20.4 - Information Flow in Biological Systems Flashcards
central dogma
in cells the flow of genetic information contained in DNA is a one-way street that leads from DNA to RNA to protein
The process by which a single strand of DNA serves as a template for the synthesis of an RNA molecule is called
transcription
The process by which the message is converted into protein is called
translation
Unlike transcription, the process of translation involves converting the information from
one language to another
In this case, the genetic information in the linear _________ is being translated into a protein, a linear ________
sequence of nucleotides
sequence of amino acids.
Three classes of RNA molecules are produced by transcription
messenger RNA, transfer RNA, and ribosomal RNA.
Messenger RNA (mRNA)
carries the genetic information for a protein from DNA to the ribosomes. It is a complementary RNA copy of a gene on the DNA.
Ribosomal RNA (rRNA)
a structural and functional component of the ribosomes, which are “platforms” on which protein synthesis occurs. There are three types of rRNA molecules in bacterial ribosomes and four in the ribosomes of eukaryotes.
Transfer RNA (tRNA)
translates the genetic code of the mRNA into the primary sequence of amino acids in the protein.
secondary and tertiary structures of tRNA
cloverleaf-shaped secondary structure resulting from base pair hydrogen bonding (A─U and G─C) and a roughly L-shaped tertiary structure
The sequence CCA is found at the 3′ end of the tRNA. The 3′-OH group of the terminal nucleotide, adenosine, can be
covalently attached to an amino acid
Three nucleotides at the base of the cloverleaf structure form the
anticodon
the anticodon, this triplet of bases forms hydrogen bonds to a
codon
codon
complementary sequence of bases on a messenger RNA (mRNA) molecule on the surface of a ribosome during protein synthesis.
This hydrogen bonding of codon and anticodon brings the
correct amino acid to the site of protein synthesis at the appropriate location in the growing peptide chain.
transcription is catalyzed by
the enzyme RNA polymerase
transcription occurs in 3 stages
initiation
elongation/synthesis of the RNA transcript
termination
initiation
involves binding of RNA polymerase to a specific nucleotide sequence, the promoter, at the beginning of a gene.
This interaction of RNA polymerase with specific promoter DNA sequences allows RNA polymerase to recognize
the start point for transcription.
and also determines which DNA strand will be transcribed
Unlike DNA replication, transcription produces a
complementary copy of only one of the two strands of DNA.
As it binds to the DNA, RNA polymerase separates the two strands of DNA so that it can
“read” the base sequence of the DNA.
chain elongation
begins as the RNA polymerase “reads” the DNA template strand and catalyzes the polymerization of a complementary RNA copy.
With each step, RNA polymerase transfers a _______to the end of the growing RNA chain and catalyzes the formation of a _______ bond between the_________group of the incoming ribonucleotide and the_______ group of the last ribonucleotide of the growing RNA chain.
complementary ribonucleotide
3′–5′ phosphodiester
5′-phosphoryl
3′-hydroxyl
The final stage of transcription is
termination
The RNA polymerase finds a ______sequence at the end of the gene and _____the newly formed RNA molecule.
termination
releases
In eukaryotes, transcription produces a
primary transcript that must undergo extensive post-transcriptional modification before it is exported out of the nucleus for translation in the cytoplasm.
Eukaryotic primary transcripts undergo three post-transcriptional modifications.
These are the addition of a 5′ cap structure and a 3′ poly(A) tail, and RNA splicing.
In the first modification, a ___ structure is ____ added to the__′ end of the primary transcript.
cap
enzymatically
5
The cap structure consists of
7-methylguanosine attached to the 5′ end of the RNA by a 5′–5′ triphosphate bridge.
The first two nucleotides of the mRNA are also
methylated
The cap structure is required for
efficient translation of the final mature mRNA.
The second modification is the enzymatic addition of a
poly(A) tail to the 3′ end of the transcript
Poly(A) polymerase uses ___ and catalyzes the stepwise polymerization of 100–200 adenosine nucleotides on the______
ATP
3′ end of the RNA.
The _____ protects the 3′ end of the mRNA from enzymatic degradation and thus _________
poly(A) tail
prolongs the lifetime of the mRNA.
The third modification
RNA splicing
RNA splicing
involves the removal of portions of the primary transcript that are not protein coding.
These sequences that do not code for proteins are called
intervening sequences or introns.
The primary transcript contains both
the introns and the protein-coding sequences, called exons.
The presence of introns in the mRNA would make it ____ for the process of translation to synthesize the ____ protein. Therefore, they must be removed, which is done by the process of ____
impossible
correct
RNA splicing
As you can imagine, RNA splicing must be very precise. If too much, or too little, RNA is removed, the mRNA will
not carry the correct code for the protein.
there are “signals” in the DNA to mark the boundaries of the
introns
The sequence ____ is always found at the intron’s 5′ boundary and the sequence ___ is found at the 3′ boundary.
GpU
ApG
Recognition of the splice boundaries and stabilization of the splicing complex requires the assistance of particles called
spliceosomes
Spliceosomes are composed of a variety of
small nuclear ribonucleoproteins (snRNPs, read “snurps”).
Each snRNP consists of a
small RNA and associated proteins.
The ____ components of different _____ are complementary to different sequences involved in ____
RNA
snRNPs
splicing
By hydrogen bonding to a splice boundary or intron sequences, the snRNPs
recognize and bring together the sequences involved in the splicing reactions.
it is the small RNA molecules that
catalyze the splicing reactions. Such catalytic RNAs are called ribozymes.
