Introduction to Gene Expression and Protein Synthesis

  • Discussion starts with characterizing the recessive trait as resulting from a nonfunctional or functionally different protein.

Overview of Genetic Code to Protein Production

  • The lecture will detail the mechanics of how genetic code transforms into proteins, crucial for understanding DNA expression.

  • Emphasis on a flow of information represented as a road map from genes to proteins.

Structure of Eukaryotic Cell

  • Description of a eukaryotic cell highlighting the nucleus.

    • Nucleus contains chromatin, which houses DNA in chromosome form.

    • Diagram Notes:

    • Nucleus (represented in blue) contains DNA.

Key Processes in Gene Expression

Steps Overview

  1. Transcription

    • Conversion of DNA into RNA.

    • Occurs in the nucleus.

    • Initial product is pre-mRNA.

  2. RNA Processing

    • Modification of pre-mRNA into mature mRNA.

    • Involves splicing out introns and adding a 5' cap and poly-A tail.

  3. Translation

    • mRNA is read by ribosomes in the cytoplasm to synthesize proteins.

    • Converts RNA language into an amino acid sequence.

  • These three processes (transcription, RNA processing, translation) are critical in the flow from genotype to phenotype.

Transcription Process

  • Definition of Transcription: The process of copying the DNA code into RNA.

  • Location: Occurs in the nucleus.

  • Transcription Steps:

    1. Initiation

    • Begins with the binding of transcription factors to the promoter region, specifically the TATA box.

    1. RNA Polymerase Interaction

    • RNA polymerase binds to the promoter region after transcription factors.

    • RNA polymerase has unzipping capabilities; helicase not required.

    1. Direction of RNA Synthesis

    • RNA is synthesized in a 5' to 3' direction, meaning base addition occurs at the 3' end.

Complementary Base Pairing in Transcription

  • A pairs with U (in RNA), not T.

  • C pairs with G, maintaining the original base pairing in DNA.

RNA Processing

Modifications to Pre-mRNA

  • 5' Cap Addition:

    • A modified guanine that protects the mRNA from degradation and aids in ribosome binding.

  • Poly-A Tail Addition:

    • Consists of numerous adenine nucleotides (referred to as poly-A) at the 3' end for stability.

  • Splicing Introns and Exons

    • Introns (non-coding regions) are removed, leading to a smaller, mature mRNA composed solely of exons (the expressed sequences).

    • Mnemonic to remember: Exons = Expressed.

Translation Process

  • Occurs at ribosomes located in the cytoplasm.

  • Role of mRNA: Provides the sequence for amino acid assembly.

  • Amino Acid Sequence Determination:

    • Sequence specified by the codons in mRNA.

    • Ribosomes translate the mRNA into chains of amino acids, producing proteins.

All of life uses this code. The genetic code, composed of sequences of nucleotides, is the foundation for how organisms develop, function, and reproduce.

MUTATIONS - permanent alterations to the DNA code

During replication, DNA is prone to mutations/errors. If those errors are not corrected,  they can lead to changes in the protein produced, potentially resulting in various effects on the organism, from benign variations to serious genetic disorders.

Mutations are the source of new alleles in a population.

  • As a result, they play a crucial role in evolution by providing the genetic diversity needed for natural selection.

DE NOVO MUTATION - a new mutation that occurs for the first time in an individual, rather than being inherited from a parent. Where this occurs is very important. 

  • somatic cells - the cells that make up most of our mass. (brain cells, liver cells, muscle cells)

  • germ cells - cells that ultimately lead to the creation of gametes. (body cells)

    • Only germ-line mutations are heritable mutations, but it doesn’t always mean they will be

Summary of Key Concepts

  • The central dogma of biology captures the flow from gene (DNA) to protein (amino acids).

  • The processes of transcription, RNA processing, and translation are universally applicable, irrespective of whether the gene represents a dominant or recessive trait.

  • Each step of this transformation plays a distinct and critical role, with various enzymes and factors aiding in the processes.