How Do genes Direct the Production of Proteins Flashcards
Cells achieve their specialized functions based upon (2)
the expression of specific genes and any subsequent post-translational modifications of the resulting proteins
DNA is — into RNA, which is — into Protein
transcribed
translated
in prokaryotes, when do transcription and translation occur?
simultaneously
is DNA or RNA more stable?
DNA is very stable, RNA degrades quickly as pH raises
RNA contains (2)
uracil
ribose sugar
DNA contains (2)
thymine
deoxyribose is missing an OH group
In both Prokaryotes and Eukaryotes only one strand of the DNA is transcribed into RNA depending upon the
gene
the RNA molecule being synthesized is made in the — direction and therefore the DNA strand that is used as template is oriented —
5’ to 3’
3’ to 5’
in both Prokaryotes and Eukaryotes gene transcription can proceed in opposite directions from
one gene to the next
In Prokaryotic organisms the DNA is organized in a linear or contiguous fashion and transcription of the DNA into RNA results in an RNA copy that is ready for use as a
template for protein synthesis (translation)
In Prokaryotic organisms the RNA transcript can be translated into a protein during the transcription process as there is
no nucleus
In Eukaryotic organisms the DNA is broken up into regions or blocks of sequence that will give rise to
the protein sequence (coding regions or exons)
These exons are separated by (2)
regions that do not code for protein (introns) and regions at the 5’ and 3’ ends that do not encode protein called untranslated regions (UTRs)
In Eukaryotic organisms one strand of the DNA is first copied in a linear fashion and then the introns are removed by a process called
splicing
Subsequent modifications take place that give rise to the mature mRNA, which is transported out of the nucleus for use as the
temple for protein synthesis (translation)
In Eukaryotic organisms primary transcripts are often spliced in multiple combinations of exons, known as
alternative splicing
alternative splicing gives rise to a
family of possible proteins that can have slightly different functions, regulation and/or tissue specificity (i.e. different splice variants are found in different tissues)
what is a gene?
a segment of DNA that is transcribed into RNA and its associated transcriptional control regions
what regulates gene regulation? (2)
promoters and enhancers
what is convolved in gene transcription (2)
RNA polymerase
TF
what is involved in genes and RNA? (7)
axons and introns promoter regions start site and stop site for transcription UTR splicing capping polyadenylation
mRNA (2)
messenger RNA
translated into proteins
tRNA (2)
transfer RNA
transfer amino acids to the growing peptide chain
rRNA (2)
ribosomal RNA
encodes ribosomal proteins
microRNA
Block translation of specific mRNAs and thereby regulate gene expression
siRNA (2)
small interfering RNAs
turn off gene expression by directing the selective degradation of mRNAs.
snoRNA (2)
small nucleolar RNAs
process and chemically modify rRNAs
scaRNA (2)
small cajal RNAs
modify snoRNAs and snRNAs
what are other noncoding RNAs involved in? (3)
telomere synthesis
X-chromosome inactivation
protein transport into the ER
percent abundance of rRNA in a cell
~80%
percent abundance of tRNA in a cell
~15%
percent abundance of mRNA in a cell
~3-5%
percent abundance of other RNA in a cell
<1%
Most protein coding genes are transcribed by
RNA Polymerase II
Transcription initiates at a specific point in the DNA and requires
unwinding of the DNA to create the proper single-stranded template
Gene expression regulatory proteins recognize specific DNA sequences and upon binding regulate
if, when and to what extent a gene is transcribed
Gene expression is regulated by numerous transcription factors that interact with
promoter elements in DNA and/or proteins bound to those promoter elements
The presence/absence of specific factors is an obligatory first step in the initiation of
TBP/TFIID binding and subsequent RNA Polymerase binding
what does TBP TF2D bind to
TATA sequence
what does TF2B bind to?
TF2D/TATA
helices activity
unwind DNA
RNA is not just a — molecule
linear
TF2D subunits (2)
TBP
TAF
TBP subunit
recognizes TATA box
TAF subunit
recognizes other DNA sequences near the transcription start point, regulates DNA binding by TBP
TF2B
recognizes BRE element in promoters; accurately positions RNA polymerase at the start site of transcription
RNA polymerase 1 transcribes (3)
5.8S, 18S, and 28S rRNA genes
RNA polymerase 2 transcribes (5)
all protein coding genes snoRNA genes miRNA genes siRNA genes most snRNA genes
RNA polymerase 3 transcribes (4)
tRNA genes
5S rRNA genes
some snRNA genes
genes for other small RNAs
what does “s” value refer to
their rate of sedimentation in an ultracentrifuge
the larger the S value,
the larger the rRNA
mRNA processing (5)
capping splicing editing polyadenylation transport
RNA splicing is performed by the
spliceosome
spliceosome is largely made up of
snRNAs in complex with 7 protein subunits to form a SNP
snRNAs involved in splicing are (5)
U1, U2, U4, U5 and U6
The snRNAs provide for
proper base pairing with the mRNA
These RNA-RNA arrangements are
dynamic and shift throughout the splicing process
lariat
associated with splicing
Many mRNAs can be spliced in various ways to produce different combinations of exons depending upon the
tissue and/or the types of cell signals present/absent
The human genome contains — genes, but the human proteome is estimated to contain —
~20,000-25,000
~250,000 proteins
most heavily spliced genes
alpha tropomyosin gene
different sliced forms of the alpha tropomyosin gene (5)
striated muscle mRNA smooth muscle mRNA fibroblast mRNA fibroblast mRNA brain mRNA
The 5’cap and splicing of the primary mRNA transcript occur as soon as the
hnRNA emerges from the RNA polymerase
The poly-A tail is added to the 3’end of the mRNA by a set of
RNA-binding proteins and RNA-processing enzymes as soon as it emerges from the RNA polymerase
Mature mRNA is then exported from the nucleus through a specific export receptor mediated process involving (2)
nuclear bound proteins, some of which are shed during export, and cytoplasmic (ER) located initiation factors involved in protein synthesis
miRNA (2)
small non-coding RNA
~21-25 nt in length
how does miRNA regulate translation? (3)
Bind to 3’UTR of target mRNA to form an RNA-inducing silencing complex (RISC)
Suppress protein synthesis and/or induce mRNA degradation
Each miRNA can target multiple (up to 100) different mRNAs
what does pri-mRNA form
a hairpin structure
mature mRNA is a
single string
the mature mRNA can bind to the ..
3’ UTR of target mRNA to interrupt protein synthesis
- bases code for one amino acid
3
3 base sequence is known as a
codon
The genetic code is “—” for all organisms it is essentially the same
universal
“commaless”
read from beginning to end so reading frame is critical
Degenerate:
more than one codon can make the same amino acid
The third base in the triplet codon is less — that the first two
specific
3 of the 64 possible codons do not code for amino acids, but signal —
termination
Roberts syndrome
Prenatal growth retardation (mild to severe), craniofacial abnormalities such as microcephaly and cleft lip/palate and limb malformations (usually limbs are short and the arms are more severely affected than legs).
what mutation occurs with Roberts syndrome?
Homozygous mutation of ESCO2
Homozygous mutation of ESCO2 encodes
an acetyltransferase important for the formation of the cohesion complex that binds to chromosomes and creates cohesion between sister chromatids
Closely related to Cornelia de Lange Syndrome (mutations in Smc1, Smc3, NIPBL), collectively referred to as
Cohesionopathies
Studies suggest that the ESCO2 mutations lead to decreased rDNA transcription and subsequent ribosomal biogenesis and the observed defects in
nucleolar morphology
This leads to decreased
protein synthesis
