YouTube Transcript: DNA transcription and translation McGraw Hill | YouTubeToText
YouTube Transcript: DNA transcription and translation McGraw Hill
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in order for our bodies to function we
need to supply them with a variety of
nutrients we get from our diet
our bodies cannot use the food as it is
when it enters our digestive system the
process of chemical digestion uses
different proteins and enzymes to break
down the food particles into usable
nutrients our cells can absorb
and where are the instructions to
manufacture these and all the different
types of proteins we need to stay alive
the instructions to make proteins are
contained in our DNA DNA contains genes
a gene is a continuous string of
nucleotides containing a region that
codes for an RNA molecule this region
begins with a promoter and ends in a
terminator genes also contain regulatory
sequences that can be found near the
promoter or at a more distant location
for some genes the encoded RNA is used
to synthesize a protein in a process
called gene expression for these genes
expression can be divided into two
processes transcription and translation
in eukaryotic cells transcription occurs
in the nucleus where DNA is used as a
template to make messenger RNA then in
translation which occurs in the
cytoplasm of the cell
the information contained in the
messenger RNA is used to make a
polypeptide
during transcription the DNA in the gene
is used as a template to make a
messenger RNA strand with the help of
the enzyme RNA polymerase this process
occurs in three stages initiation
elongation and termination during
initiation the promoter region of the
gene functions as a recognition site for
RNA polymerase to bind this is where the
majority of gene expression is
controlled by either permitting or
blocking access to this site by the RNA
polymerase binding causes the DNA double
helix to unwind and open then during
elongation the RNA polymerase slides
along the template DNA strand as the
complementary bases pair up the RNA
polymerase links nucleotides to the
three prime end of the growing RNA
molecule
once the RNA polymerase reaches the
terminator portion of the gene the
messenger RNA transcript is complete and
the RNA polymerase the DNA strand and
the messenger RNA transcript dissociate
from each other
the strand of messenger RNA that is made
during transcription includes regions
called
exons that code for a protein and
non-coding sections called introns in
order for the messenger RNA to be used
in translation the non-coding introns
need to be removed and modifications
such as a five prime cap and a 3 prime
poly a tail are added
this process is called introns splicing
and is performed by a complex made up of
proteins and RNA called a spliceosome
this complex removes the intron segments
and joins the adjacent exons to produce
a mature messenger RNA strand that can
leave the nucleus through a nuclear pore
and enter the cytoplasm to begin
translation
how is the information in the mature
messenger RNA strand translated into a
protein the nitrogenous bases are
grouped into three letter codes called
codons
the genetic code includes 64 codons most
codons code for specific amino acids
there are four special codons one that
codes for start and three that code for
stop
translation begins with the messenger
RNA strand binding to the small
ribosomal subunit upstream of the start
codon each amino acid is brought to the
ribosome by a specific transfer RNA
molecule the type of amino acid is
determined by the anticodon sequence of
the transfer RNA
complementary base pairing occurs
between the codon of the messenger RNA
and the anticodon of the transfer RNA
after the initiator transfer RNA
molecule binds to the start codon the
large ribosomal subunit binds to form
the translation complex and initiation
is complete
in the large ribosomal subunit there are
three distinct regions called the e P
and a sites
during elongation individual amino acids
are brought to the messenger RNA strand
by a transfer RNA molecule through
complementary base pairing of the codons
and anticodons each Eddie codon of a
transfer RNA molecule corresponds to a
particular amino acid
a charged transfer RNA molecule binds to
the a site and a peptide bond forms
between its amino acid and the one
attached to the transfer RNA molecule at
the P site
the complex slides down one codon to the
right where the now uncharged transfer
RNA molecule exits from the e site and
the a site is open to accept the next
transfer RNA molecule
elongation will continue until a stop
codon is reached
a release factor binds to the a site at
a stop codon and the polypeptide is
released from the transfer RNA in the P
site the entire complex dissociates and
can reassemble to begin the process
again at initiation the purpose of
translation is to produce polypeptides
quickly and accurately
after dissociation the polypeptide may
need to be modified before it is ready
to function
modifications take place in different
organelles for different proteins
in order for a digestive enzyme to be
secreted into the stomach or intestines
the polypeptide is translated into the
endoplasmic reticulum
modified as it passes through the Golgi
then secreted using a vesicle through
the plasma membrane of the cell into the
lumen of the digestive tract
proteins are needed for most
physiological functions of the body to
occur properly such as breaking down
food particles in digestion and the
processes of transcription and
translation make the production of
proteins possible
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