In prokaryotes,
mRNA synthesis
is initiated at a promoter sequence on the DNA template comprising two consensus sequences that recruit RNA polymerase. The prokaryotic polymerase consists of a core enzyme of four protein subunits and a σ protein that assists only with initiation.
What is the first step in eukaryotic DNA?
Initiation of eukaryotic
DNA replication
is the first stage of DNA synthesis where the DNA double helix is unwound and an initial priming event by DNA polymerase α occurs on the leading strand. The priming event on the lagging strand establishes a replication fork.
What marks the beginning of a new gene on DNA in eukaryotes?
Primer synthesis
marks the beginning of the actual synthesis of the new DNA molecule. Primers are short stretches of nucleotides (about 10 to 12 bases in length) synthesized by an RNA polymerase enzyme called primase.
When a promoter binds to DNA what happens to the double helix?
The polymerase unwinds the DNA at the position at which transcription (more…) After the RNA polymerase binds tightly to the promoter DNA in this way, it opens up the double helix to
expose a short stretch of nucleotides on each strand
(Step 2 in Figure 6-10).
How does RNA polymerase know where to start transcribing a gene?
To begin transcribing a gene,
RNA polymerase binds to the DNA of the gene at a region called the promoter
. Basically, the promoter tells the polymerase where to “sit down” on the DNA and begin transcribing. … The DNA opens up in the promoter region so that RNA polymerase can begin transcription.
What are the 6 steps of transcription?
RNA then undergoes translation to make proteins. The major steps of transcription are
initiation, promoter clearance, elongation, and termination
.
What are the steps of transcription in prokaryotes?
- Initiation: closed complex formation. Open complex fromation. Tertiary complex formation.
- Elongation.
- Termination:
What is the first step in DNA replication?
Replication occurs in three major steps: the
opening of the double helix
and separation of the DNA strands, the priming of the template strand, and the assembly of the new DNA segment. During separation, the two strands of the DNA double helix uncoil at a specific location called the origin.
Where does DNA replication begin?
Beginning at
the oriC locus
the DNA molecule is pulled apart and two DNA polymerases, one on each strand begin copying on each strand. As they progress the DNA separates more. The boundrary of the separation between single-stranded and double-stranded DNA is called the replication fork.
Where is DNA in eukaryotes?
The nucleus
is particularly important among eukaryotic organelles because it is the location of a cell’s DNA. Two other critical organelles are mitochondria and chloroplasts, which play important roles in energy conversion and are thought to have their evolutionary origins as simple single-celled organisms.
What are the four base pairs in DNA?
There are four nucleotides, or bases, in DNA:
adenine (A), cytosine (C), guanine (G), and thymine (T)
. These bases form specific pairs (A with T, and G with C).
Is the coding strand always 5 to 3?
By convention, the coding strand is the strand used when displaying a DNA sequence. It is presented in the
5′ to 3′ direction
.
What length of DNA is bound by the transcriptional proteins?
As noted in the previous section, transcription factors are proteins that bind to specific DNA sequences in order to regulate the expression of a gene. The binding sequence for a transcription factor in DNA is usually
about 10 or 11 nucleotides long
.
What are the three important events in the process of transcription?
Transcription takes place in three steps:
initiation, elongation, and termination
.
How does RNA polymerase know where the promoter is?
RNA polymerases (or associated general transcription factors) are hypothesized to reach
promoter sequences by facilitated diffusion (FD)
. In FD, a protein first binds to nontarget DNA and then reaches the target by a 1D sliding search.
What is the name of the enzyme that forms at the start of transcription?
The process of transcription begins when an enzyme called
RNA polymerase (RNA pol)
attaches to the template DNA strand and begins to catalyze production of complementary RNA.
