exam 3 bio

Components of a DNA nucleotide

Phosphate group, deoxyribose sugar, nitrogen base (A, T, C, G).

Base pairing rules (Chargaff’s rules)

A pairs with T: G pairs with C.

Rosalind Franklin discovery

X-ray diffraction showed DNA is a helix.

Why DNA replication is semiconservative

Each new DNA molecule has one old strand and one new strand.

Helicase

Enzyme that unwinds DNA during replication.

DNA polymerase

Adds new nucleotides during DNA replication.

DNA ligase

Seals breaks in DNA backbone; joins Okazaki fragments.

RNA differences from DNA

RNA has ribose, uracil, and is single-stranded.

Three types of RNA

mRNA, tRNA, rRNA.

mRNA function

Carries genetic information from DNA to ribosomes.

tRNA function

Brings amino acids to the ribosome using its anticodon.

rRNA function

Structural and functional component of ribosomes.

Transcription

Formation of mRNA from a DNA template by RNA polymerase.

Codon

Three-base sequence on mRNA that codes for an amino acid.

Anticodon

Three-base sequence on tRNA that pairs with an mRNA codon.

Three stages of translation

Initiation, elongation, termination.

G1 checkpoint

Ensures cell is ready to divide, failure sends cell to G0.

G2 checkpoint

Ensures DNA replication was completed correctly before mitosis

Proto-oncogene

Normal gene that promotes cell cycle and prevents apoptosis.

Oncogene

Mutated proto-oncogene causing uncontrolled cell division.

Tumor suppressor gene

Gene that inhibits cell cycle and promotes apoptosis.

p16 mutation

Causes continuous cyclin activation → uncontrolled division.

Telomerase in cancer

Rebuilds telomeres, making cancer cells effectively “immortal.”

Angiogenesis

Formation of new blood vessels that feed tumors.

Purpose of mitosis

Growth, repair, and production of genetically identical cells.

Interphase G1

Cell grows and organelles duplicate.

Interphase S

DNA replication, sister chromatids form.

Interphase G2

Cell produces proteins needed for division.

Prophase

Chromosomes condense, spindle forms; nuclear envelope breaks down.

Metaphase

Chromosomes align at the cell equator.

Anaphase

Sister chromatids separate to opposite poles.

Telophase

Nuclear envelopes reform; chromosomes uncoil.

Cytokinesis

Division of the cytoplasm into two daughter cells.

Cleavage furrow

Indentation used for animal cell cytokinesis.

Cell plate

New wall forming between plant daughter cells during cytokinesis.

Purpose of meiosis

Produces haploid gametes for sexual reproduction.

Homologous chromosomes

Chromosome pairs with same genes but possibly different alleles.

Haploid number (n)

Number of chromosomes in gametes.

Diploid number (2n)

Full chromosome set in body cells.

Synapsis

Homologous chromosomes pair in prophase I.

Tetrad

Structure of four chromatids during synapsis.

Crossing-over

Exchange of genetic material between nonsister chromatids.

Result of crossing-over

Produces new allele combinations and increases variation.

When cell becomes haploid

Anaphase I when homologous chromosomes separate.

Meiosis I

Homologous chromosomes separate.

Meiosis II

Sister chromatids separate, producing four haploid cells.

Meiosis vs mitosis (chromosomes)

Meiosis halves chromosome number, mitosis keeps it the same.

Meiosis vs mitosis (genetics)

Meiosis creates diverse cells, mitosis creates identical cells.

Law of Segregation

Alleles separate during gamete formation.

Law of Independent Assortment

Allele pairs assort independently during meiosis.

Genotype

Genetic makeup (BB, Bb, bb).

Phenotype

Physical expression of a trait.

Homozygous

Two identical alleles.

Heterozygous

Two different alleles.

Testcross

Cross with homozygous recessive to determine unknown genotype.

Incomplete dominance

Heterozygote shows intermediate phenotype.

Polygenic inheritance

Trait controlled by multiple genes.

X-linked trait

Trait controlled by genes on the X chromosome.

Carrier (X-linked)

Female with one recessive allele who does not express the trait.