Genetics: Types of Mutations Quiz

BIOL 217 Topic 11 - Gene Expression

• Gene expression is the process where information encoded in genes are used to create proteins, leading to observable traits (phenotypes).
• This process occurs through transcription and translation.
• DNA is inherited, and its sequence (genotype) dictates the proteins that are made
• Proteins determine the phenotype.
• Gene expression is influenced by environmental factors.

Learning Objectives

• Understand the central dogma, the genetic code, and information flow from gene to protein.
• Compare and contrast transcription and translation.
• Explain the steps in transcription (initiation, elongation, termination) and the roles of key molecules (RNA polymerase).
• Understand different types of mutations and their impact on proteins.

The Flow of Genetic Material

• DNA holds the genetic information for traits.
• This information is in specific nucleotide sequences.
• Proteins link genotype to phenotype.
• Gene expression involves two steps: transcription and translation.

Principles of Gene Expression

• RNA acts as a bridge between genes and proteins.
• Transcription synthesizes RNA using information in DNA. Messenger RNA (mRNA) is a product.
• Translation synthesizes a polypeptide, using information in mRNA. Ribosomes are the sites of action.

Principles of Gene Expression (Prokaryotes)

• Prokaryotic mRNA can be translated before transcription is complete.
• Transcription and translation occur in the cytoplasm.

Principles of Gene Expression (Eukaryotes)

• Nuclear envelope separates transcription in the nucleus and translation in the cytoplasm.
• Eukaryotic RNA transcripts undergo processing before translation.

Central Dogma

• The central dogma shows the unidirectional flow of genetic information: DNA → RNA → Protein.
• This is a fundamental concept showing how cells control gene expression.

The Genetic Code

• The genetic code comprises three-nucleotide words (codons).
• The codons specify particular amino acids.
• The code is non-overlapping and is nearly universal.

The Flow of Information

• Template strand (3' to 5') provides a template for the complementary mRNA.
• Non-template strand (5' to 3') is identical to mRNA codons (with U replacing T).

The Flow of Information (Translation)

• During translation, mRNA codons are read in the 5' to 3' direction.
• Each codon specifies a particular amino acid. This produces a polypeptide.

Universal Genetic Code

• The genetic code is nearly universal, shared by all life forms.
• Introduced genes can be expressed in foreign species.

Transcription (Stages)

• Initiation: RNA polymerase binds to a promoter region.
• Elongation: RNA polymerase moves along the DNA, synthesizing RNA.
• Termination: RNA polymerase encounters a terminator sequence and detaches.

Transcription (RNA Polymerase)

• RNA polymerase catalyzes RNA synthesis.
• This process follows the base-pairing rules of DNA, but with uracil (U) in RNA instead of thymine (T).

Transcription (Promoter)

• Promoter: DNA sequence where RNA polymerase attaches.
• Terminator: sequence signaling the end of transcription.
• Transcription unit: the stretch of DNA that is transcribed.

Synthesizing an RNA Transcript (Initiation)

• Promoters are transcriptional start points, extending upstream from the start point, including the TATA box (crucial in eukaryotes for initiation complex).
• Transcription factors mediate RNA polymerase binding and start of transcription.
• Transcription initiation complex is a completed assembly of transcription factors and RNA polymerase II bound to the promoter.

Synthesizing an RNA Transcript (Elongation)

• RNA polymerase untwists DNA and adds nucleotides to the 3' end of the growing RNA strand.
• Transcription proceeds at ~40 nucleotides/second in eukaryotes.
• Multiple RNA polymerases can transcribe a gene simultaneously.

Synthesizing an RNA Transcript (Termination)

• Termination mechanisms vary between bacteria and eukaryotes.
• In bacteria, polymerase stops at the terminator sequence.
• In eukaryotes, polymerase transcribes a polyadenylation sequence, and the RNA is released.

Translation

• Translation is the process of converting mRNA information into a polypeptide.
• The genetic code is crucial in determining amino acid sequence.

Molecular Components in Translation

• Transfer RNA (tRNA) acts as an adaptor, bridging between codons and amino acids in translation.
• Transfer RNA carries a specific amino acid to the ribosome.
• tRNA contains an anticodon that is complementary to the mRNA codon.

3D Structure of tRNA

• tRNA has an L-shape with two ends (5′ and 3′) located close to one end.
• The 3′ end specifically attaches to the amino acid.

Accurate Translation (Steps)

• tRNA and amino acid are correctly matched by aminoacyl-tRNA synthetase.
• The tRNA anticodon correctly matches mRNA codons.

Ribosomes

• Ribosomes facilitate coupling of tRNA anticodons with mRNA codons in protein synthesis.
• Ribosomes are made of ribosomal RNA (rRNA) and proteins.
• Ribosomes include A, P, and E sites for tRNA binding.

Ribosomal Binding Sites

• A-site: holds tRNA bringing the next amino acid.
• P-site: holds tRNA carrying the growing polypeptide.
• E-site: exit site for tRNA after peptide transfer.

Building a Polypeptide

• Translation involves three stages: initiation, elongation, and termination.
• Energy is required for these steps.
• Factors assist each stage.

Mutations

• Mutations are changes in DNA sequence.
• Mutations can be beneficial, harmful, or neutral.
• Mutations can affect protein structure and function.

New Mutations and Mutagens

• Spontaneous mutations occur during DNA replication, recombination, or repair.
• Mutagens are physical or chemical agents that can cause mutations.

DNA Mutations (Point Mutations)

• Point mutations are changes in a single nucleotide pair.
• Single nucleotide-pair substitutions (silent, missense, nonsense) are common types.

Nucleotide-Pair Substitution (Types)

• Silent mutations: have no effect on the amino acid.
• Missense mutations: change the amino acid.
• Nonsense mutations: change a codon into a stop codon, frequently causing a non-functional protein.

Test your knowledge on different types of mutations in genetics with this engaging quiz. Explore silent and nonsense mutations, point mutations, and the causes of spontaneous mutations. Perfect for students studying genetics and molecular biology.