BIS 10 module 1/2 review

A study finds that people who eat more leafy greens have lower rates of heart disease. Which conclusion is best supported by this finding alone?

Leafy green consumption is statistically associated with lower heart disease rates; causation has not been established.

A double-stranded DNA sample is found to contain 18% adenine. What percentage of the sample is cytosine?

32%

A point mutation changes a codon from UAC (tyrosine) to UAA. The most likely consequence is:

The protein is truncated (UAA is a stop codon).

Why does seasonal influenza require a new vaccine almost every year?

Influenza accumulates small mutations in surface proteins (antigenic drift), so last year’s vaccine no longer matches as well.

Why don’t mRNA vaccines permanently change your DNA?

mRNA is translated in the cytoplasm and degrades quickly; it never enters the nucleus where DNA is stored.

Hypothesis

A tentative, testable explanation for an observation. Always falsifiable in principle

Theory (scientific)

A broad, well-substantiated explanation supported by many independent lines of evidence.

Falsifiability

The property that a claim can in principle be shown false by some test.

Required for scientific claims.

Correlation

A statistical association between two variables. Does not by itself establish causation.

Inductive reasoning

Going from specific observations to a general hypothesis. Generates hypotheses but cannot prove them.

Deductive reasoning

Going from a general rule to a specific prediction. Allows hypotheses to be tested and falsified.

Covalent bond

A strong chemical bond formed by sharing electrons.

Ionic bond

A bond formed by electrostatic attraction between oppositely charged ions.

Hydrogen bond

A weak attraction between a hydrogen covalently bonded to an

electronegative atom and another electronegative atom. Critical for water, DNA, and proteins.

Hydrophilic

"Water-loving": polar or charged, interacts favorably with water

Hydrophobic

"Water-fearing": nonpolar, does not interact favorably with water.

Hydrophobic effect

The exclusion of nonpolar molecules from water, driving phenomena like membrane self-assembly.

Homology

Similarity in structure or sequence due to descent from a common ancestor.

Analogy

Similar form or function arising independently, not from common ancestry.

Chargaff’s rule

In double-stranded DNA, the amount of A equals the amount of T, and G equals C.

Antiparallel

The two strands of DNA run in opposite directions (5′→3′ on one strand, 3′→5′ on the other).

Complementary base pairing

A pairs with T (or U in RNA), G pairs with C.

Virus

An infectious particle made of a genome (DNA or RNA) inside a protein

capsid (sometimes with a lipid envelope). Cannot reproduce without a host cell

Capsid

The protein coat surrounding a viral genome.

Envelope

The lipid membrane some viruses have, acquired from a host cell membrane.

Retrovirus

A virus that uses reverse transcriptase to copy its RNA genome into

DNA, which then integrates into the host genome. HIV is the example.

Reverse transcriptase

The viral enzyme that copies RNA into DNA.

Lytic cycle

Viral life cycle where the virus immediately replicates and destroys the host cell.

Lysogenic cycle

Viral life cycle where the viral genome integrates into the host genome and can remain dormant.

Antigenic drift

Small mutations in viral surface proteins (reason flu vaccines change yearly).

Antigenic shift

Large changes from swapping whole genome segments (source of pandemic flu strains).

Central dogma

DNA → RNA → protein. The flow of genetic information.

Replication

Copying DNA to make a second identical molecule. Semiconservative.

Transcription

Making an mRNA copy of a gene. Performed by RNA polymerase.

Happens in the nucleus in eukaryotes.

Translation

Making a protein from an mRNA. Performed by the ribosome. Happens in the cytoplasm

mRNA

Messenger RNA. The working copy of a gene.

tRNA

Transfer RNA. Carries an amino acid and recognizes the matching codon on the mRNA via its anticodon.

Codon

A three-base sequence on the mRNA that specifies one amino acid (or

a stop signal).

Anticodon

The three-base sequence on a tRNA that base-pairs with the codon

Start codon

AUG — codes for methionine and signals the start of translation.

Stop codon

UAA, UAG, or UGA; signals the end of translation.

Splicing

The removal of introns and joining of exons during eukaryotic pre-mRNA processing.

Mutation

A change in the DNA sequence of a cell.

Silent mutation

A base change that does not change the amino acid (because the code is redundant).

Missense mutation

A base change that changes one amino acid to a different one.

Nonsense mutation

A base change that creates a stop codon, truncating the protein.

Frameshift mutation

An insertion or deletion of bases (not divisible by 3) that shifts the reading frame.

CRISPR-Cas9

A bacterial defense system against viruses, now used as a gene-editing

tool.

Viral vector

A modified, harmless virus used to deliver therapeutic genes in gene

therapy.

mRNA vaccine

A vaccine that delivers mRNA instructing your cells to temporarily make

a viral protein. The mRNA does not enter the nucleus or change DNA.