History of Global Science and Technology Lecture Review

Flashcards covering vocabulary and key concepts from medieval science, technology, and global intellectual history including Byzantium, China, India, the Islamic world, Africa, the Americas, and Europe.

Blending Inheritance

The old (wrong) idea that offspring are a mixture of both parents' traits, like mixing red and white paint to get pink. Disproven by Mendel.

Particulate Inheritance

The correct model: traits are carried by discrete units called genes that stay separate and don't blend. Each parent passes on intact alleles to offspring.

Why Mendel's Results Disproved Blending

When he crossed purple/white flower hybrids, white flowers reappeared in the F2 generation at a 3:1 ratio. You cannot recover a blended-away trait — something else had to be happening.

Pure Breeding / Homozygous

An individual with two identical alleles for a gene. Every offspring shows the same phenotype. Mendel's starting plants were pure breeding.

Phenotype

The visible or observable traits of an organism (e.g. purple flowers, smooth seeds).

Genotype

The specific alleles an organism carries for a gene (e.g. BB, Bb, bb).

Dominant Trait

The trait that appears in 100% of F1 hybrids when two pure-breeding lines are crossed. Masks the recessive trait.

Recessive Trait

The trait that "disappears" in F1 hybrids but reappears in F2 offspring at a 1:4 ratio. Only expressed when two recessive alleles are present.

Gene

A segment of DNA on a chromosome that codes for a particular trait or protein.

Allele

One of two or more versions of a gene. Diploid organisms have two alleles per gene, one from each parent.

Homozygous

Having two identical alleles for a gene (e.g. BB or bb).

Heterozygous

Having two different alleles for a gene (e.g. Bb). Shows the dominant phenotype.

Punnett Square

A diagram used to predict the possible genotypes and phenotypes of offspring when two individuals are crossed.

3:1 Ratio

The phenotypic ratio seen in F2 offspring when two heterozygous individuals are crossed. 3 dominant : 1 recessive.

Mendel's F1 Generation

The first hybrid offspring from crossing two pure-breeding parents. All show the dominant phenotype.

Mendel's F2 Generation

Offspring from crossing F1 hybrids with each other. Show a 3:1 dominant to recessive phenotypic ratio.

Nucleotide

The monomer (building block) of DNA and RNA. Made of: (1) a 5-carbon sugar, (2) a nitrogenous base, (3) one to three phosphate groups.

DNA Structure

A double-stranded molecule of polynucleotides wound into a double helix. Strands run antiparallel and are held together by complementary base pairing.

Complementary Base Pairing in DNA

A pairs with T (adenine-thymine); G pairs with C (guanine-cytosine). This is what holds the two strands of DNA together.

Antiparallel

DNA strands run in opposite directions. One strand runs 5'→3' and the other runs 3'→5'.

5' End

The end of a DNA or RNA strand where the phosphate group is attached to the 5' carbon of the sugar. New nucleotides cannot be added here.

3' End

The end of a DNA or RNA strand where the OH group is on the 3' carbon. New nucleotides are always added to this end.

DNA vs RNA Difference 1

RNA uses uracil (U) instead of thymine (T). So RNA bases are A, U, G, C instead of A, T, G, C. Adenine still pairs with uracil.

DNA vs RNA Difference 2

DNA has deoxyribose sugar (missing one oxygen). RNA has ribose sugar (has that extra oxygen). The "D" in DNA stands for deoxy.

Central Dogma

The flow of genetic information: DNA → RNA → Protein. Information goes one way — you cannot go backwards from protein to DNA.

DNA Role

Stores genetic information. DNA never leaves the nucleus.

RNA Role

Expresses genetic information. RNA makes a copy of the DNA that travels out of the nucleus to be used in protein construction.

mRNA (messenger RNA)

The RNA copy of a gene that travels from the nucleus to the cytoplasm where ribosomes read it to build a protein.

tRNA (transfer RNA)

A looped RNA molecule that brings the correct amino acid to the ribosome during translation. One end has an anticodon; the other end carries the amino acid.

Ribosome

The cellular machine that reads mRNA and assembles the protein. Made largely of RNA (rRNA) and proteins.

RNA World Hypothesis

The hypothesis that before DNA or proteins existed, RNA molecules were the first self-replicating molecules. RNA can both store information AND catalyze reactions.

Ribozyme

An RNA molecule that can catalyze (speed up) chemical reactions, just like a protein enzyme. Discovered in 1982. Key evidence for the RNA world hypothesis.

Why RNA First is Plausible

RNA can store information like DNA AND catalyze reactions like proteins — so it could have served both functions before DNA and proteins evolved.

Closed Loop Problem

DNA needs proteins to replicate; proteins need DNA to be made. RNA solves this because it can do both jobs, breaking the chicken-and-egg paradox.

Why DNA Replication is Necessary - Mitosis

Mitosis produces new body cells for growth and repair. Every new cell needs a full copy of the DNA, so DNA must be copied first.

Why DNA Replication is Necessary - Meiosis

Meiosis produces haploid gametes (sperm/eggs) for sexual reproduction. DNA must be copied before the cell divides.

Semiconservative Replication

Each new DNA molecule keeps one original (old) strand and synthesizes one new strand. The old strand acts as the template.

Why Semiconservative Replication Works

Because of complementary base pairing — A always pairs with T and G always pairs with C — the template strand dictates exactly what the new strand will be.

Helicase

The enzyme that unzips DNA by breaking the hydrogen bonds between base pairs, separating the two strands to expose the template.

Primase

The enzyme that adds a short RNA primer to give DNA polymerase a starting point. DNA polymerase cannot start synthesizing from scratch.

DNA Polymerase

The enzyme that reads the template strand and builds the new complementary DNA strand by adding nucleotides in the 5'→3' direction.

DNA Ligase

The enzyme that joins (glues) Okazaki fragments together on the lagging strand into one continuous DNA strand.

DNA Synthesis Direction

DNA can only be synthesized in the 5'→3' direction. New nucleotides are always added to the 3' end of the growing strand.

Leading Strand

The template strand that runs 3'→5'. Its complement is synthesized continuously in the 5'→3' direction. Easy — DNA polymerase just goes straight through.

Lagging Strand

The template strand that runs 5'→3'. Its complement must be synthesized in short chunks going backwards. This is the difficult strand.

Okazaki Fragments

Short DNA fragments synthesized on the lagging strand because DNA polymerase can only build 5'→3'. Later joined together by DNA ligase.

Complementary DNA Rule

A pairs with T, T pairs with A, G pairs with C, C pairs with G. The new strand runs antiparallel to the template strand.

Gene Regulation

The process by which cells control which genes are turned on or off. Needed because all cells have the same DNA but must make different proteins at different times.

Heterochromatin

Tightly packed chromatin. Genes in heterochromatin are OFF because transcription machinery cannot access them.

Euchromatin

Loosely packed chromatin. Genes in euchromatin are ON and accessible to transcription machinery.

Epigenetic Gene Regulation

Regulation of gene expression through chromatin states (heterochromatin vs euchromatin) that can be inherited by daughter cells without changing the DNA sequence itself.

Transcriptional Gene Regulation

Controlling whether or not an mRNA transcript is made in the first place. The first and most fundamental level of gene regulation.

Post-Transcriptional Gene Regulation

Regulation that occurs after the mRNA has already been made (e.g. alternative splicing, mRNA stability).

RNA Polymerase II

The enzyme responsible for synthesizing mRNA during transcription. It attaches complementary RNA nucleotides to the DNA template strand.

Transcription Factors

Proteins that bind to specific DNA sequences and attract RNA Polymerase II to the correct location to begin transcription.

Enhancers

DNA sequences often far from the gene itself. Transcription factors bind here too to help initiate or regulate transcription.

Promoter Sequence

A specific DNA sequence upstream of the gene where transcription factors bind first to initiate transcription.

Transcription Process Summary

1) DNA unwinds 2) Transcription factors bind promoter 3) RNA Pol II assembles 4) mRNA is synthesized 5'→3' 5) Terminates at stop sequence 6) mRNA is processed 7) mRNA exits nucleus

Template Strand (Non-coding Strand)

The DNA strand that RNA Polymerase reads to build the mRNA. Despite being read, it is called the non-coding strand.

Coding Strand (Non-template Strand)

The DNA strand whose sequence matches the mRNA (except T instead of U). Not read by RNA polymerase but called the coding strand.

Introns

Sections of pre-mRNA that are removed (spliced out) before the final mRNA is made. They do not code for protein.

Exons

Sections of pre-mRNA that are kept and actually encode the protein sequence. "Exons are expressed."

Alternative Splicing

When different combinations of exons are kept to produce different mRNA transcripts from the same gene — one gene can code for multiple proteins this way.

mRNA Processing

After transcription, the pre-mRNA is processed: introns are spliced out, exons are joined, and a cap is added before the mRNA leaves the nucleus.

Transcription vs Translation Location (Eukaryotes)

Transcription occurs in the NUCLEUS. Translation occurs in the CYTOPLASM.

Reading Frame

The way mRNA is read in groups of three nucleotides (codons) starting from the start codon AUG. The grouping of three is the "frame."

Codon

A sequence of three mRNA nucleotides that codes for one specific amino acid. There are 64 possible codons.

Start Codon

AUG — codes for methionine and signals the ribosome to begin translation. All proteins start with methionine.

Stop Codon

UAA, UAG, or UGA — do not code for any amino acid. They signal the ribosome to stop translation and release the protein.

Degenerate Genetic Code

The genetic code is degenerate because 64 codons code for only 20 amino acids — so many amino acids are coded by more than one codon.

Silent Mutation

A mutation where the DNA sequence changes but the amino acid coded for stays the same, because of degeneracy (e.g. CC[any base] still codes for proline).

Frameshift Mutation

Caused by an insertion or deletion of a base (not in multiples of 3). Shifts the entire reading frame downstream, usually destroying the protein's function.

Deletion

Removal of one or more bases from the DNA sequence. If not a multiple of 3, causes a frameshift.

Insertion

Addition of one or more extra bases into the DNA sequence. If not a multiple of 3, causes a frameshift.

Translation Process Summary

1) Ribosome assembles at 5' end of mRNA, scans for AUG 2) tRNA brings methionine to A site 3) Peptide bond forms in P site 4) tRNA exits E site 5) Ribosome moves down mRNA 6) Repeats until stop codon 7) Release factor binds stop codon 8) Ribosome releases protein

Ribosome Sites E, P, A

A site = Aminoacyl-tRNA enters with new amino acid. P site = Peptide (growing protein chain). E site = Exit site where used tRNA leaves.

tRNA Structure

A looped RNA molecule. One end has an anticodon (complementary to the mRNA codon). The other end carries the specific amino acid.

Anticodon

The three-base sequence on tRNA that is complementary to the mRNA codon. Ensures the correct amino acid is brought to the ribosome.

Peptide Bond

The bond formed between amino acids during translation. Forms through a dehydration reaction between the carboxyl group of one and the amino group of the next.

Primary Protein Structure

The linear sequence of amino acids that makes up a protein. Determined by the mRNA sequence.

Release Factor

A protein that binds to the stop codon in the ribosome. Triggers the ribosome to fall apart and release the completed polypeptide chain.

Posttranslational Modification

Changes made to a protein after translation is complete — side chains may be modified or altered so the protein can do its specific job.

Using a Codon Table

Split mRNA into triplets starting from AUG. Find first base on left column, second base on top, third base on right. The intersection gives the amino acid.

Why RNA is Unique for Life's Origin

RNA can BOTH store genetic information (like DNA) AND catalyze reactions (like protein enzymes). No other molecule can do both.

Evidence for RNA World - Ribozymes

In 1982, ribozymes (RNA molecules that catalyze reactions) were discovered. Before this, only proteins were thought to catalyze reactions.

Evidence for RNA World - Ribosome

The ribosome — the machine that makes all proteins — is itself largely made of RNA (rRNA), suggesting it is a relic of an RNA-based world.

Evidence for RNA World - Coenzymes

Many coenzymes contain RNA-like sections, suggesting they are evolutionary remnants of an earlier RNA-based biochemical world.

Evidence for RNA World - Lab Experiments

Scientists have created self-replicating (autocatalytic) ribozymes in the lab and shown tRNA can be modified to replicate autonomously — demonstrating the chemistry is possible.

Why Mistakes in Replication Make Evolution Possible

Perfect copying = no variation = no evolution. Replication errors create mutations. Most are harmful or neutral, but occasionally one helps. Those organisms reproduce more, passing the advantage on — this is how populations change over time.

Natural Selection

The non-random mechanism of evolution. Individuals with heritable traits that help them survive and reproduce better leave more offspring. Over generations, those traits become more common in the population. This produces adaptations.

Biological Fitness

An organism's ability to survive and reproduce relative to others in the population. NOT about physical strength — just about leaving more offspring.

Genetic Drift

The random mechanism of evolution. Allele frequencies change between generations due to chance alone — like getting 7 heads in 10 coin flips. More impactful in small populations. Does NOT necessarily produce adaptive change.

Why Heredity is Necessary for Evolution

Without heredity, neither natural selection nor genetic drift can change a population over time. Traits must be passed from parent to offspring for any evolutionary change to accumulate across generations.

Adaptations as Emergent Features of Populations

No individual organism evolves — individuals are born with fixed genomes. It is the POPULATION that changes over time as better-adapted alleles become more common. Adaptations emerge from heritable variation + differential reproduction, repeated over many generations.

Evolution Definition

Descent with modification. The change in heritable characteristics of a population over time. Driven by natural selection and genetic drift.

RNA World Implication for Natural Selection

If RNA replicators came first — before cells, before metabolism — then natural selection was already operating BEFORE life truly began. The algorithm predates living organisms; life was built around it.

Prokaryote vs Eukaryote Transcription/Translation Location

In prokaryotes, both transcription and translation occur in the cytoplasm (no nucleus). In eukaryotes, transcription is in the nucleus and translation is in the cytoplasm.

Non-coding DNA

DNA that does not code for proteins. Humans have a lot of it — in E. coli there is 1 gene per 1,400 bases; in humans only 1 gene per 100,000 bases.

Avery-MacLeod-McCarty Experiment

The experiment that proved DNA (not protein) carries genetic information. Watson and Crick did NOT do this.

Rosalind Franklin

The scientist who actually took Photo 51 (X-ray diffraction image of DNA) and correctly identified its significance. Watson and Crick used her data without her knowledge and received the Nobel Prize she never got.