Higher Biology - Unit 1 DNA in the Genome

Key Area 3: Gene Expression

What is Gene Expression?

• Process of using information from a gene to synthesize proteins through protein synthesis.
• Genotype: Sequence of bases in genes.
• Phenotype: The physical appearance determined by proteins made from gene expression.

Overview of Protein Synthesis

1. DNA in the nucleus is transcribed to mRNA.
2. mRNA travels to ribosome where it is translated into proteins.

Stages of Protein Synthesis

1. Transcription - occurs in the nucleus.

   • Involves synthesizing mRNA from DNA.
   • Enzyme RNA polymerase unwinds DNA and breaks hydrogen bonds.
   • Complementary base pairing occurs (A-U, C-G).
   • Ends with a stop codon which signals the end of transcription.
   • Result: Primary transcript of mRNA.

2. Translation - occurs at the ribosome.

   • Involves synthesizing proteins from mRNA.
   • Starts with the start codon (AUG) and ends with a stop codon.
   • tRNA brings specific amino acids to the ribosome corresponding to mRNA codons.
   • Peptide bonds form between amino acids to create proteins (polypeptides).
   • Proteins fold into specific 3D shapes held together by hydrogen bonds.

Differences Between DNA and RNA

• Structure: DNA is double-stranded; RNA is single-stranded.
• Sugar: DNA contains deoxyribose; RNA contains ribose.
• Bases: DNA uses thymine (T), while RNA uses uracil (U).

Types of RNA

1. mRNA (Messenger RNA): Carries genetic code from nucleus to ribosome.
2. tRNA (Transfer RNA): Carries specific amino acids to ribosome.
3. rRNA (Ribosomal RNA): Makes up the ribosome.

Introns and Exons

• Introns: Non-coding regions of mRNA that are removed.
• Exons: Coding regions that are spliced together to form mature mRNA.
• RNA Splicing: The process of removing introns and joining exons to form mature mRNA.
• Same primary mRNA can lead to different proteins by splicing different exons/introns.

Summary of Processes

1. Transcription:

   • Gene copied into mRNA by RNA polymerase.
   • Primary mRNA transcript is spliced to mature mRNA in nucleus.

2. Translation:

   • Mature mRNA attaches to ribosome.
   • tRNA brings anticodons and amino acids.
   • Peptide bonds form to create proteins at ribosome.

Conclusion

• Genetic information is translated into functional proteins through transcription and translation.
• Quiz will be provided to reinforce knowledge.