Ch 10 From DNA to Proteins Flashcards
ribosomal RNA (rRNA)
along with ribosomal protein subunits, makes up the ribosome
messenger RNA (mRNA)
carries the coding instructions for polypeptide chains from DNA to the ribosome
pre-messenger RNAs (pre-mRNAs)
large precursor molecules; are the immediate products of transcription in eukaryotic cells
not found in bacterial cells
transfer RNA (tRNA)
serves as the link between the coding sequence of nucleotides in an mRNA molecule and the amino acid sequence of a polypeptide chain
small nuclear RNAs (snRNAs)
combine with small protein subunits to form small nuclear ribonucleoproteins (snRNPs)
small nucleolar RNAs (snoRNAs)
takes part in the processing of rRNA
microRNAs (miRNAs) and small interfering RNAs (siRNAs)
two types of very small and abundant RNA molecules found in the cytoplasm of eukaryotic cells
RNA interference (RNAi)
a process in which these small RNA molecules help trigger the degradation of mRNA or inhibit its translation into protein
three major components of transcription
1) A DNA template
2) The raw materials (ribonucleotide triphosphates) needed to build a new RNA molecule
3) The transcription apparatus, consisting of the proteins necessary for catalyzing the synthesis of RNA
template strand
the nucleotide strand used for transcription
nontemplate strand
not ordinarily transcribed
transcription unit
a stretch of DNA that encodes an RNA molecule and the sequences necessary for its transcription
promoter
a DNA sequence that the transcription apparatus recognizes and binds
indicates which of the two DNA strands is to be read as the template and the direction of transcription
RNA-coding region
a sequence of DNA nucleotides that is copied into an RNA molecule
three critical regions within a transcription unit
a promoter, an RNA-coding sequence, and a terminator
terminator
a sequence of nucleotides that signals where transcription is to end
ribonucleoside triphosphates
RNA is synthesized from this
RNA polymerase
carries out all the required steps of transcription
core enzyme
five subunits (individual polypeptide chains) make up this enzyme catalyzes the elongation of the RNA molecule by the addition of RNA nucleotides
sigma factor
controls the binding of RNA polymerase to the promoter
holoenzyme
sigma factor associates with the core enzyme
consensus sequences
short stretches of common nucleotides; they possess considerable similarity, or consensus
10 consensus sequence
sometimes called the Pribnow box
written simply as TATAAT
35 consensus sequence
sequence common to most bacterial promoters is TTGACA, which lies approximately 35 nucleotides upstream of the start site
Rho-dependent terminators
able to cause the termination of transcription only in the presence of an ancillary protein called the rho factor
Rho-independent terminators
also known as intrinsic terminators
able to cause the end of transcription in the absence of rho
rho utilization site (rut)
serves as a binding site for the rho protein, which binds the RNA and moves toward its 3’ end, following the RNA polymerase
hairpin
inverted repeats (sequences of nucleotides on the same strand that are inverted and complementary) are transcribed into RNA and bind to each other, forms this secondary structure
polycistronic RNA
produced when a single terminator is present at the end of a group of several genes that are transcribed together, instead of each gene having its owen terminator
exons
- many eukaryotic genes contain these coding regions
- are joined to yield the mature RNA
introns
noncoding regions called intervening sequences
common in eukaryotic genes but are rare in bacterial genes
tend to be longer than exons
do not encode proteins
codon
in mRNA, each amino acid in a protein is specified by a set of three nucleotides
three primary regions of prokaryotic and eukaryotic mRNAs
5’ untranslated region, the protein-coding region, and the 3’ untranslated region
5’ untranslated region
5’ UTR, sometimes called the leader
a sequence of nucleotides at the 5’ end of the mRNA, does not encode any of the amino acids of a protein
Shine-Dalgarno sequence
a consensus sequence (UAAGGAGGU) which serves as the ribosome-binding site during translation
found approximately seven nucleotides upstream of the first codon translated into an amino acid (the start codon)
protein-coding region
comprises the codons that specify the amino acid sequence of the protein
begins with a start codon and ends with a stop codon
5’ untranslated region
3’ UTR, sometimes called a trailer
a sequence of nucleotides that is at the 3’ end of the mRNA and is not translated into protein
5’ cap
cap consists of an extra modified nucleotide at the 5’ end of the mRNA as well as methyl groups (CH3) on the 2’-OH group of the sugar of one or more nucleotides at the 5’ end
poly(A) tail
addition of 50-250 or more adenine nucleotides at the 3’ end; these nucleotides are not encoded in the DNA, but are added after transcription in a process termed polyadenylation
RNA splicing
removal of introns
takes places in the nucleus, before the RNA moves to the cytoplasm
5’ splice site and 3’ splice site
these splice sites possess short consensus sequences
branch point
an adenine nucleotide that lies from 18 to 40 nucleotides upstream of the 3’ splice site
spliceosome
splicing takes place within a large structure which is one of the largest and most complex of all molecular structures
lariat
pre-mRNA is cut at the 5’ splice site which frees exon 1 from the intron, and the 5’ end of the intron attaches to the branch point; that is, the intron folds back on itself
alternative processing
many eukaryotic mRNAs undergo this which is a single pre-mRNA is processed in different ways to produce alternative types of mRNA, resulting in the production of different proteins from the same DNA sequence
alternative splicing
the same pre-mRNA can be spliced in more than one way to yield multiple mRNAs that are translated into different amino acid sequences and thus different proteins
cloverleaf structure
some of the nucleotides in a tRNA are complementary to each other and form intramolecular hydrogen bonds which results in this
anticodon
a set of three nucleotides which pairs with the corresponding codon on the mRNA during protein synthesis to ensure that the amino acids link in the correct order
trimming
additional nucleotides may then be removed one at a time from the 5’ and 3’ ends of the tRNA in a process known as this
two subunits of a functional ribosome
large ribosomal subunit and small ribosomal subunit
RNA interference (RNAi)
a powerful and precise mechanism used by eukaryotic cells to limit the invasion of foreign genes (from viruses and transposons) and to censor the expression of their own genes
triggered by double-stranded RNA molecules, which may arise in several ways: by the transcription of inverted repeats into an RNA molecule that then base pairs with itself to form double-stranded RNA; by the simultaneous transcription of two different RNA molecules that are complementary to one another and that pair, forming double-stranded RNA; or by infection by viruses that make double-stranded RNA
two abundant classes of RNA molecules that function in RNA
small interfering RNA and microRNAs
RNA-induced silencing complex (RISC)
both siRNA and miRNA molecules combine with proteins to form this
the key to functioning of RISCs is a protein called Argonaute
CRISPR RNAs
Assist in the destruction of foreign DNA molecules
