Protein Synthesis:

Creating proteins from DNA

Review

• DNA is located in the nucleus of eukaryotic cells. Found in the cytoplasm of prokaryotes

» DNA Replication the process of synthesizing a new strand of DNA; Semi conservative

What are the steps in DNA Replication?

DNA vs. RNA DNA is a blueprint to make RNA or Ribonucleic Acid.

DNA Double Stranded In the nucleus only Adenine - Thymine Cytosine - Guanine Deoxyribose sugar

RNA Single stranded In cytoplasm and

nucleus Adenine – Uracil

(thymine is replaced by uracil)

Cytosine – Guanine Ribose sugar

Types of RNA (Ribonucleic acid)

rRNA – ribosomal RNA, the principle component of ribosomes. Site where amino acids are joined together to form Proteins

mRNA – Messenger RNA, carries the DNA code from the nucleus to the ribosome.

tRNA – Transfer RNA, carries amino acids to ribosome

DNA cannot leave nucleus, therefore genetic information must be copied into RNA

The copies (RNA) are then sent into the cytoplasm to make proteins. These copies are single strands of RNA.

Transcription occurs 5’ to 3’ direction

Step 1:Transcription (DNA to RNA)

RNADNA

RNApolymerase

Figure 12–14 TranscriptionSection 12-3

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

Steps in Transcription

1. Helicase: unwinds DNA helix2. RNA Polymerase: finds and matches free floating RNA

nucleotides to DNA.These free nucleotides once put in order forms the RNA.

When it reaches the stop sequence, polymerase detaches and RNA is free.

3. Ligase: seals the DNA Helix4. The RNA strand, now called mRNA, leaves the DNA

molecule and the nucleus.5. Gyrase winds up the DNA strand.

Transcribing rules

DNA to mRNA

A to U

T to A

C to G

G to C

Lets Practice

DNA AAT CCG GCG TAT

mRNA UUA GGC CGC ATA

This molecule of mRNA then passes out of the nucleus and into

the cytoplasm for the second stage

Translation: RNA helps form proteins.

The genetic code (Translation)

Every three nucleotides in mRNA specify a particular amino acid.– This nucleotide triplet is called a codon.

Codons determine amino acids; a chain or amino acids determine that type of protein being made.

The genetic code is the correspondence between nucleotide triplets in DNA and the amino acids

and proteins.

There are 64 possible codons but only twenty different amino acids. More than one codon may specify an amino acid.

“STOP” codons specify the end of an amino acid chain.

Circular Codon Charts

Rectangular Codon Chart

Translation continued

During translation mRNA works with two other types of RNA to build proteins by joining amino acids.

Translation occurs on ribosomes that contain ribosomal RNA or rRNA.

An mRNA molecule passes between the two subunits of a ribosome.

Transfer RNA or tRNA , carries amino acids to the ribosome.

The tRNA has an anticodon, which is a three nucleotide sequence, which are complementary to mRNA codons.

Amino acids are added to the growing protein chain until the stop codon is reached.

Figure 12–18 TranslationSection 12-3

Figure 12–18 Translation (continued)Section 12-3

Translating rules

mRNA to tRNA

U to AA to UC to GG to C

Lets Practice

DNA AAT CCG GCG TAT

mRNA UUA GGC CGC AUA

tRNA AAU CCG GCG UAU