Ch 7-8

What is the central dogma of molecular biology?

DNA → RNA → Protein

How is RNA different from DNA?

Single-stranded, ribose sugar, uracil instead of thymine

What is transcription?

The process of making RNA from a DNA template

What is translation?

The process of using mRNA to build a protein

What does mRNA do?

Carries the genetic code (codons) from DNA

What does tRNA do?

Brings amino acids to the ribosome using anticodons

What does rRNA do?

Forms the ribosome, where proteins are made

Where does transcription occur?

Nucleus in eukaryotes; cytoplasm in prokaryotes

Where does translation occur?

Cytoplasm (in both eukaryotes and prokaryotes)

What is a codon?

3-base sequence in mRNA that codes for an amino acid

What is an anticodon?

3-base sequence in tRNA that pairs with codons

What is the start codon?

AUG

Why is the genetic code called redundant?

Multiple codons can code for the same amino acid

Why is the genetic code unambiguous?

Each codon only codes for one specific amino acid

What are the 3 steps of transcription?

Initiation, Elongation, Termination

What enzyme starts transcription?

RNA polymerase

What happens during transcription initiation?

RNA polymerase binds to the promoter on DNA

In what direction is RNA made?

5’ to 3’ direction

What are the RNA base-pairing rules?

A–U, T–A, C–G, G–C

What happens at transcription termination?

RNA polymerase reaches a stop signal and releases RNA

What is RNA splicing?

Introns are removed; exons are joined together

What is added to mRNA before it leaves the nucleus?

5’ cap and 3’ poly-A tail

What are the 3 steps of translation?

Initiation, Elongation, Termination

What starts translation?

Small ribosomal subunit binds to mRNA, then tRNA binds to start codon

What links amino acids during elongation?

Peptide bonds catalyzed by rRNA

What happens during translation termination?

Stop codon is reached, and the protein is released

What helps proteins fold correctly?

Chaperone proteins

What is an operon?

A group of genes regulated together in prokaryotes

What does the Lac Operon do?

Breaks down lactose using dual (positive and negative) control

What does the Trp Operon do?

Makes tryptophan using negative control

How is gene expression regulated in eukaryotes?

At transcription, splicing, mRNA degradation, and protein folding

What is a mutation?

A change in the DNA sequence

What causes mutations?

Errors during DNA replication that aren’t corrected

What are the effects of mutations?

Silent, beneficial, or harmful; may pass to offspring

Why are mutations important to evolution?

They introduce variation that natural selection can act on

What are the two types of cell division?

Mitosis and Meiosis

What is the purpose of mitosis?

Growth, repair, and asexual reproduction (produces identical cells)

What is the purpose of meiosis?

Creates gametes (sperm/egg) for sexual reproduction

What are somatic cells?

Body cells that divide by mitosis

What are gametes?

Sex cells (sperm and egg), made by meiosis

How many chromosomes do humans have in somatic cells?

46 chromosomes (23 pairs)

How many chromosomes do gametes have?

23 chromosomes (haploid)

What are sister chromatids?

Identical copies of a chromosome joined at the centromere

What is a centromere?

Region where sister chromatids are attached

What happens in the cell cycle?

Interphase (G1, S, G2) + M phase (Mitosis + Cytokinesis)

What happens during interphase?

Cell grows, DNA replicates, prepares to divide

What happens in G1 phase?

Cell growth and normal functions

What happens in S phase?

DNA is replicated

What happens in G2 phase?

Cell prepares for mitosis; organelles replicate

What are the 4 stages of mitosis?

Prophase, Metaphase, Anaphase, Telophase

What happens in prophase?

Chromosomes condense, spindle forms, nuclear envelope breaks down

What happens in metaphase?

Chromosomes align at the center (metaphase plate)

What happens in anaphase?

Sister chromatids separate and move to opposite poles

What happens in telophase?

Nuclear membranes reform, chromosomes uncoil

What is cytokinesis?

Division of the cytoplasm into two cells

What are checkpoints in the cell cycle?

Control points that regulate cell division

What is the G1 checkpoint?

Checks for size, nutrients, and DNA damage

What happens if a cell doesn’t pass the G1 checkpoint?

It enters G0 (resting state or permanent exit)

What is cancer?

Uncontrolled cell division

What causes cancer?

Mutations in genes that control the cell cycle

What are oncogenes?

Mutated genes that promote cell division (can lead to cancer)

What are tumor suppressor genes?

Genes that stop cell division; when mutated, cancer can develop

What is apoptosis?

Programmed cell death

What is meiosis?

A two-part division that reduces chromosome number by half

How many cells are made by meiosis?

4 non-identical haploid cells

What happens in meiosis I?

Homologous chromosomes separate

What happens in meiosis II?

Sister chromatids separate

What is crossing over?

Exchange of genetic material between homologous chromosomes during Prophase I

What is independent assortment?

Random distribution of chromosomes during meiosis

Why is meiosis important?

Increases genetic variation in offspring