0:00 in order for our bodies to function we
0:02 need to supply them with a variety of
0:04 nutrients we get from our diet
0:07 our bodies cannot use the food as it is
0:10 when it enters our digestive system the
0:13 process of chemical digestion uses
0:15 different proteins and enzymes to break
0:18 down the food particles into usable
0:20 nutrients our cells can absorb
0:23 and where are the instructions to
0:25 manufacture these and all the different
0:27 types of proteins we need to stay alive
0:30 the instructions to make proteins are
0:32 contained in our DNA DNA contains genes
0:37 a gene is a continuous string of
0:39 nucleotides containing a region that
0:42 codes for an RNA molecule this region
0:45 begins with a promoter and ends in a
0:48 terminator genes also contain regulatory
0:51 sequences that can be found near the
0:54 promoter or at a more distant location
0:56 for some genes the encoded RNA is used
1:00 to synthesize a protein in a process
1:02 called gene expression for these genes
1:06 expression can be divided into two
1:08 processes transcription and translation
1:12 in eukaryotic cells transcription occurs
1:16 in the nucleus where DNA is used as a
1:19 template to make messenger RNA then in
1:23 translation which occurs in the
1:25 cytoplasm of the cell
1:26 the information contained in the
1:28 messenger RNA is used to make a
1:31 polypeptide
1:33 during transcription the DNA in the gene
1:36 is used as a template to make a
1:38 messenger RNA strand with the help of
1:40 the enzyme RNA polymerase this process
1:44 occurs in three stages initiation
1:47 elongation and termination during
1:52 initiation the promoter region of the
1:54 gene functions as a recognition site for
1:56 RNA polymerase to bind this is where the
2:00 majority of gene expression is
2:02 controlled by either permitting or
2:04 blocking access to this site by the RNA
2:07 polymerase binding causes the DNA double
2:10 helix to unwind and open then during
2:14 elongation the RNA polymerase slides
2:17 along the template DNA strand as the
2:21 complementary bases pair up the RNA
2:23 polymerase links nucleotides to the
2:26 three prime end of the growing RNA
2:28 molecule
2:31 once the RNA polymerase reaches the
2:34 terminator portion of the gene the
2:36 messenger RNA transcript is complete and
2:39 the RNA polymerase the DNA strand and
2:42 the messenger RNA transcript dissociate
2:45 from each other
2:48 the strand of messenger RNA that is made
2:51 during transcription includes regions
2:54 called
2:54 exons that code for a protein and
2:57 non-coding sections called introns in
3:00 order for the messenger RNA to be used
3:03 in translation the non-coding introns
3:06 need to be removed and modifications
3:09 such as a five prime cap and a 3 prime
3:12 poly a tail are added
3:14 this process is called introns splicing
3:18 and is performed by a complex made up of
3:20 proteins and RNA called a spliceosome
3:25 this complex removes the intron segments
3:28 and joins the adjacent exons to produce
3:30 a mature messenger RNA strand that can
3:34 leave the nucleus through a nuclear pore
3:36 and enter the cytoplasm to begin
3:38 translation
3:41 how is the information in the mature
3:44 messenger RNA strand translated into a
3:46 protein the nitrogenous bases are
3:49 grouped into three letter codes called
3:51 codons
3:54 the genetic code includes 64 codons most
3:58 codons code for specific amino acids
4:02 there are four special codons one that
4:05 codes for start and three that code for
4:08 stop
4:10 translation begins with the messenger
4:12 RNA strand binding to the small
4:14 ribosomal subunit upstream of the start
4:17 codon each amino acid is brought to the
4:21 ribosome by a specific transfer RNA
4:24 molecule the type of amino acid is
4:27 determined by the anticodon sequence of
4:29 the transfer RNA
4:32 complementary base pairing occurs
4:35 between the codon of the messenger RNA
4:37 and the anticodon of the transfer RNA
4:42 after the initiator transfer RNA
4:45 molecule binds to the start codon the
4:48 large ribosomal subunit binds to form
4:50 the translation complex and initiation
4:53 is complete
4:56 in the large ribosomal subunit there are
4:59 three distinct regions called the e P
5:02 and a sites
5:05 during elongation individual amino acids
5:09 are brought to the messenger RNA strand
5:11 by a transfer RNA molecule through
5:14 complementary base pairing of the codons
5:16 and anticodons each Eddie codon of a
5:20 transfer RNA molecule corresponds to a
5:23 particular amino acid
5:27 a charged transfer RNA molecule binds to
5:30 the a site and a peptide bond forms
5:33 between its amino acid and the one
5:35 attached to the transfer RNA molecule at
5:37 the P site
5:40 the complex slides down one codon to the
5:43 right where the now uncharged transfer
5:46 RNA molecule exits from the e site and
5:49 the a site is open to accept the next
5:51 transfer RNA molecule
5:55 elongation will continue until a stop
5:58 codon is reached
6:03 a release factor binds to the a site at
6:06 a stop codon and the polypeptide is
6:08 released from the transfer RNA in the P
6:11 site the entire complex dissociates and
6:15 can reassemble to begin the process
6:17 again at initiation the purpose of
6:21 translation is to produce polypeptides
6:23 quickly and accurately
6:26 after dissociation the polypeptide may
6:29 need to be modified before it is ready
6:31 to function
6:33 modifications take place in different
6:35 organelles for different proteins
6:38 in order for a digestive enzyme to be
6:41 secreted into the stomach or intestines
6:43 the polypeptide is translated into the
6:46 endoplasmic reticulum
6:49 modified as it passes through the Golgi
6:52 then secreted using a vesicle through
6:55 the plasma membrane of the cell into the
6:57 lumen of the digestive tract
7:01 proteins are needed for most
7:03 physiological functions of the body to
7:05 occur properly such as breaking down
7:08 food particles in digestion and the
7:10 processes of transcription and
7:12 translation make the production of
7:14 proteins possible
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