Protein Synthesis

Protein Synthesis

Middle School

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Learning Objectives

• Compare the structure and function of both DNA and RNA molecules.

• Describe transcription, the process of making an mRNA copy from a DNA template.

• Describe translation, the process of using an mRNA message to build a protein.

• Explain the Central Dogma, how information flows from DNA to RNA to protein.

Key Vocabulary

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Transcription

The process of copying a gene's DNA sequence into a messenger RNA (mRNA) in the nucleus.

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Translation

A ribosome reads an mRNA molecule to synthesize a protein by linking specific amino acids together.

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Codon

A sequence of three nucleotides on an mRNA molecule that codes for a specific amino acid.

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Messenger RNA (mRNA)

This RNA carries genetic instructions from the DNA in the nucleus to the ribosome in the cytoplasm.

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Transfer RNA (tRNA)

This RNA carries specific amino acids to the ribosome to be added to the growing protein chain.

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DNA vs. RNA: The Blueprints of Life

Deoxyribonucleic Acid

• Holds the original genetic blueprint for building and maintaining an organism.

• It is a large, double-stranded molecule shaped like a double helix.

• Contains the sugar deoxyribose and the bases Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

• This stable molecule is primarily found inside the cell's nucleus.

Ribonucleic Acid

• Acts as a messenger, carrying out the instructions from the DNA blueprint.

• It is a smaller, single-stranded molecule that is versatile in its function.

• Contains the sugar ribose and uses Uracil (U) in place of Thymine (T).

• This less stable molecule can travel from the nucleus into the cytoplasm.

Multiple Choice

Which of the following is a key difference between DNA and RNA?

• DNA is single-stranded, while RNA is double-stranded.

• DNA contains the sugar ribose, while RNA contains deoxyribose.

• DNA uses the base Uracil (U), while RNA uses the base Thymine (T).

• DNA is found in the nucleus, while RNA can travel into the cytoplasm.

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The Central Dogma & Types of RNA

• The Central Dogma describes genetic information flowing from DNA to RNA to protein.

• Messenger RNA (mRNA) carries the DNA’s instructions from the nucleus to the ribosome.

• Ribosomal RNA (rRNA) is a key part of ribosomes, which build proteins.

• Transfer RNA (tRNA) brings amino acids to the ribosome to build the protein.

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Multiple Choice

Which type of RNA is responsible for carrying the copied genetic code from the nucleus to the ribosome?

• Messenger RNA (mRNA)

• Ribosomal RNA (rRNA)

• Transfer RNA (tRNA)

• All of the above

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Step 1: Transcription

• Transcription creates an mRNA copy of a DNA gene inside the cell's nucleus.

• The DNA molecule unzips, and an enzyme called RNA polymerase reads the strand.

• It builds mRNA by pairing Adenine (A) with Uracil (U) and Cytosine (C) with Guanine (G).

• The new mRNA strand detaches and travels out of the nucleus to a ribosome.

Multiple Choice

During transcription, if the DNA template strand has the sequence Adenine-Thymine-Guanine (A-T-G), what will the complementary mRNA sequence be?

• U-A-C

• T-A-C

• U-A-G

• A-U-G

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Step 2: Translation

• Translation decodes the mRNA message to build a protein in the cytoplasm.

• ​The ribosome reads the mRNA sequence in three-base groups called codons.

• Transfer RNA (tRNA) brings the specific amino acid for each codon.

• The amino acids are linked into a chain that folds into a protein.

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Multiple Choice

What is the primary role of transfer RNA (tRNA) in the process of translation?

• It carries the genetic code from the nucleus.

• It forms the structure of the ribosome.

• It brings specific amino acids to the ribosome.

• It unzips the DNA double helix.

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Common Misconceptions

Misconception	Correction
DNA leaves the nucleus to make proteins.	DNA stays in the nucleus and sends a copy, called mRNA, out.
The DNA code is read directly to make a protein.	First, transcription creates mRNA, then translation reads the mRNA to build proteins.
DNA and RNA are just different names for the same thing.	They differ in their sugar, bases, and overall structure.

Multiple Choice

Why is it necessary for a cell to use messenger RNA (mRNA) to make proteins instead of using the DNA directly?

• Because mRNA is more stable than DNA and is less likely to have errors.

• Because the ribosomes needed for protein synthesis cannot enter the nucleus.

• To keep the original DNA blueprint safe within the nucleus, preventing potential damage.

• Because DNA contains Uracil, which cannot be read by the ribosomes.

Multiple Choice

If a DNA sequence is C-A-G, which process ensures that the correct amino acid is added to the protein chain?

• The ribosome directly matches the DNA codon C-A-G to an amino acid.

• The mRNA is first transcribed to G-U-C, and then a tRNA with the anticodon C-A-G brings the correct amino acid.

• The DNA is replicated, and the new DNA strand is used to find the amino acid.

• The tRNA directly reads the DNA and brings the corresponding amino acid to the ribosome.

Multiple Choice

If a cell was unable to produce any tRNA molecules, what would be the immediate consequence for protein synthesis?

• DNA would not be able to unzip for transcription.

• mRNA would be unable to travel from the nucleus to the cytoplasm.

• The ribosome would not be able to read the codons on the mRNA strand.

• Amino acids could not be transported to the ribosome to build the protein.

Multiple Choice

Imagine a mutation occurs that prevents the ribosome (rRNA) from functioning. Which of the following outcomes would you predict?

• The cell could not transcribe DNA into mRNA.

• The mRNA message could not be decoded into a protein.

• The DNA would be unable to replicate itself.

• tRNA molecules would be unable to pick up amino acids.

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Summary

• The Central Dogma states information flows from DNA to RNA to protein.

• Transcription copies a gene from DNA into a messenger RNA (mRNA) molecule.

• Translation uses the mRNA code to assemble amino acids into a protein.

• This process protects DNA and efficiently produces proteins needed for life.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1 (Very Confused)

• 2 (A Little Unsure)

• 3 (Confident)

• 4 (Very Confident, I could teach it!)