Genes are expressed when-
information inside the DNA affects the cells properties and activity.
What mediates gene expression?
RNA
Transcription is
DNA is synthesized to make RNA
What needs to occur so that an mRNA is produced?
a gene sequence of DNA needs to be identified
mRNA is modified by-
RNA splicing, 5' end capping and the additions of a poly(A) tail after which the mature mRNA enters the cytoplasm
Mature mRNA is where translation occurs, what is another reason why mature mRNA different from Pre-mRNA
Post-transcriptional modifications occur in mature mRNA and are found in the cytoplasm, ribosomes and ER
An exon is a
coding sequence
An intron is a
noncoding sequence
What are the steps that mRNA undergoes before it is translated into a protein?
- 2 ends of RNA are modified
- introns are removed by an enzymatically catalyzed RNA splicing action
-resulting mRNA is transported from the nucleus to the cytoplasm
what are the four distinct types of RNA?
rRNA, tRNA, mRNA, miRNA
What is the function of rRNA?
it translates and synthesizes proteins
What is the function of tRNA?
transfers amino acids to make proteins during translation
What is the function of mRNA
RNA that has left the nucleus, codes for proteins
What is the function of miRNA
regulates gene expression by blocking the translation of specific mRNAs and causing degradation.
about 80% of total RNA in the cell is-
rRNA (associates with proteins to form ribosomes)
types of rRNA molecules
5S, 5.8S, 18S, 28S
The smallest RNA is
tRNA (carries approrpiate amino acids)
About 5% of total RNA is
mRNA (carries genetic information from DNA to cytosol for translation)
miRNA is-
encoded by genes and are single-stranded RNA molecules that are 21 to 23 nucleotides in length
miRNA are ________________ but NOT _________________
transcribed, translated
miRNA functions in regulating gene expression by-
their ability to bind mRNA and to down-regulate the gene expression
A gene is-
the minimal linear sequence of genomic nuclei acids that encodes proteins and structural RNA
Gene sequences are written from-
5' to 3'
Genes in eukaryotic cells are composed of -
coding exons, noncoding introns, and noncoding consensus sequences
What is a consensus sequence?
are recognition markers and are conserved.
introns and exons differ in-
number, size, location, and sequence from gene to gene
noncoding regions at the 5' end to the 1st axon is referred to as-
upstream sequences
Noncoding regions at the 3' end are termed-
downstream sequences
What is a promoter?
DNA sequences that selected or determine the start site of RNA synthesis
What is the TATA box
the consensus sequence for promotes that is often located 15-30 base pairs upstream from the transcription start site
what binds to the TATA box in eukaryotic cells?
proteins known as transcription/basal factors BIND to the TATA box and facilitate binding of RNA polymerase II
Introns always begin with _____ and end with _______
(this sequence is essential for splicing out introns out of the primary transcript)
Guaninne and Uracil; Adenine and Guanine
RNA synthesis occurs-
in the nucleus and is catalyzed by RNA polymerase
RNA is made of the sugar
ribose
What is the function of RNA polymerase I
synthesizes rRNAs involved in facilitating protein synthesis by the ribosome
RNA polymerase II is responsible for-
the synthesis of mRNA and miRNAS
RNA polymerase III-
catalyzes the synthesis of tRNAs
What is the coding region
a region that contains DNA sequence that is transcribed to mRNA, which is then transcribed to a protein
What is the regulatory region?
consists of two classes of sequences
-ensures basal expression
-regulated expression
What are the two components in basal promoter sequences?
proximal and distal component
What is the proximal component
TATA box, directs RNA polymerase II to correct site
What is the distal component?
specifies the frequency of initation (CAAT and GC) boxes
what regulates gene expression?
enhancers and response elements
formation of the transcription complex requires-
several proteins in addition to RNA polymerase II
RNA polymerase is a
dna- dependent RNA polymerase and it uses its formation from DNA to synthesize a complementary sequence
Only ____ strand of the gene is used as a template for __________ and is referred to as the ________
one, transcription, template strand
RNA polymerase reads DNA _____ and produces an RNA molecule complementary to it
3'-5'
mRNA in the nucleus is NOT
functional
mRNA in the cytoplasm is
mature