DNA and Protein DNA and Protein SynthesisSynthesis

DNA Does 2 Important Things in a DNA Does 2 Important Things in a Cell:Cell:

1)DNA is capable of replicating itself. Every time a cell divides, each DNA strand makes an exact copy of itself.

2)DNA directs the production of proteins in the cell. DNA contains the instructions on how to make proteins.

The Importance of ProteinsThe Importance of Proteins

Proteins are the workhorses of the cell. They build all of the important structures and carry on most of the important cellular functions.

What types of proteins are made determine everything about the organism and how it functions.

Review of Protein StructureReview of Protein Structure

Proteins are large polymers made of long chains of amino acids.

Amino Acids bind together with peptide bonds.

A protein’s final shape determines its function. This shape is determined by its amino acid sequence.

Protein StructureProtein Structure

Proteins are made by ribosomes.

Amino acids are put together in a long chain which then folds and bends to determine the final shape.

Remember: Shape equals function!

So, it is VERY important that the amino acid sequence is correct!

What determines the correct What determines the correct amino acid sequence in a protein?amino acid sequence in a protein?

The DNA in a cell determines the sequence of amino acids in a protein.

The DNA sequence is a code that determines which amino acid is first, which is second, etc.

DNA determines protein:

DNA leads from afar…..DNA leads from afar…..

The DNA in a cell’s nucleus determines the sequence of amino acids that are put together at the ribosome.

Yet, the DNA never leaves the nucleus!

How does the DNA do this?

Chromosomes to GenesChromosomes to Genes

Messenger RNA (mRNA)Messenger RNA (mRNA)

DNA is able to “tell” the ribosome how to build the protein by sending a messenger….

This comes in the form of an RNA molecule.

Therefore, this is called messenger RNA, or mRNA.

From DNA to ProteinFrom DNA to Protein

Protein Synthesis has 2 main processes:

1) Transcription (“to write”) –making a mRNA molecule

2) Translation – (“to read”) making the protein, using the mRNA as a guide.

Together, these are called Gene Expression

RNA: A Major PlayerRNA: A Major Player

Three types of RNA are used in protein building

mRNA=messenger RNA (made in nucleus—carries the genetic code)

tRNA=transfer RNA (brings amino acids to the ribosome)

rRNA=ribosomal RNA (what ribosomes are made of) Ribonucleic Acid

RNA Vs. DNARNA Vs. DNA

RNA differs from DNA in 3 ways:

RNA is single-stranded; DNA is double-stranded

RNA has Ribose; DNA has Deoxyribose

RNA has Uracil; DNA has Thymine

Uracil is found in RNA only

RNA Vs. DNA

Transcription: Reading the GeneTranscription: Reading the Gene

During transcription, the information in a particular segment of DNA (a gene) is copied into mRNA

Step 1:RNA polymerase binds to a specific

sequence of bases on the DNA called the Promoter. This is the start code.

Transcription: Reading the GeneTranscription: Reading the Gene

Step 2: Helicases unwind the DNA strand in front of the promoter region.

Step 3: RNA polymerase adds and links complementary RNA bases on one side of the DNA, following base pairing rules. (Exception: Adenine in DNA bonds to Uracil)

TranscriptionTranscription

The RNA polymerase eventually reaches a “stop” location in the DNA.

This stop signal is a sequence of bases that marks the end of each gene.

The result is a single strand of RNA

The Genetic CodeThe Genetic Code

To make a correct protein, the amino acids must be put in the proper sequence.

Each segment of 3 nucleotides in DNA codes for 1 amino acid.

Each triplet of DNA bases makes a triplet of mRNA bases—called a Codon.

Codons of mRNACodons of mRNAWhat amino acid comes from the code AUC? GGG? CGA?

Translation: RNA to ProteinsTranslation: RNA to Proteins

Translation is the process of converting the “language” of RNA into the “language” of proteins (amino acid sequences.)

Translation involves mRNA, tRNA, and rRNA.

tRNA: Transfer RNAtRNA: Transfer RNA

Each tRNA is folded into a compact shape.

There are 2 important places on each tRNA:

Terminal end—has 3 bases which match up to mRNA. This is the Anticodon.

Amino Acid attachment site

Translation, Step 1: Start CodonTranslation, Step 1: Start Codon

After leaving the nucleus, the mRNA joins with a ribosome and tRNA.

The mRNA start codon, AUG, signals the beginning of a protein.

The tRNA carrying Methionine binds to the start codon.

Translation Step 2:A new tRNA Translation Step 2:A new tRNA arrives.arrives.

A new tRNA arrives and binds to the next codon on the mRNA.

A peptide bond forms between the first amino acid and the second amino acid.

The first tRNA detaches and leaves its amino acid behind.

The Ribosome Moves down the The Ribosome Moves down the mRNAmRNA

The ribosome moves one codon down the mRNA strand.

Because the anticodon (on the tRNA) is attached to the codon, they move together as a unit.

The amino acid chain grows as each new one binds.

Translation, Step 3: Releasing the Translation, Step 3: Releasing the proteinprotein

The process ends when a stop codon is reached.

The amino acid chain is released, the ribosome complex and mRNA strand fall apart.

Protein Synthesis AnimationsProtein Synthesis Animations

http://bioweb.uwlax.edu/genweb/molecular/theory/translation/trans1.swf

http://www.youtube.com/watch?v=983lhh20rGY&feature=related

http://www.youtube.com/watch?NR=1&feature=endscreen&v=Ikq9AcBcohA