rna & protein synthesis
DESCRIPTION
RNA & Protein Synthesis. Ribose. RNA. Hydrogen bonds. Mrs. Stewart Biology I. Uracil. Adenine. Genes. A gene is a section of the DNA sequence that codes for a protein. Each unique gene has a unique sequence of bases. - PowerPoint PPT PresentationTRANSCRIPT
RNA & Protein Synthesis
Uracil
Hydrogen bonds
Adenine
RiboseRNA
Mrs. StewartBiology I
Genes
A gene is a section of the DNA sequence that codes for a protein.
Each unique gene has a unique sequence of bases.
This unique sequence of bases will code for the production of a unique protein.
It is these proteins and combination of proteins that determine the phenotypes for our traits.
DNA
Trait
How do we get from here, to there?
DNA
Trait
Protein
RNA
GENE
REVIEW: Structure of RNA
All forms of RNA have: Single stranded chain
of nucleotides RNA nucleotides
composed of:
1. Phosphate
2. Ribose sugar
3. Nitrogenous base
4 Nitrogen bases of RNA:
1. Guanine
2. Cytosine
3. Adenine
4.Uracil
DNA RNA
Structure Double Stranded
Single Stranded
Bases- Purines Adenine (A)
Guanine (G)
Adenine (A)
Guanine (G)
Bases - Pyrimidines
Cytosine (C)
Thymine (T)
Cytosine (C)
Uracil (U)
Sugar Deoxyribose Ribose
Differences between DNA and RNA:
RNA’s JOB= Make Proteins!!
Types of RNA
1) messenger RNA (mRNA)- carries instructions (the message) from the DNA in the nucleus to the ribosome
Types of RNA
2) ribosomal RNA (rRNA)- combines with proteins to form the ribosome (proteins made here)
3) transfer RNA (tRNA)- transfers each amino acid to the ribosome as it is specified by coded messages in mRNA during the construction of a protein
Protein Synthesis Overview
There are two steps to making proteins (protein synthesis):
1) Transcription (occurs in the nucleus)DNA RNA
2) Translation (occurs in the cytoplasm)RNA protein
Transcription occurs in three main
steps:
Initiation:
Transcription begins when the enzyme RNA polymerase binds to the DNA at a promoter site.
Promoters are signals in the DNA strand (a certain sequence of bases) that indicate to the enzyme where to bind to make RNA.
Elongation: The enzyme separates
the DNA strands by breaking the hydrogen bonds, and then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA.
RNA polymerase pairs up free floating RNA nucleotides with DNA template and joins the nucleotides together to form the backbone of the new mRNA strand.
Termination When mRNA hits a termination sequence, it separates
from the DNA
Transcription vs. Replication
The main difference: Transcription results in one single-stranded mRNA molecule. Replication results in two double-stranded DNA molecules.
Practice
DNA template
DNA Complement (replication)
mRNA (transcription)
ATTCGGAGC
TAAGCCTCG
UAAGCCUCG
mRNA synthesis animation
transcription animation
What is the purpose of the genetic code in DNA?
Transcription
RNADNA
RNApolymerase
Adenine (DNA and RNA)Cytosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)
Nucleus
After we transcribe the message so it can leave the nucleus, we then must have
a way to “read” the message.
The Genetic Code The “language” of mRNA instructions is
called the genetic code.
This code is written in a language that has only four “letters” (A,G,C,U)
How can a code with just 4 letters carry instructions for 20 different amino acids?
The Genetic Code – what does it code for?
Proteins (polypeptides) - long chains of amino acids that are joined together.
There are 20 different amino acids. The structure and function of
proteins are determined by the order (sequence) of the amino acids
The Genetic Code
A codon consists of three consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide (protein).
The four bases (letters) of mRNA (A, U, G, and C) are read three letters at a time (and translated) to determine the order in which amino acids are added to a protein.
The genetic code is read 3 letters at a time.
The Codon Wheel
64 different mRNA codons are possible in the genetic code.
More than one codon can code for the same amino acid Example: GGG,
GGU, GGA, GGC = Glycine
Some codons give instructions Example: AUG =
start Example: UGA,
UAA, UAG = Stop
Cracking the Secret Code
To decode a codon:
start at the middle of the circle and move outward.
Ex: CGA = Arginine
Ex: GAU = Aspartic Acid
Cracking the Code This picture shows the amino
acid to which each of the 64 possible codons corresponds.
To decode a codon, start at the middle of the circle and move outward.
Ex: CGA
Arginine
Ex: GAU
Aspartic Acid
Translation Translation takes place on
ribosomes, in the cytoplasm or attached to the ER.
rRNA and tRNA will decode the message on the mRNA strand to produce a polypeptide chain (protein).
http://www.youtube.com/watch?v=5bLEDd-PSTQ
Messenger RNA (mRNA)
The mRNA that was transcribed from DNA during transcription, leaves the cell’s nucleus and enters the cytoplasm.
Transfer RNA (tRNA)
Transfer RNA (tRNA) molecules in the cytoplasm will bond with a specific amino acid
Then, tRNA carries that amino acid to the ribosome
Each tRNA molecule has three unpaired bases called an anticodon.
These bases are complementary to one codon on the mRNA strand.
tRNA molecule
Anticodon
Translation
Initiation Begins when an
mRNA in the cytoplasm attaches to the ribosome.
AUG = the start codon
AUG = methionine
The Polypeptide “Assembly Line”tRNA anticodon will
temporarily bind to the complementary codon on the mRNA molecule in the ribosome.
(This binding of codon to anticodon ensures the correct amino acid is being added)
Elongation The ribosome has two binding sites, allowing two tRNA molecules to line
up, side by side
The ribosome forms a peptide bond between the first and second amino acids on those tRNA molecules
At the same time, the ribosome breaks the bond that held the first tRNA molecule to its amino acid and releases the tRNA molecule.
The Polypeptide “Assembly Line”The tRNA floats away, allowing the ribosome to move down the mRNA molecule and bind another tRNA.
The ribosome continues to move along the mRNA, attaching new tRNA molecules and adding more amino acids to the polypeptide chain.
Termination
The process continues until the ribosome reaches one of the three stop codons on the mRNA.
Then, the ribosome detaches from the mRNA.
The result is a polypeptide (protein chain) that is ready for use in the cell.
Practice DNA template
mRNA (transcription)
tRNA
Amino Acid Sequence (translation)
TAC GGT CCA AAC ACT
AUG/CCA/GGU/UUG/UGA
UAC/GGU/CCA/AAC/ACU
Met-Pro-Gly-Leu-Stop
Computer Practice for transcription and translation
http://learn.genetics.utah.edu/content/begin/dna/transcribe/
http://www.youtube.com/watch?v=Ikq9AcBcohA
All organisms use the same genetic code (A,T,C,G).
This provides evidence that all life on Earth evolved from a common origin.