Protein Synthesis

• Protein synthesis
• Two step process by which an organism’s DNA (genes) are translated into proteins.
• Why do we need proteins?
• Structure, repair, and growth
• Enzymes – control metabolism (sum of all life’s processes)
• Hormones & steroids – control growth and development

Protein Synthesis

• Protein synthesis involves 2 types of nucleic acids: DNA and RNA.

Protein Synthesis

• Protein synthesis involves 2 types of nucleic acids: DNA and RNA.
• RNA = ribonucleic acid (3 types)
• mRNA – messenger RNA takes information for protein to be made from DNA to the ribosome.
• tRNA – transfer RNA carries amino acids to ribosomes, lines them up in the correct order according to mRNA.
• rRNA – ribosomal RNA makes up the structure of the ribosome.
• RNA nucleotides are composed of phosphate, ribose (sugar) and a nitrogen base (adenine, guanine, cytosine and uracil).

Protein Synthesis

• Occurs in 2 steps
• Step 1: Transcription
• Taking DNA and transcribing it into RNA.
• Occurs in the nucleus.
• Step 2: Translation
• Taking RNA and translating it into amino acids (monomers of protein).
• Occurs out in the cytoplasm in ribosomes.

“THE BIG PICTURE”

Transcription

Translation

Protein Synthesis- Transcription

• Changing DNA to mRNA.
• How does it begin?
• An enzyme unzips the DNA double helix (Helicase).
• RNA polymerase binds to the DNA sequence and transcribes an mRNA sequence.
• Which means that it binds free nucleotides to the unzipped DNA molecule according to Chargaff’s rules.

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- Example: DNA: A A C T G A T G C

RNA: U U G A C U A C G

Protein Synthesis- Transcription

• After the mRNA is made, it is released and an enzyme zips (helicase) the DNA back up (by reforming the hydrogen bonds).

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Protein Synthesis- Transcription

• Transcription Practice #1:

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• Transcription Practice #2:

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DNA

mRNA

DNA

mRNA

Protein Synthesis- Transcription

• Okay…we made mRNA, now what?
• mRNA takes the genetic information out of the nucleus into the cytoplasm to a ribosome.

ribosome

cytoplasm

nucleus

• Changing mRNA to proteins (amino acids).

- How does it begin?

• mRNA arrives at the ribosome.
• tRNA brings amino acids to the ribosome to match up to the mRNA according to Chargaff’s rules.
• Every THREE nucleotide bases on the mRNA represents a codon …the tRNA that matches it is the anticodon and brings in the appropriate amino acid.

- Example: DNA: A A C T G A T G C

mRNA: U U G A C U A C G

Amino Acids: LEU- THR- THR

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Protein Synthesis- Translation

Transcription 🡪

Translation 🡪

Protein Synthesis- Translation

• Find the amino acid coded for by:
• AUG
• CAU
• GGG
• UAA
• UAG
• UGA

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🡪 Met (start)

🡪 His

🡪 Gly

🡪 Ter (stop)

🡪 Ter (stop)

🡪 Ter (stop)

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• There are 64 possible codons.
• Only 23 amino acids, therefore some amino acids may be coded by more than one codon.
• There are special START and STOP sequences (codons).
• START codon = AUG 🡪 codes for the amino acid methionine.
• STOP codons = UGA, UAG, UAA
• These STOP codons signal the end of an amino acid chain (protein) being made.
• They are also called termination codons (ter).

Protein Synthesis- Translation

Protein Synthesis- Translation

This animation is showing the t-RNA bringing the correct amino acid to the ribosome (not shown) according to the m-RNA’s “message” ( its codons).

m-RNA

t-RNA