Transcription AND Translation

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Transcription ANDTranslation

• By Michael and Nick

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Background Information

• The GENOTYPE of an organism is its genetic
  makeup described as the sequence of nucleotide
  bases in the organisms DNA.
• The PHENOTYPE of an organism is its physical
  traits it is the result of many actions
  performed by different proteins.
• Examples of proteins include enzymes of
  structural proteins.

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Background Information

• DNA codes for the building, or synthesis, of
  proteins.
• Genes send the instructions for building proteins
  in the form of RNA.
• RNA then codes for the synthesis of proteins.
• Central Dogma is the term that describes this
  process. Term coined by Francis Crick.

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Background Information

• DNA is located in the nucleus of the cell.
• TRANSCRIPTION occurs and DNA information is
  transferred to RNA.
• TRANSLATION occurs and protein synthesis takes
  place in the cytoplasm of the cell.

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Background Information

• DEFINITIONS
• TRANSCRIPTION is defined as the transfer of
  genetic information from DNA into an RNA
  molecule. (page 178)
• TRANSLATION is defined as the transfer of the
  information from RNA into a protein. (page 178)

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Overview

• DNA and RNA are both polymers.
• The monomers of DNA and RNA are linked together
  in certain sequences that are used to convey
  information.
• DNA has the nitrogenous bases labeled A, T, C,
  and G (on their nucleotides).
• RNA has the nitrogenous bases labeled A, U, C,
  and G (on their nucleotides).

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Overview

• The double helix of DNA consists of linear
  sequences of nucleotide bases.
• The genes on a strand of DNA are made up of the
  specific sequences of these bases.

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Overview

• The genetic information that is used to build the
  amino acid sequence of a polypeptide chain is
  written in DNA and RNA it is written in the form
  of codons.

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Overview

• A codon is a three-nucleotide sequence located in
  DNA that is transcribed into a three-base codon
  in RNA the codons are complementary.
• The RNA codon is then translated into the amino
  acid sequence. Amino acid sequences eventually
  form a polypeptide.

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Overview

• Summary one codon consists of three nucleotides.
• One DNA codon
• One RNA codon
• One amino acid

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TRANSCRIPTION
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• The transfer of genetic information from DNA to
  RNA.

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• The first step of transcription involves two DNA
  strands separating at the location where the
  process will take place.
• One strand of this DNA serves as the template for
  building the new molecule of RNA.

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• The new RNA molecule consists of nucleotides that
  take their places along the DNA strand (using the
  DNA strand as a template).
• The nucleotides of RNA form hydrogen bonds with
  the nucleotide bases that are on the strand of
  DNA.
• RNA nucleotides are then linked by RNA
  polymerase, the transcription enzyme.

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• RNA polymerase is defined as an enzyme that links
  together the growing chain of RNA nucleotides
  during transcription, using a DNA strand as a
  template.
• The base-pairing rules that apply to DNA also
  apply to RNA, except that RNA has the base U
  rather than T.

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• DNA nucleotides form specific sequences that tell
  the RNA polymerase where it should start and stop
  the process of transcribing information.
• There are three main steps that describe this
  process

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Step One Initiation of Transcription

• A promoter, which is located in the DNA, is a
  nucleotide sequence that signals RNA polymerase
  to begin transcribing (located at the start of
  the gene).
• Initiation of Transcription the attachment of
  RNA polymerase to the promoter and the start of
  RNA synthesis. (page 181)
• The promoter also determines which of the two
  strands of DNA is to be transcribed on a gene.

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Step Two RNA Elongation

• Elongation is the stage in which RNA grows
  longer.
• As the RNA continues to be synthesized, it begins
  to peel off of the DNA strand.
• The two DNA strands then come back together,
  forming the double helix that the DNA originally
  started with.

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Step Three Termination of Transcription

• The terminator, or the special sequence of bases
  located in the DNA template, is reached by RNA
  polymerase.
• The terminator signals the end of the gene.
• RNA polymerase then unhooks itself from the
  molecule of RNA as well as the gene.
• Transcription therefore produces the RNA that
  codes for the sequence of amino acids.

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Processing Eukaryotic RNA

• Eukaryotic cells perform transcription in the
  nucleus, but they also process the RNA
  transcripts in the nucleus before they go to the
  cytoplasm (where translation by the ribosomes
  takes place).
• One type of RNA processing adds a cap and tail
  (nucleotides) to the ends of the RNA. This gives
  protection from cellular enzymes and also helps
  the ribosomes to recognize the RNA as being the
  messenger RNA (mRNA).

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Processing Eukaryotic RNA

• Genes include both introns (internal noncoding
  regions) and exons (coding regions the parts of
  a gene that are expressed). Both are transcribed
  from the DNA to the RNA.
• Before RNA leaves the nucleus, the introns are
  removed and the exons join together to form one
  strand a continuous coding sequence, which
  makes up the mRNA molecule. (page 182)
• This process is known as RNA splicing. The mRNA
  is now ready for translation.

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TRANSLATION
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• The synthesis of a polypeptide using the genetic
  information encoded in an mRNA molecule.

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• The tools and processes that are used to
  translate mRNA need both enzymes and sources of
  chemical energy, including ATP.
• Translation also requires transfer RNA (tRNA) and
  ribosomes.

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Transfer RNA

• The translation of genetic messages from mRNA
  into the amino acid language used by proteins
  relies on an interpreter transfer RNA.
• tRNA converts the codons of nucleic acids into
  the amino acid languange that is used to form
  proteins.

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Transfer RNA

• Cells that make proteins contain many amino acids
  in their cytoplasm.
• The job of the tRNA molecules is to match the
  amino acids with the correct codons, in order to
  make the new polypeptide.

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Transfer RNA

• tRNA molecules must perform two functions to
  carry out this task
• Pick up the appropriate amino acids.
• Recognize the appropriate codons in the mRNA.
• (page 183)

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Transfer RNA

• tRNA molecules are made of single strands of RNA
  that twist and fold in many different places,
  forming double-stranded regions.
• The ends of the folded molecules are known as
  anticodons because they are a special triplet of
  bases. (page 183)
• Anticodons are defined as specific sequences of
  three nucleotides that are complementary to a
  codon triplet on mRNA. (page G-2)

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Ribosomes

• Ribosomes, along with making the polypeptides,
  help the mRNA and the tRNA to function properly.
• Ribosomes are made of two different subunits
  protein and ribosomal RNA (rRNA)
• Fully assembled ribosomes have binding spots for
  mRNA on their small subunit and binding spots for
  tRNA on their large subunit. (page 183)

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Ribosomes

• tRNA has two binding sites
• The P site, which holds the tRNA that carries the
  polypeptide chain as it grows.
• The A site, which holds the tRNA that carries the
  next amino acid that is going to be connected to
  the chain.
• Anticodons of tRNA then pair with the codons of
  mRNA, and they are held together by the two
  different subunits of the ribosome.
  (page 183)

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Ribosomes

• Finally, the ribosome is able to join the amino
  acid from the A site of the tRNA to the
  polypeptide chain, which is now growing. (page
  183)

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The Process of Translation

• Translation is also divided into three stages.
  The three stages are initiation, elongation, and
  termination.

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Stage One Initiation

• Initiation brings the mRNA, the first amino acid
  (including its tRNA that is attached), and the
  two subunits of a ribosome together. (page 184)
• This process determines the specific location
  where translation will begin, so that the mRNA
  codons get translated in the proper sequence of
  amino acids. (page 184)

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Stage One Initiation

• This process occurs in two steps
• mRNA connects to the small ribosomal subunit and
  tRNA connects to the start codon.
• The large ribosomal subunit joins with the small
  ribosomal subunit, and a working ribosome is
  established. The initiator tRNA also fits into
  the P site that is located on this ribosome.
• (page 184)

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Stage Two Elongation

• Elongation is a three-step process
• Codon recognition takes place the process in
  which tRNAs anticodon joins with mRNAs codon in
  the A site, bringing an amino acid with it.
• Peptide bond formation takes place the
  polypeptide connects to the amino acid in the A
  site of the tRNA molecule and the ribosome acts
  as a catalyst for the formation of the bond.
• Translocation takes place the ribosome now moves
  the tRNA (that remains) to the P site, and it
  brings the growing polypeptide with it as well
  the tRNA and mRNA move together the next mRNA
  codon is brought into the A site and the process
  begins anew.
• (page 184)

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Stage Three Termination

• The stop codons in mRNA eventually reach the A
  site of ribosomes, telling the process of
  translation to stop.
• The finished polypeptide is released and the
  ribosome then splits back into its subunits.
• (page 184)

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Review
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• The flow of genetic information in a cell
• DNA
• RNA
• PROTEIN

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Transcription DNA to RNA

• Takes place in the nucleus.
• Processes RNA before it is able to enter into the
  cytoplasm.

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Translation RNA to Protein

• Takes place in the cytoplasm.
• While polypeptides are being made, they fold and
  coil. This is responsible for the tertiary
  structure of proteins.
• Quaternary structure occurs when many
  polypeptides join together.

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Overall

• Information in a Gene, or the certain sequence of
  nucleotides in DNA
• Gene causes the transcription of a complementary
  sequence of nucleotides in mRNA
• mRNA determines the sequence of the amino acids
  in the polypeptide
• Polypeptides form specific proteins
• The capabilities and the appearance of cells and
  organisms is established

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Why is this important?
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• Transcription and translation are the ways in
  which the genotype produces the phenotype. (page
  185)
• In other words, these processes allow genes to
  control both the structures and the activities of
  our cells. (page 185)

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The End