?
contranscriptionally; responsible for this processing
Many repeats of a seven-amino-acid sequence of the CTD bind enzymes needed for what?
capping, splicing, and cleavage/polydenlylation
