Transcription and Translation + DNA Replication

Comparison between DNA polymerase and RNA polymerase:

Feature	DNA Polymerase	RNA Polymerase
Function	Synthesizes DNA (during replication)	Synthesizes RNA (during transcription)
Template	DNA	DNA
Product	DNA	RNA
Primer Requirement	Needs a primer to start synthesis	Does not need a primer
Base Used	A, T, C, G	A, U, C, G (uses uracil instead of thymine)
Direction of Synthesis	5' to 3'	5' to 3'
Proofreading	Yes (has exonuclease activity to correct errors)	No or minimal proofreading
Location in Eukaryotes	Nucleus (also in mitochondria)	Nucleus (for mRNA, rRNA, tRNA synthesis)
Main Role	DNA replication (copies the entire genome)	Transcription (makes RNA from one gene)

🧬 Transcription (DNA → RNA)

Location: Nucleus

Goal: Make an RNA copy (mRNA) of a gene from DNA

🔧 Key Enzyme: RNA Polymerase

| Function | Binds to the DNA promoter region and builds an mRNA strand by matching RNA nucleotides to the DNA template strand. |

🧷 Supporting Molecules:

• RNA Helicase (optional at TEAS level): Helps unwind DNA so RNA polymerase can access the gene.

• Transcription factors (not always tested on TEAS): Help RNA polymerase bind to the DNA.

🔁 Summary Flow:

1. DNA unwinds → (Helicase may help)

2. RNA Polymerase binds → Starts making mRNA

3. mRNA strand detaches when done

🧬 Transcription (DNA → RNA) Quiz

📝 Multiple Choice & Flashcard Style

1. Where does transcription occur in eukaryotic cells?
   A. Cytoplasm
   B. Ribosome
   C. Nucleus
   D. Mitochondria

   
   → Answer: C. Nucleus

1. What enzyme is responsible for building mRNA from a DNA template?

   
   → Answer: RNA Polymerase

1. What is the name of the DNA region where RNA polymerase binds to begin transcription?

   
   → Answer: Promoter

1. What molecule is the product of transcription?

   
   → Answer: mRNA (messenger RNA)

1. What happens to the DNA molecule during transcription?
   A. It is destroyed
   B. It is translated
   C. It is unwound
   D. It leaves the nucleus

   
   → Answer: C. It is unwound

🧫 Translation (RNA → Protein)

🧫 Translation (RNA → Protein)

Location: Cytoplasm at the ribosome
Goal: Build a protein from the mRNA instructions

🔧 Key Enzymes/Molecules:

Molecule	Function
Ribosome (not an enzyme but essential)	Facilitates matching mRNA codons to tRNA anticodons and links amino acids
Peptidyl transferase (part of the ribosome)	Catalyzes the formation of peptide bonds between amino acids
Aminoacyl-tRNA synthetase	Enzyme that attaches the correct amino acid to each tRNA

🧷 Supporting Players:

• tRNA: Transfers amino acids to the ribosome.

• mRNA: Brings the genetic code from DNA.

• rRNA: Structural and enzymatic part of the ribosome.

🧫 Translation (RNA → Protein) Quiz

🧫 Translation Questions (mRNA → Protein)

1. Where does translation occur in the cell?

   
   → Answer: At the ribosome in the cytoplasm

1. What type of RNA carries amino acids to the ribosome?

   
   → Answer: tRNA (transfer RNA)

2. What is the three-base sequence on mRNA called?

   
   → Answer: Codon

3. What is the start codon for protein synthesis?

   
   → Answer: AUG

1. What does a stop codon do during translation?

   
   → Answer: Signals the ribosome to end protein synthesis

1. What type of bond forms between amino acids in a growing protein

   chain?

   
   → Answer: Peptide bond

2. What molecule reads the codons on mRNA and assembles the protein?

   
   → Answer: Ribosome

🧠 TEAS Tip: What You Should Definitely Know

🔧 Enzyme & Molecule Function Questions

1. Which enzyme is responsible for copying DNA into RNA?
   → Answer: RNA Polymerase

2. Which enzyme links amino acids together during translation?
   → Answer: Peptidyl Transferase

3. Which enzyme attaches amino acids to tRNA?
   → Answer: Aminoacyl-tRNA Synthetase

4. What molecule acts like an enzyme and is part of the ribosome?
   → Answer: rRNA (ribosomal RNA)

5. True or False: RNA Polymerase is used in both transcription and translation.
   → Answer: False (Only transcription)

6. Which of the following is NOT involved in transcription?
   A. RNA Polymerase
   B. mRNA
   C. Ribosome
   D. DNA
   → Answer: C. Ribosome

✅ RNA Polymerase = main enzyme for transcription
✅ Ribosome = main site for translation
✅ tRNA = brings amino acids
✅ Peptide bonds are formed between amino acids
✅ Codons (3-base sequences) on mRNA code for amino acids

🌟 Summary Table of Enzymes

Process	Enzyme/Molecule	Function
Transcription	RNA Polymerase	Builds mRNA from DNA
Transcription	(Helicase)	Unwinds DNA (optional detail for TEAS)
Translation	Peptidyl transferase	Forms peptide bonds between amino acids
Translation	Aminoacyl-tRNA synthetase	Loads tRNA with the correct amino acid
Translation	Ribosome (with rRNA)	Coordinates the process (acts like an enzyme)

DNA Replication – Key Facts for TEAS

Feature	Description

Location

Nucleus

Purpose

To make an exact copy of DNA before cell division

End result

Two identical DNA molecules (each with one old strand and one new strand – called semi-conservative)

DNA Replication Enzymes — In the Sequence They Happen

1. Topoisomerase

   (top·o·i·som·er·ase

   /ˌtäpōˌīˈsäməˌrās/)

   • Function: Relieves twisting tension and prevents supercoiling ahead of the replication fork by cutting and rejoining the DNA.

   • 📍Acts first, before the helix is unwound.

2. DNA Helicase

   • Function: Unzips the DNA double helix by breaking the hydrogen bonds between base pairs, forming the replication fork.

3. Single-Strand Binding Proteins (SSBs)

   • Function: Bind to the separated DNA strands to keep them open and stable, preventing them from re-pairing.

4. Primase

   • Function: Adds a short RNA primer to the DNA strand to give DNA polymerase a starting point.

5. DNA Polymerase

   • Function: Adds new complementary DNA nucleotides to the template strand in the 5' to 3' direction.

   • Builds the leading strand continuously and the lagging strand in fragments (Okazaki fragments).

6. DNA Ligase

   • Function: Seals the gaps between Okazaki fragments on the lagging strand, forming a continuous strand.

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🧠 Quick Summary Table (In Order)

Step	Enzyme/Molecule	Role
1	Topoisomerase	Prevents DNA supercoiling ahead of the fork
2	Helicase	Unwinds and separates the DNA strands
3	SSBs	Stabilize separated DNA strands
4	Primase	Adds RNA primer
5	DNA Polymerase	Synthesizes new DNA strands
6	DNA Ligase	Joins DNA fragments (especially on lagging strand)

DNA Replication Practice Questions

🧠 TEAS Practice Questions

1. What is the main enzyme that adds new nucleotides to the growing DNA strand?
→ ✅ DNA Polymerase

2. What enzyme unzips the DNA double helix?
→ ✅ Helicase

3. Why is a primer needed in DNA replication?
→ ✅ DNA Polymerase needs a starting point to begin adding nucleotides

4. Which strand is built in fragments during replication?
→ ✅ Lagging strand

5. What enzyme seals the fragments together?
→ ✅ DNA Ligase

6.What does Topoisomerase do in the process of DNA replication?

→ Relieve tension ahead of the replication fork due to the supercoiling nature of the double helical DNA.