Molecular Biology, Genetics, and Evolution Vocabulary

Flashcards covering key vocabulary terms related to molecular biology, genetics, and evolution.

DNA Replication

Semi-conservative process where each new DNA molecule consists of one old (parental) and one new (daughter) strand. Occurs during the S phase of the cell cycle.

Origin of Replication

Where DNA replication begins.

Replication Fork

Y-shaped region where DNA is split into two strands.

Replication Bubble

Formed as DNA unwinds at multiple origins (especially in eukaryotes).

Leading Strand

Synthesized continuously in the 5′ → 3′ direction.

Lagging Strand

Synthesized discontinuously in fragments (Okazaki fragments).

Helicase

Unwinds DNA by breaking hydrogen bonds.

Single-Strand Binding Proteins (SSBPs)

Stabilize separated DNA strands.

Topoisomerase/Gyrase

Relieve supercoiling ahead of the replication fork.

Primase

Adds RNA primers to initiate DNA synthesis.

DNA Polymerase III

Main enzyme that adds nucleotides during DNA replication.

DNA Polymerase I

Replaces RNA primers with DNA.

DNA Ligase

Joins Okazaki fragments on the lagging strand.

Transcription

Process of making RNA from DNA using RNA polymerase. Occurs in the nucleus (eukaryotes) or cytoplasm (prokaryotes).

Initiation (Transcription)

RNA polymerase binds to the promoter on DNA.

Elongation (Transcription)

RNA strand grows (5’ → 3’), RNA polymerase reads DNA template (3’ → 5’).

Termination (Transcription)

RNA polymerase stops at the terminator sequence; RNA is released.

5’ GTP Cap

Protects RNA and helps ribosome binding during translation (eukaryotes).

3’ Poly-A Tail

Adds 50–250 adenines to the 3' end of mRNA; protects RNA from degradation (eukaryotes).

Splicing

Removes introns (noncoding regions) and joins exons (coding regions) in eukaryotic mRNA processing.

Spliceosome

Removes introns from pre-mRNA using snRNA and snRNPs (eukaryotes).

mRNA

Carries genetic code from DNA to the ribosome.

rRNA

Forms the structural component of the ribosome.

tRNA

Brings amino acids to the ribosome for protein synthesis.

snRNA

Involved in RNA splicing (eukaryotes).

miRNA

Regulates gene expression by blocking translation or degrading mRNA.

SRP RNA

Targets proteins to the endoplasmic reticulum (ER).

Primary Transcript

The initial RNA molecule before processing (eukaryotes).

Translation

Protein synthesis from mRNA using ribosomes and tRNA. Occurs in the cytoplasm.

Ribosome

Site of protein synthesis, composed of large and small subunits.

tRNA

Carries amino acids to ribosome; contains anticodon.

Codon

Three-base mRNA sequence specifying an amino acid.

A Site (Ribosome)

Arrival site for tRNA carrying the next amino acid.

P Site (Ribosome)

Holds tRNA with the growing polypeptide chain.

E Site (Ribosome)

Exit site for empty tRNA after amino acid is added to the polypeptide.

Constitutively Expressed Gene

Gene is always "on" unless manually shut off, made at a constant rate.

Inducible Gene

Gene is usually "off" but turned "on" as needed.

Repressible Gene

Gene is usually "on" but can be turned "off" if too much product is present.

Operon

A unit with multiple genes under one promoter (polycistronic mRNA) found in prokaryotes.

Repressor

Binds to the operator to block RNA polymerase, preventing transcription (prokaryotes).

Eukaryotic Gene Regulation

Can occur at chromatin structure, transcription initiation, RNA processing, translation, post-translational modification, and protein degradation.

Histone Acetylation

Loosens chromatin, promoting transcription (eukaryotes).

Histone Deacetylation

Tightens chromatin, blocking transcription (eukaryotes).

DNA Methylation

Prevents transcription; often permanent (example: inactive X chromosome) (eukaryotes).

Enhancers

DNA sequences far from a gene; DNA bending brings them near to initiate transcription (eukaryotes).

Activators

Transcription factors that bind to enhancers to initiate transcription (eukaryotes).

Repressors

Block activators or condense chromatin to inhibit transcription (eukaryotes).

Alternative Splicing

Allows one gene to code for different proteins (eukaryotes).

Ubiquitin

Tags proteins for degradation (eukaryotes).

Proteasomes

Degrade tagged proteins (eukaryotes).

RNA Primer

Provides the starting point for DNA synthesis.

DNA Polymerase

Extends the DNA strand by adding nucleotides to the 3’ end.

Nucleotides (dNTPs)

Building blocks of DNA; dATP, dTTP, dCTP, dGTP.

Telomeres

TTAGGG repeats at the end of linear DNA. postpone the erosion of genes from DNA ends.

Telomerase

Reverse transcriptase that adds TTAGGG repeats to the 3’ end of DNA using its RNA template. Found in germ cells, stem cells, and cancer cells.

PCR (Polymerase Chain Reaction)

In vitro DNA amplification.

Taq Polymerase

A heat-stable DNA polymerase used in PCR.

Restriction Enzymes

Cut DNA at specific recognition sites (usually palindromic sequences).

Sticky Ends

Overhangs created by some restriction enzymes, useful for cloning.

Blunt Ends

Straight cuts created by some restriction enzymes.

CRISPR-Cas9

Genome editing system.

Cas9

A nuclease that cuts DNA in CRISPR-Cas9.

gRNA (Guide RNA)

Directs Cas9 to the specific DNA sequence.

Non-Homologous End Joining (NHEJ)

Error-prone DNA repair mechanism in CRISPR-Cas9, often causing insertions/deletions (knockouts).

Homology-Directed Repair (HDR)

Precise DNA editing using a repair template in CRISPR-Cas9.

Adaptation

Inherited traits that increase fitness.

Mutation

New alleles, source of variation.

Gene Flow

Movement of alleles between populations.

Genetic Drift

Random changes in allele frequencies.

Bottleneck Effect

Sudden population decrease alters allele frequency.

Founder Effect

Small group colonizes new area, altering allele frequency.

Natural Selection

Differential reproductive success.

Allopatric Speciation

Physical separation of populations leading to speciation.

Sympatric Speciation

Speciation in the same location due to reproductive isolation.

Viruses

Non-living infectious agents that are obligate intracellular parasites.

Capsid

Protein coat of a virus made of capsomeres.

Reverse Transcriptase

Enzyme used by retroviruses to convert RNA to DNA.

(+)ssRNA Virus

Viral genome acts directly as mRNA (example: COVID-19).

Retrovirus

RNA genome is converted to DNA and integrated into host DNA using reverse transcriptase (example: HIV).

RT-PCR Test

Reverse transcription PCR, used to detect viral RNA.

Vaccine

Contains weakened or inactive virus (or protein) to trigger antibody production.

Antiviral Medication

Targets specific stages of viral replication.

Viroid

Smallest infectious agents, circular ssRNA that cause plant diseases.

Prion

Infectious proteins – misfolded brain proteins.

Prokaryote

Cell with no nucleus (DNA is in a nucleoid) and no membrane-bound organelles (example: Bacteria, Archaea).

Eukaryote

Cell with true nucleus and membrane-bound organelles (example: plants, animals, fungi).

Peptidoglycan

Substance in bacterial cell walls.

Gram-Positive Bacteria

Bacteria with a thick peptidoglycan layer that retains crystal violet stain.

Gram-Negative Bacteria

Bacteria with a thin peptidoglycan layer and an outer membrane.

Endospores

Dormant, resistant cells formed by some Gram-positive bacteria under stress.

Genetic Recombination

Exchange of DNA between different bacteria.

Transformation (Bacteria)

Uptake of naked DNA from the environment.

Vascular Tissue

Tissue that transports water (xylem) and sugars (pholem) throughout a plant.

Microspores

Male Spores.

Megaspores

Female Spores.

Plant Cuticle

Waxy layer that prevents water loss.

Plant Stomata

Adjustable pores for gas exchange.

Antheridium

Male gametangia.

Archegonium

Female gametangia.

Bryophytes

Nonvascular plants; mosses, liverworts.