Download Transcription AND Translation

Transcription
AND
Translation
By Michael and Nick
Background Information
• The GENOTYPE of an organism is its
genetic makeup; described as the
sequence of nucleotide bases in the
organism’s 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.
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.
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.
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)
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).
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.
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.
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.
Overview
• Summary: one codon consists of three
nucleotides.
One DNA codon
One RNA codon
One amino acid
The transfer of
genetic
information from
DNA to RNA.
• 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.
• 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.
• 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.
• 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:
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.
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.
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.
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).
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.
The synthesis of a
polypeptide using the
genetic information
encoded in an mRNA
molecule.
• 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.
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.
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.
Transfer RNA
•
tRNA molecules must perform two
functions to carry out this task:
1. Pick up the appropriate amino acids.
2. Recognize the appropriate codons in the
mRNA.
(page 183)
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)
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)
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)
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)
The Process of Translation
Translation is also divided into
three stages. The three stages
are initiation, elongation, and
termination.
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)
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)
Stage Two: Elongation
• Elongation is a three-step process:
– Codon recognition takes place: the process in which
tRNA’s anticodon joins with mRNA’s 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)
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)
The flow of genetic information in a cell:
DNA
RNA
PROTEIN
Transcription: DNA to RNA
• Takes place in the nucleus.
• Processes RNA before it is able to enter
into the cytoplasm.
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.
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
• 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)