Molecular Biology: Proteins, Nucleic Acids, DNA Replication, and Biotechnology

Comprehensive practice flashcards defining key vocabulary across proteins, nucleic acids, historical DNA discoveries, protein synthesis, DNA replication mechanisms, and biotechnology techniques.

Protein

A biological polymer made of amino acid monomers joined by peptide bonds, consisting of more than $50$ amino acids.

Amino Acid

The single unit monomer and building block of proteins.

Polypeptide Chain

A chain formed by $50$ amino acids or fewer joined together.

Contractile Proteins

Proteins such as actin and myosin that slide together to cause muscle contraction for fine movement.

Structural Proteins

Proteins responsible for physical support that make up structures like hair, nails, and collagen.

Protein Folding

The coiling and folding of a polypeptide chain driven by amino acid attractions, which gives a protein or enzyme its specific active site shape and function.

DNA (Deoxyribonucleic Acid)

A double-stranded nucleic acid containing deoxyribose sugar and the nitrogenous bases cytosine, guanine, adenine, and thymine, located in the nucleus, cytoplasm, chloroplasts, and mitochondria.

RNA (Ribonucleic Acid)

A single-stranded nucleic acid containing ribose sugar and the nitrogenous bases cytosine, guanine, adenine, and uracil, found in the nucleus, ribosomes, and cytoplasm.

Rosalind Franklin

A physical chemist who captured the X-ray crystallographic diffraction image Photo 51, providing the critical physical evidence for the structure of DNA.

James Watson and Francis Crick

Scientists who proposed the double helix structure of DNA on 25 February 1953 and later shared the Nobel Prize in Physiology or Medicine.

Maurice Wilkins

The scientist who showed Rosalind Franklin's physical X-ray data to Watson and Crick without permission and later shared the Nobel Prize with them.

Erwin Chargaff

The scientist who discovered complementary base pairing rules stating that the percentage of adenine equals thymine ($\%A = \%T$) and guanine equals cytosine ($\%G = \%C$), establishing that purines always pair with pyrimidines.

Transcription

The first step of protein synthesis occurring in the nucleus, in which a DNA template strand is unwound and copied into mRNA by RNA polymerase.

Translation

The stage of protein synthesis that takes place at the ribosomes, where mRNA sequences are decoded into polypeptide chains.

mRNA (Messenger RNA)

The type of RNA that carries the transcribed genetic code from the nucleus to the ribosomes.

tRNA (Transfer RNA)

The type of RNA that recognizes specific codons and picks up matching amino acids to deliver them during translation.

Codon

A three-base triplet sequence found on the mRNA transcript that codes for a specific amino acid.

Semiconservative Replication

The mechanism of DNA replication in which the two original strands separate to each serve as a template, producing two DNA molecules that each contain one original and one newly synthesized strand.

Conservative Replication

A hypothetical model of DNA replication where the original double helix remains completely intact while creating an entirely new molecule.

Dispersive Replication

A hypothetical model of DNA replication where the original strands break into random segments, resulting in old and new pieces interspersed in every strand.

PCR (Polymerase Chain Reaction)

A laboratory method used to make a large number of copies of a specific gene or DNA section to obtain sufficient samples for sequencing, disease testing, or forensic analysis.

DNA Profiling

A forensic technique used to identify individuals by analyzing unique, variable repetitive DNA patterns to match biological evidence, test paternity, or identify human remains.

Restriction Enzyme

An enzyme used during DNA profiling to cut extracted DNA into specific fragments.

Gel Electrophoresis

A process used in DNA profiling where cut DNA fragments are separated according to size across an agarose gel.

Southern Blotting

The procedure in DNA profiling where separated DNA band patterns are transferred from an agarose gel to a nylon membrane for analysis.

S Phase (Synthesis Phase)

The period within interphase occurring completely before cell division starts, during which DNA replication takes place.

DNA Helicase

The enzyme that unwinds and unzips double-stranded DNA by breaking weak hydrogen bonds between base pairs, forming a replication fork.

Primase

The enzyme that synthesizes a small RNA primer to provide a starting attachment point for DNA polymerase.

DNA Polymerase

The primary builder enzyme that binds to single DNA strands and attaches matching free nucleotides from the nucleoplasm to the template strands.

DNA Ligase

The molecular glue enzyme that seals gaps on the lagging strand together to create a continuous, smooth backbone.

Acellular Microorganism

A biological agent that lacks a cellular structure and independent metabolic machinery, consisting solely of a nucleic acid genome encased within a protein coat.

Capsid

The protective outer protein coat surrounding the viral nucleic acid core.

Peptidoglycan

The rigid polymer consisting of sugars and amino acids that forms the cell wall of eubacteria.

Plasmid

A small, circular, extrachromosomal DNA molecule found in bacteria that replicates independently and can carry genes for antibiotic resistance.

Binary Fission

The form of asexual reproduction in prokaryotes where a single cell replicates its circular chromosome and divides into two genetically identical daughter cells.

Slime Capsule

A thick polysaccharide or gelatinous outer layer present in some bacteria that prevents desiccation and protects against phagocytosis by host white blood cells.

Bacteriophage

A specialized type of virus that specifically infects and destroys bacterial cells.

Chitin

The tough, fibrous nitrogen-rich polysaccharide that forms the structural component of fungal cell walls.

Hypha

A thread-like, branching filamentous structure that represents the primary unit of vegetative growth in multicellular fungi.

Mycelium

The dense, interwoven vegetative mass or network formed by branching fungal hyphae.

Saprotrophic Nutrition

An extracellular feeding mechanism where organisms secrete digestive enzymes onto dead or decaying organic matter and absorb the soluble nutrients.

Plasmodium

The single-celled protozoan parasite transmitted to humans by the bite of an infected female Anopheles mosquito, causing malaria.

Mycobacterium tuberculosis

The rod-shaped, pathogenic bacterium that primarily infects human lungs and causes tuberculosis.

Antibiotic

A chemical compound produced by microorganisms or synthesized artificially that kills or inhibits the growth of bacteria without harming host cells.

Antibiotic Resistance

The adaptive capacity of a bacterial population to survive exposure to a drug that was previously effective against it, often mediated by natural selection or plasmid exchange.

Active Immunity

Immunity developed through direct stimulation of the immune system by an antigen, resulting in the production of specific antibodies and long-lived memory cells.

Passive Immunity

Temporary immunity conferred by receiving pre-formed antibodies from another individual or source without inducing an internal memory cell response.

Vaccine

A biological preparation of weakened, killed, or fragmented pathogens administered to trigger an immune response and generate memory cells without causing the disease.

Nitrogen-Fixing Bacteria

Microbes such as Rhizobium that convert atmospheric dinitrogen ($N_2$) into ammonia or nitrates, making nitrogen accessible to plants.

Gregor Mendel

An Austrian monk regarded as the founder of modern genetics, who deduced the fundamental principles of inheritance by performing controlled hybridization experiments with garden pea plants (Pisum sativum).

Genotype

The specific genetic makeup or combination of alleles present in the chromosomes of an organism for a particular trait.

Phenotype

The observable physical or physiological traits of an organism, produced by the interaction between its inherited genotype and the environment.

Homozygous

Having two identical alleles at a given gene locus on homologous chromosomes (e.g., $TT$ or $tt$).

Heterozygous

Having two different alleles at a given gene locus on homologous chromosomes (e.g., $Tt$).

Chromatin

A complex of genomic DNA wrapped around histone proteins that condenses to form discrete chromosomes during nuclear division.

Allele

One of two or more alternative versions of a gene found at the same corresponding locus on homologous chromosomes.

Dominant Allele

A gene variant that masks the presence of an alternative allele and determines the phenotype in both homozygous and heterozygous conditions.

Recessive Allele

A gene variant whose phenotypic expression is concealed in the presence of a dominant allele, appearing in the phenotype only when homozygous (e.g., $tt$).

Gene Pool

The aggregate of all genes and their alleles present across all individuals in an interbreeding population.

Monohybrid Cross

A genetic mating experiment between two parent organisms that tracks the inheritance and segregation of alleles for a single gene.

Punnett Square

A grid-based diagram utilized to calculate the probable genotypic and phenotypic ratios of offspring resulting from a genetic cross:

| Gametes | T      | t      |
|:-------:|:------:|:------:|
| **T**   | $TT$ | $Tt$ |
| **t**   | $Tt$ | $tt$ |

• Phenotypic ratio: $3:1$ (dominant to recessive)
• Genotypic ratio: $1:2:1$ ($TT:Tt:tt$)

Law of Segregation

Mendel's first law, establishing that the two alleles for each gene separate during gametogenesis in meiosis so that every gamete carries only one allele for each locus:

   Parental Cell: [ Tt ]
             /      \
     Meiosis I & II  Meiosis I & II
           v          v
     Gamete: [ T ]    [ t ]

Law of Independent Assortment

Mendel's second law, establishing that alleles for different, unlinked genes segregate independently of one another during the formation of gametes in meiosis.

Sex Chromosomes

The pair of chromosomes ($23\text{rd}$ pair in humans) that governs the biological sex of an organism, designated as $XX$ in biological females and $XY$ in biological males:

Female (XX):   [ X ]  [ X ]
Male   (XY):   [ X ]  [ Y ]

X-Linked Recessive Inheritance

A pattern of transmission for traits or disorders carried on the $X$ chromosome (e.g., hemophilia, red-green color blindness), manifesting much more frequently in males ($X^a Y$) because they possess only a single copy of the chromosome.

Polygenic Inheritance

The additive control of a single continuous phenotypic trait (such as human height or skin color) by two or more independent pairs of genes.

Gene Mutation

A sudden and permanent alteration in the specific nucleotide base sequence of DNA, resulting in modified mRNA transcripts and potentially altered polypeptides.

Pedigree Chart

A standardized family tree diagram tracing the inheritance pattern of a particular trait or disease through multiple generations:

[ □ ] Normal Male       [ ■ ] Affected Male
[ ○ ] Normal Female     [ ● ] Affected Female
         □ ==== ○   (Parents)
            |
     +------+------+
     |             |
     □             ●
 (Normal Son) (Affected Daughter)

Recombinant DNA Technology

The biotechnology method of isolating a gene from one organism and integrating it into a vector plasmid to produce target proteins such as human insulin:

Human Cell DNA                 Bacterial Plasmid
      |                                |
[Cut with Restriction Enzyme]   [Cut with Restriction Enzyme]
      \                                /
       +---- [DNA Ligase Splicing] ----+
                       |
               Recombinant Plasmid
                       |
             Host Bacterium Culture

Somatic Cell Nuclear Transfer

A reproductive cloning technique where the nucleus of an unfertilized donor egg cell is removed and replaced by a diploid nucleus derived from a somatic cell:

Enucleated Egg Cell  +  Diploid Somatic Nucleus
            \                /
             [Electro-fusion]
                    |
             Embryo Cleavage
                    |
       Surrogate Uterus Implantation
                    |
        Genetically Identical Clone

CRISPR-Cas9

A molecular genome-editing system composed of a custom guide RNA ($\text{gRNA}$) and a Cas9 endonuclease enzyme that induces targeted double-strand breaks at specific complementary DNA sequences:

Target DNA:  5'--[======================]--3'
                  : : : : : : : : : : : :
Guide RNA:        [=====================]--Cas9 Nuclease (Cuts DNA)

Endocrine vs. Exocrine Glands

The structural and functional distinction between glandular secretory mechanisms:

Endocrine Glands:                  Exocrine Glands:
[ Secretory Cells ]                [ Secretory Cells ]
         |                                  |
         v (Ductless)                       v (Via Ducts)
[ Blood Capillary ]                [ Body Surface or Cavity ]
  (e.g., Pituitary, Adrenal)         (e.g., Sweat, Salivary, Pancreatic enzymes)

• Endocrine Glands: Ductless glands that secrete hormones directly into bloodstream capillaries to act on distant target organs.
• Exocrine Glands: Glands with ducts that secrete chemical products onto epithelial surfaces or internal cavities.

Blood Glucose Regulation

The homeostatic negative feedback mechanism controlled by antagonistic hormones from the islets of Langerhans:

         High Blood Glucose
                 |
       [Beta Cells: Insulin]
                 v
  Glucose ---> Glycogen (Liver/Muscle)
                 |
       Normal Glucose Level ($\sim 90\,\text{mg/dL}$)
                 ^
  Glycogen ---> Glucose (Liver)
                 ^
      [Alpha Cells: Glucagon]
                 |
          Low Blood Glucose

• Insulin: Promotes glucose absorption into cells and stimulates glycogenesis.
• Glucagon: Triggers glycogen breakdown (glycogenolysis) in the liver to release glucose into the blood.

Osmoregulation via ADH

The negative feedback loop governing water retention and blood plasma volume:

High Blood Osmolarity / Low Blood Pressure (Dehydration)
                          |
                 [Hypothalamus Receptors]
                          |
              [Posterior Pituitary Gland]
                          |
                   Secretes ADH
                          |
               Acts on Kidney Tubules
                          |
              Increased Water Reabsorption
                          |
     Concentrated Urine & Restored Plasma Volume

• Anti-Diuretic Hormone (ADH): Secreted by the posterior pituitary, it makes the distal convoluted tubules and collecting ducts more permeable to water.

Spermatozoon (Sperm Cell)

The motile, haploid male gamete specialized for swimming to and penetrating the ovum:

         +-----------------+  <-- Acrosome (contains hydrolytic enzymes)
         |  ( Nucleus )    |  <-- Haploid genome ($n = 23$)
         +--------+--------+
                  |           <-- Neck / Centriole
         +--------+--------+
         |  Mitochondria   |  <-- Middle Piece (produces ATP for locomotion)
         +--------+--------+
                  |
                  |           <-- Tail / Flagellum (whip-like microtubule core)
                  |
                  v

Hormonal Control of the Ovarian Cycle

The hormonal cascade regulating follicular growth, ovulation, and luteal maintenance:

[Hypothalamus] ---> GnRH
       |
       v
[Anterior Pituitary] ---> FSH stimulates Follicle Growth
                                 |
                                 v
                      Follicle Secretes Estrogen
                                 |
                  High Estrogen Triggers LH Surge
                                 |
                                 v
                         Ovulation (Day 14)
                                 |
                                 v
                           Corpus Luteum
                                 |
                      Secretes Progesterone
              (Thickens & Vascularizes Endometrium)

Umbilical Cord Circulation

The dual-direction vascular network circulating blood between the placenta and the developing fetus:

      Placenta <=============================> Fetus
                 <--- 2 Umbilical Arteries ---
                 (Deoxygenated blood & metabolic waste)

                 --- 1 Umbilical Vein --->
                 (Oxygenated, nutrient-rich blood)

• 1 Umbilical Vein: Transports oxygen and nutrients from the maternal placenta to the fetus.
• 2 Umbilical Arteries: Carry deoxygenated blood and metabolic waste products from the fetus back to the placenta.

Hormonal Positive Feedback in Parturition

The self-reinforcing endocrine reflex mechanism driving labor contractions during childbirth:

Fetal head pushes against maternal cervix
                   |
                   v
Cervical stretch receptors stimulated
                   |
                   v
Sensory nerve signals reach Hypothalamus
                   |
                   v
Posterior Pituitary releases Oxytocin
                   |
                   v
Myometrium contracts with increased force
                   |
                   +---> (Pushes fetus harder against cervix)

Carrying Capacity ($K$)

The maximum population density an ecosystem can sustainably support over time:

Population (N)
    ^
    |               --- Carrying Capacity (K) ---
    |             / - - - - - - - - - - - - - -
    |            / 
    |    S-curve/ (Logistic Growth)
    |          /  
    |        _/   
    +----------------------------------------> Time (t)

• Environmental Resistance: The combined effect of limiting factors (food scarcity, space limits, disease, predation) that stabilizes growth around carrying capacity ($K$).

Eusociality

The most advanced tier of animal social organization, featuring overlapping adult generations, cooperative brood care, and division of labor:

                     Colony Organization
                              |
            +-----------------+-----------------+
            |                                   |
    Reproductive Caste                  Non-Reproductive Caste
   (Queen & Breeding Males)             (Workers & Soldiers)
            |                                   |
  Sole offspring producers            Foraging, maintenance, nest defense

• Examples include naked mole rats, honeybees, ants, and termites.

Population Limiting Factors

Environmental variables that restrict the expansion and density of a biological population:

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