science

James Watson and Francis Crick

The two men who discovered that DNA was a double helix.

Nitrogenous bases

Adenine (A) - Thymine (T), Cytosine (C) - Guanine (G).

Components of a nucleotide

Phosphate group, 5-carbon sugar (deoxyribose), nitrogenous base.

Antiparallel DNA strands

The two strands run in opposite directions (5′ → 3′ and 3′ → 5′).

Rosalind Franklin's contribution

She took X-ray diffraction images (Photo 51) that showed DNA's helical shape.

DNA length in human cells

The amount of DNA in a human cell is approximately 6 feet.

Chromosome numbers

The number of chromosomes in a somatic cell of a human is 46; in a gamete, it is 23.

Karyotype analysis

To detect chromosomal abnormalities (like extra or missing chromosomes).

Autosomes vs. sex chromosomes

Autosomes: 44 in somatic cells, 22 in gametes; Sex chromosomes: 2 in somatic cells (XX or XY), 1 in gametes (X or Y).

Procedures for karyotyping

Amniocentesis or chorionic villus sampling (CVS).

Down syndrome

Trisomy 21 - person has 3 copies of chromosome 21 (47 chromosomes total).

Dog chromosome numbers

Your dog has a diploid number of 78, so he would have 78 chromosomes in skin cells and 39 in sperm cells.

Human somatic cells

In somatic cells of a human: 44 autosomes and 2 sex chromosomes.

Human Genome Project

The large-scale project started in 1990 to identify all genes in human cells.

Roles of enzymes in DNA replication

Helicase: Unwinds DNA; DNA polymerase: Adds nucleotides; Ligase: Joins Okazaki fragments.

Complementary mRNA

If DNA reads A-T-G-C, the complementary mRNA is: U-A-C-G.

Point mutation vs. frameshift mutation

Point: Single base change; Frameshift: Insertion or deletion that shifts the reading frame.

Differences between RNA and DNA

RNA is single-stranded; RNA has uracil, DNA has thymine; RNA contains ribose, DNA contains deoxyribose.

Types of RNA

mRNA: Carries code from DNA; tRNA: Brings amino acids; rRNA: Forms part of the ribosome.

Roles of promoter and RNA polymerase

Promoter: Start site on DNA; RNA polymerase: Synthesizes RNA.

RNA editing

Introns are removed, exons are spliced together.

Codon

A codon is a 3-base mRNA sequence that codes for an amino acid.

Anticodon

A 3-base sequence on tRNA that pairs with mRNA codon.

Building blocks of proteins

The building blocks of proteins are called amino acids, connected by peptide bonds.

Role of the ribosome

Assembles proteins by reading mRNA.

Types of mutations

Insertion: Extra base added; Deletion: Base removed; Substitution: One base replaced with another.

Circular genetic code chart

Used to match mRNA codons to amino acids (start from center and move outward).

Bases in a codon

3

Amino acids on tRNA

1

Transcription and translation locations

Transcription occurs in the nucleus; translation occurs in the cytoplasm/ribosome.

Transcription

The process of making RNA from DNA.

Translation

The process of assembling a protein from RNA.

Meiosis vs. mitosis

Meiosis produces 4 genetically different haploid cells; mitosis produces 2 identical diploid cells.

Oogenesis

Produces 1 ovum and 3 polar bodies.

Polar bodies

Usually degenerate and die.

Spermatogenesis

Produces 4 sperm cells.

Crossing over

The exchange of genetic material between homologous chromosomes during Prophase I.

Genetic variation

Increases a population's ability to adapt to changing environments.

Meiosis I

Reduces the amount of genetic material by 50%.

Meiosis II

Reduces the amount of genetic material by 0% (it separates sister chromatids, not chromosome number).

Fertilization

Occurs in the fallopian tube (oviduct) and forms a zygote which develops into an embryo.

Gametes

The only type of cell produced by meiosis (sperm and egg cells).

Sources of genetic variation in meiosis

Crossing over (Prophase I), Independent assortment of chromosomes (Metaphase I), Random fertilization.

End of Meiosis I

2 cells, each with 23 chromosomes (still duplicated).

End of Meiosis II

4 cells, each with 23 chromosomes (unduplicated, haploid).

Anaphase I

Homologous chromosomes separate.

Anaphase II

Sister chromatids separate.

Cystic fibrosis inheritance

If both parents are heterozygous (Ff × Ff): 25% FF (normal), 50% Ff (carrier), 25% ff (affected).

Widow's Peak

Dominant trait (W); Cross: Ww × ww results in 50% Ww (widow's peak), 50% ww (no widow's peak).

Law of Segregation

One gene per trait from each parent (Total of 2 genes for most traits).

Hemophilia inheritance

Mother: XʜX (carrier), Father: XʜY (normal); 50% of sons may have hemophilia; daughters may be carriers.

Colorblind inheritance

Mother: XᴺXᴺ (normal), Father: XᶜY (colorblind); No child will be colorblind, but all daughters will be carriers.

Males and X-linked disorders

Males only have one X chromosome, so one recessive allele causes the disorder.

Pedigree

A diagram that shows the occurrence of a genetic trait in several generations of a family.

Fly genotypes and phenotypes

XᴿXʳ → Female, Red; XᴿY → Male, Red; XʳXʳ → Female, White; XᴿXᴿ → Female, Red; XʳY → Male, White.

Punnett Square results

Cross: White-eyed female (XʳXʳ) × Red-eyed male (XᴿY) results in 50% XᴿXʳ (Female, red-eyed carriers) and 50% XʳY (Male, white-eyed).

Brain functions

Cerebrum: Controls thinking, memory, voluntary movements, and sensory processing; Cerebellum: Coordinates balance and fine muscle movements; Brainstem: Controls involuntary actions like breathing and heart rate.

Brainstem

Controls involuntary actions like breathing and heart rate.

Hypothalamus

Regulates hunger, thirst, body temperature, and hormones.

Thalamus

Acts as a relay station for sensory information.

Medulla oblongata

Controls vital functions like heart rate and breathing.

Central Nervous System (CNS)

Brain and spinal cord; processes information.

Peripheral Nervous System (PNS)

All nerves outside the CNS; connects CNS to the rest of the body.

Somatic

Controls voluntary movements of skeletal muscles.

Autonomic

Controls involuntary functions (e.g., heart rate, digestion).

Sympathetic

"Fight or flight" response; increases heart rate, dilates pupils.

Parasympathetic

"Rest and digest" response; slows heart rate, stimulates digestion.

Sensory (afferent)

Carries signals to the CNS from sensory receptors.

Motor (efferent)

Carries signals from the CNS to muscles and glands.

Reflex

Involuntary and immediate; processed in the spinal cord, not the brain.

Normal response

Slower; involves processing by the brain.

Dendrites

Receive incoming signals.

Cell body (soma)

Contains the nucleus and organelles.

Axon

Transmits electrical impulses away from the cell body.

Myelin sheath

Insulates the axon; speeds up impulse transmission.

Axon terminals

Release neurotransmitters to signal the next cell.

Depolarization

Sodium (Na⁺) channels open; Na⁺ rushes in, making inside positive.

Repolarization

Potassium (K⁺) channels open; K⁺ moves out, restoring negative charge.

Resting potential

Restored by sodium-potassium pump (3 Na⁺ out, 2 K⁺ in).

Action potential

Triggers release of neurotransmitters into the synaptic cleft.

Antibiotics

Kill or inhibit the growth of bacteria by targeting their cell walls, protein synthesis, or DNA replication—without harming human cells.

Fever

Helps the body fight infection by slowing the growth of pathogens and enhancing the immune response.

Nonspecific defenses

Include skin, mucous membranes, inflammation, fever, phagocytic white blood cells (e.g., macrophages), and interferons (proteins that interfere with viruses).

Skin

Acts as a physical barrier to prevent pathogens from entering the body.

Active immunity

Antibodies are produced by the body's own B cells after exposure to a pathogen or a vaccine.

Antigens

Foreign proteins on pathogens that trigger the immune system to respond and produce specific antibodies.

HIV transmission fluids

Blood, Semen, Vaginal fluids, Breast milk.

Cell-mediated immunity

Involves T cells destroying infected or abnormal body cells.

Humoral immunity

Involves B cells producing antibodies that attack pathogens in body fluids.

Antibody binding sites

A typical antibody has two binding sites.

Edward Jenner

Developed the first vaccine by injecting cowpox virus into a boy, who then became immune to smallpox.

Memory cells

Recognize the antigen faster and mount a quicker, stronger immune response, often preventing illness entirely.