14.2 Ribososmes and Protein Synthesis

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14.2 Ribosomes and Protein Synthesis

Grade: 9

Course Name: Biology

Today’s topic

14.2 Ribosomes and Protein Synthesis

Standard: HS-LS1-1 / HS-LS3-1

• 14.2 Ribosomes and Protein Synthesis

**Remember to reflect on the success criteria (WILF) at the end of the lesson

• 14.2 Ribosomes and Protein Synthesis

• 14.2 Ribosomes and Protein Synthesis

Protein Mystery Code

AUG – UUU – GGC – UAA

👉 “This is a message… but can you understand it?”

Think-Pair-Share

Discuss:

• What could this code represent?

• Why is it written in groups of 3?

Connection:

👉 “This is how your body reads instructions to build proteins.”

Question:

“How does the cell translate this code into something useful like muscle, enzymes, or hair?”

Transition:

👉 “Today, we’ll uncover how ribosomes act like ‘machines’ that translate this code into proteins.”

• 14.2 Ribosomes and Protein Synthesis

Explain how ribosomes translate mRNA codons into amino acids to build proteins and determine their structure and function.

1. mRNA sequence

AUG – UUU – GGC – UAA

2. Decode

• Decode each codon into an amino acid.

• Write the amino acid sequence.

3. Answer

• What tells the ribosome where to start and stop?

• Why is the order important?

Transition:

👉 “Now that you decoded the message, let’s see how the ribosome actually builds this protein step by step.”

• 14.2 Ribosomes and Protein Synthesis

• 14.2 Ribosomes and Protein Synthesis

The Genetic Code

• Transcription is the first step in the process of decoding genetic messages (copying of nucleotide base sequence from DNA to RNA).

• The second step led to the assembly of the protein.

• Proteins are made by joining amino acids together into chains called polypeptides.

• We have 20 different amino acids.

• The specific order in which amino acids are joined together in a polypeptide chain determines the shape, chemical properties, and function of a protein.

Question: How is the order of bases in DNA and RNA molecules translated into the order of amino acids in a polypeptide?

• 14.2 Ribosomes and Protein Synthesis

The Genetic Code

• The four bases of RNA form a kind of language with just four letters: A, C, G, and U. We call this language the genetic code.

Question: How can a code with just four letters carry the instructions for 20 different amino acids?

• The genetic code is read in groups of three bases.

• Each word of the code is three bases long and corresponds to a single amino acid.

• This three-base word is known as a codon.

A codon consists of three consecutive bases that specify a single amino acid to be added to the polypeptide chain.

• 14.2 Ribosomes and Protein Synthesis

• 14.2 Ribosomes and Protein Synthesis

• There are four different bases in RNA, so there are possible three-base codons (4 x 4 x 4 = 64) in the genetic code.

• Most amino acids can be specified by more than one codon.

Example: Six different codons (UUA, UUG, CUU, CUC, CUA, and CUG) specify leucine.

But only one codon (UGG) specifies the amino acid tryptophan.

How to Read Codons?

• 14.2 Ribosomes and Protein Synthesis

How to Read Codons?

• 14.2 Ribosomes and Protein Synthesis

• 14.2 Ribosomes and Protein Synthesis

Quick Assessment:

mRNA sequence: AUG – GCU – UAC – GGA – UAA

Questions:

• Write the amino acid sequence.

Identify:

Start codon: __________

Stop codon: __________

⚡ Concept Check

What is the role of the ribosome?
☐ Makes DNA
☐ Builds proteins
☐ Breaks down food

• What happens if the codons are read incorrectly?

• 14.2 Ribosomes and Protein Synthesis

Thank You

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