🔬General Biology I Unit 16 – Gene Expression

Key Concepts and Terminology

• Gene expression the process by which genetic information encoded in DNA is converted into functional products, such as proteins
• Central dogma of molecular biology describes the flow of genetic information from DNA to RNA to proteins
• Transcription the process of synthesizing RNA from a DNA template
• Translation the process of synthesizing proteins using the genetic information in mRNA
• Regulatory elements sequences of DNA that control gene expression (promoters, enhancers, silencers)
• Mutations changes in the DNA sequence that can affect gene expression and protein function
  • Point mutations single nucleotide changes (substitutions, insertions, deletions)
  • Frameshift mutations insertions or deletions that alter the reading frame of the genetic code
• Epigenetics heritable changes in gene expression that do not involve alterations to the DNA sequence itself

DNA Structure and Function

• DNA (deoxyribonucleic acid) the genetic material that carries the instructions for life
• Double helix structure two complementary strands of nucleotides wound around each other
  • Nucleotides building blocks of DNA, consisting of a sugar (deoxyribose), a phosphate group, and a nitrogenous base
  • Four nitrogenous bases adenine (A), thymine (T), guanine (G), and cytosine (C)
• Complementary base pairing A pairs with T, and G pairs with C through hydrogen bonds
• Antiparallel strands the 5' end of one strand aligns with the 3' end of the other strand
• DNA replication the process of creating an identical copy of the DNA molecule before cell division
• Genes specific sequences of DNA that encode instructions for making proteins or functional RNA molecules

Transcription Process

• Transcription the synthesis of RNA from a DNA template, carried out by RNA polymerase
• RNA polymerase the enzyme responsible for catalyzing the formation of RNA from a DNA template
• Promoter a region of DNA upstream of a gene that initiates transcription and provides a binding site for RNA polymerase
• Transcription factors proteins that bind to specific DNA sequences and regulate the initiation of transcription
• Transcription initiation RNA polymerase binds to the promoter and begins synthesizing RNA
• Elongation RNA polymerase moves along the DNA template, adding nucleotides to the growing RNA strand
• Termination the process by which transcription is halted, and the newly synthesized RNA is released from the DNA template

RNA Processing and Modification

• Pre-mRNA the initial transcript produced by RNA polymerase, which undergoes processing to become mature mRNA
• 5' cap a modified guanine nucleotide added to the 5' end of the pre-mRNA to protect it from degradation and aid in translation
• 3' poly(A) tail a sequence of adenine nucleotides added to the 3' end of the pre-mRNA to stabilize the molecule and facilitate export from the nucleus
• Splicing the removal of non-coding sequences (introns) and joining of coding sequences (exons) to form mature mRNA
  • Spliceosome a complex of proteins and small nuclear RNAs (snRNAs) that catalyzes the splicing reaction
• Alternative splicing a process by which different combinations of exons can be included in the final mRNA, leading to the production of different protein isoforms from a single gene

Translation and Protein Synthesis

• Ribosome the cellular machinery responsible for synthesizing proteins using the genetic information in mRNA
• tRNA (transfer RNA) adaptor molecules that carry specific amino acids and recognize codons in the mRNA
• Codon a sequence of three nucleotides in mRNA that specifies a particular amino acid or a stop signal
• Anticodon a sequence of three nucleotides in tRNA that is complementary to a specific codon in mRNA
• Translation initiation the small ribosomal subunit binds to the mRNA and recruits the large subunit to form the complete ribosome
• Elongation the ribosome moves along the mRNA, adding amino acids to the growing polypeptide chain based on the codon-anticodon interactions
• Termination the ribosome encounters a stop codon, releasing the newly synthesized protein and dissociating from the mRNA

Regulation of Gene Expression

• Gene regulation the control of gene expression to ensure that the right genes are expressed at the right time and in the right amount
• Transcriptional regulation control of gene expression at the level of transcription initiation
  • Activators proteins that enhance transcription by binding to specific DNA sequences and recruiting RNA polymerase
  • Repressors proteins that inhibit transcription by binding to specific DNA sequences and blocking RNA polymerase
• Post-transcriptional regulation control of gene expression after transcription, including mRNA processing, stability, and translation
  • RNA interference (RNAi) a process by which small RNA molecules (siRNAs or miRNAs) target specific mRNAs for degradation or translational repression
• Chromatin remodeling changes in the packaging of DNA that can affect gene expression by altering the accessibility of genes to transcription factors
• DNA methylation the addition of methyl groups to specific cytosine residues in DNA, which can lead to gene silencing

Genetic Mutations and Their Effects

• Silent mutations changes in the DNA sequence that do not alter the amino acid sequence of the protein due to the redundancy of the genetic code
• Missense mutations point mutations that result in the substitution of one amino acid for another in the protein
• Nonsense mutations point mutations that create a premature stop codon, leading to the production of a truncated protein
• Insertion mutations the addition of one or more nucleotides to the DNA sequence, which can alter the reading frame and disrupt protein function
• Deletion mutations the removal of one or more nucleotides from the DNA sequence, which can also alter the reading frame and disrupt protein function
• Chromosomal aberrations large-scale changes in the structure or number of chromosomes (translocations, duplications, deletions)
• Mutagens agents that can cause mutations in DNA (UV radiation, certain chemicals, viruses)

Applications and Current Research

• Recombinant DNA technology the use of molecular biology techniques to create novel DNA sequences by combining DNA from different sources
• Genetic engineering the deliberate modification of an organism's genome using recombinant DNA technology
  • Genetically modified organisms (GMOs) organisms whose genetic material has been altered using genetic engineering techniques
• Gene therapy the introduction of functional genes into cells to replace defective or missing genes and treat genetic disorders
• CRISPR-Cas9 a powerful genome editing tool that allows for precise modifications of DNA sequences in living cells
• Personalized medicine the tailoring of medical treatments to an individual's genetic profile to optimize therapeutic outcomes and minimize side effects
• Synthetic biology the design and construction of new biological parts, devices, and systems, or the redesign of existing natural biological systems for useful purposes
• Epigenome-wide association studies (EWAS) the study of epigenetic modifications across the genome and their association with specific traits or diseases