Chapter 21 Flashcards
(25 cards)
What is the shape and structure of DNA?
Double helix made of two nucleotide strands; each nucleotide = deoxyribose sugar + phosphate + base (A, T, C, G)
DNA consists of two strands that twist around each other, forming a double helix structure.
What is the complementary base-pair rule?
A pairs with T, C pairs with G (via hydrogen bonds)
This rule is essential for DNA replication and the accuracy of genetic information transfer.
What is semi-conservative replication?
Each new DNA molecule keeps one old strand and builds one new strand
This method ensures that each daughter DNA molecule contains one original strand and one newly synthesized strand.
What enzyme is responsible for copying DNA?
DNA polymerase – unzips helix, matches complementary bases, links backbone
DNA polymerase plays a critical role in DNA replication by synthesizing new strands.
What is the Central Dogma of molecular biology?
DNA transcription → mRNA then mRNA translation → protein
This concept describes the flow of genetic information within a biological system.
What are two major differences between RNA and DNA?
Sugar = ribose (not deoxyribose); base U (uracil) replaces T; RNA usually single-stranded
These differences are fundamental to the roles RNA and DNA play in cells.
What is the function of mRNA?
Carries DNA’s message (codons) from nucleus to ribosome
mRNA serves as the template for protein synthesis during translation.
Define a codon.
Three-base ‘word’ on mRNA that codes for one amino acid or a START/STOP signal
Codons are crucial for translating genetic information into functional proteins.
What are the START and STOP codons?
START = AUG (methionine); STOP = UAA, UAG, UGA
These codons signal the beginning and end of protein synthesis.
What are the roles of tRNA?
Has anticodon that pairs with mRNA codon; carries specific amino acid to ribosome
tRNA is essential for translating mRNA into a polypeptide chain.
What is the composition of a ribosome?
rRNA + proteins; two subunits clamp onto mRNA, catalyze peptide bonds
Ribosomes are the cellular machinery that synthesizes proteins.
What are the stages of translation?
1 Initiation (AUG + ribosome) 2 Elongation (amino-acids chain grows) 3 Termination (STOP codon releases protein
Each stage is critical for the accurate synthesis of proteins.
What is a mutation?
Permanent change in DNA sequence; may be substitution, insertion, deletion
Mutations can have various effects on an organism’s phenotype.
What is the effect of point (base-pair) substitution?
May change one amino acid or be silent; impact depends on codon change
The consequences of point mutations can vary widely.
Define frameshift mutation.
Insertion/deletion not in multiples of 3; shifts reading frame, usually ruins protein
Frameshift mutations can lead to significant changes in protein structure and function.
What is epigenetics?
Chemical tags (e.g., methyl groups) that switch genes on/off without altering base sequence
Epigenetic modifications can affect gene expression and are heritable.
What is a restriction enzyme?
Bacterial ‘DNA scissors’ that cut at specific sequences, leaving sticky ends
These enzymes are widely used in genetic engineering and molecular cloning.
What is recombinant DNA?
DNA combined from 2+ sources (e.g., human gene inserted into bacterial plasmid)
Recombinant DNA technology is fundamental to biotechnology and genetic research.
Why is a plasmid useful as a vector?
Circular bacterial DNA replicates independently; can carry and express foreign gene
Plasmids are commonly used in genetic engineering to introduce new genes into organisms.
What is the purpose of PCR?
Polymerase Chain Reaction rapidly amplifies (copies) selected DNA segment in vitro
PCR is a vital technique in molecular biology for analyzing DNA.
Define transgenic organism.
Organism carrying gene(s) from another species; example: pest-resistant corn
Transgenic organisms are used in agriculture and medicine for various applications.
What is the goal of gene therapy?
Insert healthy gene into patient’s cells to replace faulty gene product
Gene therapy holds potential for treating genetic disorders.
Differentiate between genome and epigenome.
Genome = full DNA sequence; Epigenome = reversible tags regulating gene activity
Understanding both concepts is crucial for studying genetics and gene regulation.
What was a key outcome of the Human Genome Project?
Sequenced ~3 billion bases; estimated 20–25 k genes; opened door to personalized medicine
The project has had a profound impact on genetics, medicine, and biotechnology.
