Cell Cycle and Protein Synthesis

4.2 Protein Synthesis

Exploring the journey from DNA to protein

Unlocking DNA Replication

• DNA replication is the process by which a cell makes an identical copy of its DNA.
• It occurs during the S phase of the cell cycle.
• Key enzymes, such as DNA polymerase, unwind the DNA double helix and synthesize new strands.
• The process is highly accurate, with an error rate of about one in a billion base pairs.
• Understanding DNA replication is crucial for studying genetic diseases and developing new treatments.

DNA Polymerase

DNA Polymerase is the key enzyme involved in DNA replication. It synthesizes new DNA strands by adding nucleotides to the existing template strands. It also proofreads and repairs errors in the newly synthesized DNA. Without DNA Polymerase, accurate replication of DNA would not be possible.

Multiple Choice

What is the key enzyme involved in DNA replication?

• Helicase

• RNA polymerase

• DNA ligase

• DNA polymerase

RNA Structure

• RNA is like DNA in that it is a nucleic acid, however it has several structural differences:

  • RNA is a single strand 

  • RNA contains ribose as its sugar

  • RNA contains nitrogenous base uracil instead of thymine

RNA’s main job is to provide the instructions to build a protein 

Draw

Draw the structure of RNA and label the components.

Open Ended

What makes RNA different from DNA?

Types of RNA

• mRNA (messenger RNA): carries the genetic information from DNA, in the nucleus, to the ribosomes for protein synthesis.

• tRNA (transfer RNA): brings amino acids to the ribosomes during protein synthesis.

• rRNA (ribosomal RNA): forms the structure of ribosomes and catalyzes protein synthesis.

mRNA - The Messenger

mRNA carries the genetic information from DNA to the ribosomes for protein synthesis. It acts as a messenger between the two, ensuring that the correct proteins are produced. Without mRNA, the process of protein synthesis would not be possible.

Multiple Choice

Which type of RNA carries the genetic information from DNA to the ribosomes for protein synthesis?

• mRNA

• tRNA

• rRNA

• sRNA

Transcription: DNA to RNA

• Transcription is the process by which an RNA molecule is synthesized from a DNA template.
• It occurs in the nucleus of eukaryotic cells and the cytoplasm of prokaryotic cells.
• RNA polymerase binds to the DNA and separates the two strands.
• One of the DNA strands serves as a template for RNA synthesis.
• The RNA molecule is complementary to the DNA template strand.
• The resulting RNA molecule is called messenger RNA (mRNA).

Transcription in Eukaryotic Cells

• 1. RNA polymerase binds to sites called promoters. These are places that have a certain base sequence. 

• 2. RNA polymerase unzip the DNA and begin adding complementary bases to make a mRNA strand. 

  • This is very similar to replication, except that the T’s are replaced with U’s.

Every three base pairs are known as a codon and are used in the next process; translation. These codons each code for a particular amino acid.

Transcription Video

Multiple Choice

Where does transcription occur in eukaryotic cells?

• Nucleus

• Cytoplasm

• Mitochondria

• Endoplasmic Reticulum

Transcription Continued

• Not all nucleotides in DNA carry instructions for making a protein, therefore RNA must edit it’s copy.

  • Introns = portions of the RNA strand that are not intended for coding

  • Exons = regions of the RNA that does carry instructions

• 3. The introns are removed from the mRNA and the strand is fused back together 

4. The mRNA then leaves the nucleus and travels to the cytoplasm

Open Ended

List the steps to Transcription. What is the end result of Transcription? Where does the process go after Transcription?

Translation

• DNA transcribed to mRNA and mRNA then turns helps “translate” it’s message into a protein.

• A code is needed to convert this message:

  • There are 20 common amino acids 

  • A group of three nitrogenous bases in mRNA code for one amino acid. This group of three is called a codon.

  • Not all codons are instructions. There are start and stop codons also. 

  • All living things have these same amino acid possibilities. This is a big idea behind evolution.

Translation Continued

• 1. As the mRNA is read in the ribosome, each codon is matched with a tRNA’s anticodon.

  • Codon = AAA Anticodon = UUU

• 2. The tRNA brings the correct amino acid in because it reads the codon.

• 3. tRNA “drops off” the amino acid and the  next codon is read

• Eventually all the amino acids will create a polypeptide chain and then a protein 

• When a stop codon has been read it will detach and leave for the appropriate body section.

Protein Synthesis Video

Translation Video

Draw

Draw the process of Protein synthesis. Start with Transcription and end with Translation.

Open Ended

Finish the complimentary strand of DNA. Then transcribe to mRNA. Use the codon chart to list the proteins the strand will make.

TAC-CCG-TCG-AAT-ATT