RNA and viruses Flashcards
What are ribozymes?
Enzymes that catalyze RNA cleavage
What are the key features of tRNA?
Cloverleaf structure
key features
– 3’ end covalently attached to
specific amino acid
– anti-codon loop – 3 nucleotides binds to codon in mRNA
– other loops for recognition – aa tRNA synthase, ribosome
What is the most abundant RNA? What are its features?
most abundant RNA – complex structure
3D structure is conserved, sequence is not
• component of ribosomes – 2 subunits, each
has several RNAs and 20-50 proteins
• rRNA is scaffold for proteins to bind
• catalytic activity of the
ribosome is in the rRNA
What is an ORF?
open reading frame (ORF) – part of the mRNA
coding for a protein
What are the characteristics of prokaryotic mRNAS?
prokaryotic mRNAs
– can be polycistronic – encode >1 protein
– not modified
– translated during or shortly after it is made
What are the characteristics of eukaryotic mRNAs?
eukaryotic mRNAs
– generally monocistronic
– extensively modified – including splicing
– transcribed in nucleus, translated in cytoplasm
What are miRNAs?
miRNA – microRNAs – 22-26 nucleotides
– gene expression regulation
– assemble into RISC complex – bind mRNA and block
translation
What are snoRNAs?
snoRNA – small nucleolar RNA – 70-300 nucleotides
– facilitate chemical modification of rRNA
– encoded with rRNA genes
– component of snoRNP – small nucleolar ribonucleoprotein
– snoRNA guides snRNP to correct site on rRNA via base
pairing
What are siRNAs?
siRNA – small interfering RNAs - 21-23 nucleotides
– bind mRNA and induce mRNA degradation
What are snRNAs?
snRNA - small nuclear RNAs – 100-300
nucleotides – called U1, U2, U4, U5, U6
– bind proteins to form snRNPs – small nuclear ribonucleoproteins
– involved in mRNA splicing – component of the spliceosome
What are lncRNAs?
lncRNA – long noncoding RNA
– long RNAs that do not encode proteins and play a role
in the regulation of gene expression
– e.g. Xist – a 17,000 – 20,000 nucleotide RNA that
functions in inactivation of the X chromosome
What is the difference between + and - ssRNA viruses?
+ve stranded – the viral genome is the same as mRNA
-ve stranded – the viral genome is complementary to mRNA
What happens when a virus hijacks a cell?
Virus infects a cell – hijacks cell machinery to make
more virus
– to make viral RNA
– to make viral protein
– to replicate genetic material
– to alter metabolism of the cell to favor viral production
What is the structure of a T4 phage?
viral anatomy
– head – capsid – contains ds DNA
– tail – attaches to host bacteria
What happens when a T4 phage infects a bacteria?
viral infection – DNA injected into bacteria – within minutes synthesis of bacterial DNA, RNA and protein STOPS – phage mRNA synthesis begins • virulent or lytic cycle – phage protein synthesis occurs • capsid proteins • enzymes for DNA replication • proteins to help assemble new phage • proteins to help the mature virus escape – replication of genetic material – assembly of new phage – bacterial lysis and release of the new phage
What is a temperate phage?
rather than making new phage, the phage genome
integrates into the host DNA
aka lysogenic
What is a prophage?
prophage – integrated phage genome
– prophage is replicated as part of the host DNA,
but does not produce RNA, proteins and genetic
material to make new phage
Where do eukaryotic cell-infecting viruses replicate?
Some in cytoplasm, some in nucleus
What are the features of Zika virus?
Zika virus is a ss +stranded RNA virus and it is enveloped
What important proteins are involved in Zika virus activity?
Capsid protein - binds RNA – assembles viral particle
• M protein – transmembrane protein
• E protein – transmembrane protein, receptor for the
cell – mediates membrane fusion
• Replicase complex – comprised of 5 nonstructural
proteins – has RNA-dependent RNA polymerase
What is the function of Zika E protein?
• E protein – transmembrane protein, receptor for the
cell – mediates membrane fusion
What are the steps in Zika infection?
1) virus attaches to cell surface receptor
2) endocytosis–virus enveloped in vesicle
3) vesicle pH lowers
4) viral envelope fuses with vesicle membrane, releasing capsid/genome
5) caspid is disassembled, viral genome translated, viruses produced
What are the steps in Zika viral genome expression?
1) existing +stranded ssRNA can be directly translated into mRNA
3) Replicase complex synthesizes second RNA strand complementary to +ssRNA, then uses it as template to synthesize many new copies of +ssRNA
Where does Zika viral replication occur?
Close to the ER
