Comprehensive Genetics and Molecular Biology Review for Final Exam

What is a gene?

A segment of DNA that has the information for a protein or RNA.

What is the central dogma of molecular biology?

DNA → RNA → Protein (Transcription then Translation)

What are the 4 DNA bases?

Adenine (A), Thymine (T), Guanine (G), and Cytosine (C)

How many hydrogen bonds between A-T and G-C?

A-T has 2 hydrogen bonds, G-C has 3 hydrogen bonds.

What is the sugar in DNA?

Deoxyribose

What gives DNA its 5' to 3' polarity?

Phosphodiester bonds form between the 3' carbon of one nucleotide and the 5' carbon of the next nucleotide.

If Mike VII's genome is 30% Adenine, what percent is Cytosine?

20% C and 20% G.

What direction does DNA synthesis occur?

5' to 3' direction only.

What enzyme adds complementary bases during DNA replication?

DNA Polymerase

What is a replication fork?

Localized region of unpairing between parental strands where replication actively occurs.

What is the leading strand?

The daughter strand synthesized continuously in the 5'→3' direction.

What is the lagging strand?

The daughter strand synthesized discontinuously in the 5'→3' direction via Okazaki fragments.

What are Okazaki fragments?

Transient pieces of DNA on the lagging strand that must be joined together.

What enzyme joins Okazaki fragments?

DNA ligase

What does DNA primase do?

Produces a base-paired RNA primer that DNA polymerase uses to polymerize strands.

What opens up the DNA at the replication fork?

DNA helicase (uses ATP hydrolysis).

What is a replication origin?

Position where the DNA helix is first opened for replication.

What are telomeres?

Repetitive DNA sequences at the ends of chromosomes that protect against shortening during division.

What enzyme extends telomeres?

Telomerase.

DNA replication is ___________

Semiconservative.

What does DNA polymerase require to add nucleotides?

A primer.

What are the 5 key features of DNA polymerases?

1. Need a template; 2. Directional - add only to 3' end; 3. Cannot start from scratch - need primer; 4. Proofread and remove wrong nucleotides; 5. Get energy from phosphate bonds in dNTPs.

What is a replication bubble?

Structure formed when replication is active on both strands of parental DNA double helix.

What enzyme relaxes supercoils ahead of the replication fork?

Topoisomerase.

What does DNA polymerase I do?

Replaces RNA primer with DNA sequence.

What are the major tasks of the cell cycle?

1. Replicate the genome; 2. Segregate copies; 3. Divide the cell.

What happens in S phase?

DNA synthesis - chromosomes replicate to form sister chromatids.

What is the longest phase of the cell cycle?

Interphase.

What are the phases of interphase?

G1, S, and G2.

What is G0 phase?

A prolonged, non-dividing state.

What are the 3 cell cycle checkpoints?

1. Late G1; 2. G2/M transition; 3. Metaphase-to-anaphase.

What are cyclins and CDKs?

CDKs are constant levels; cyclins vary by cell cycle stage.

What are the 5 stages of mitosis?

Prophase, Prometaphase, Metaphase, Anaphase, Telophase.

What happens in prophase?

Chromosomes condense and become visible.

What happens in prometaphase?

Spindle forms, nuclear envelope breaks down.

What happens in metaphase?

Chromosomes align at the cell equator.

What happens in anaphase?

Sister chromatids separate and move to opposite poles.

What happens in telophase?

Chromosomes decondense, spindle disassembles.

What happens in cytokinesis?

Cytoplasm divides by a contractile actomyosin ring.

Sister chromatids are ____________

Identical copies of a chromosome.

How many sister chromatids are there in a person with 46 chromosomes?

92 sister chromatids.

Two sister chromatids connected together = _____ chromosome(s)

1 chromosome.

What is the goal of meiosis?

Generate haploid gametes.

How many rounds of division in meiosis?

Two rounds.

What happens in meiosis I?

Homologs pair, cross over, and segregate.

What happens in meiosis II?

Sister chromatids separate.

What is crossing over/recombination?

Maternal and paternal homologs exchange genetic material.

What is nondisjunction?

Mistakes in chromosome segregation.

What is a gamete?

Sex cells = sperm or egg.

What is a zygote?

A fertilized egg.

What is the difference between somatic and germ cells?

Somatic cells make up most of the body; germ cells are precursors to gametes.

Homologous chromosomes: one from _____ parent, one from _____ parent

One from male parent, one from female parent.

What are the first 22 pairs of homologous chromosomes called?

Autosomes.

What are the sex chromosomes for females and males?

Female = XX; Male = XY.

What is the difference between sister chromatids and homologs?

Sister chromatids are identical; homologs can have different alleles.

Which mutation rate is higher: sperm or eggs?

Sperm.

What are histones?

Proteins associated with DNA that help DNA coil up.

What are non-histone proteins?

Proteins that regulate turning genes on and off.

When are chromosomes visible?

Only when a cell is dividing.

Diploid (2n) means:

Two sets of chromosomes.

Haploid (n) means:

One set of chromosomes.

What is a chromatid?

One of two exact copies of a chromosome.

What is the centromere?

The point where sister chromatids are connected.

What is a mutation?

A permanent change to DNA sequence.

What is a silent mutation?

No change in the coded amino acid.

What is a nonsense mutation?

Produces an early stop codon.

What is a missense mutation?

Codes for a different amino acid.

What is a frameshift mutation?

Insertion or deletion that alters all downstream amino acids.

What is a somatic mutation?

Occurs in non-germ cells; not transmitted to offspring.

What is a germline mutation?

Occurs in gametes; transmitted to next generation.

What are 3 ways DNA can be damaged?

1. Damage to nucleotide bases; 2. Crosslinks; 3. Breaks.

What causes thymidine dimers?

UV light (UVB) - causes abnormal bonds between adjacent pyrimidines

What is an abasic site?

A base is missing (hydrolytic depurination - most common DNA damage)

What is 8-oxo-dG?

Oxidized guanine that can pair with A instead of C (Hoogsteen base pairing)

What is Xeroderma Pigmentosum?

Inability to repair large lesions and pyrimidine dimers (thymidine dimers), leading to increased skin cancer

What is Lynch Syndrome?

Hereditary nonpolyposis colorectal cancer; autosomal dominant defect in mismatch repair; 60-80% lifetime risk of CRC

What are the two types of double-strand break repair?

Homologous Recombination Repair (HRR) - more accurate; Non-homologous End Joining (NHEJ) - more error-prone

What is the role of ATM and ATR?

Kinases that sense DNA damage; ATM for G1-S, ATR for I-S and G2-M checkpoints

What does p53 do?

Activated by phosphorylation; can halt cell cycle, activate DNA repair, or trigger apoptosis

What are the 3 major chemical differences between RNA and DNA?

1. Ribose instead of deoxyribose; 2. Uracil instead of Thymine; 3. Most RNA is single-stranded

What is a codon?

3 bases in mRNA that code for 1 amino acid

What are the 3 stop codons?

UAA, UAG, UGA

What is the start codon?

AUG (codes for Methionine)

What is the role of tRNA?

Carries amino acids and has an anticodon complementary to the mRNA codon

What is the wobble base?

The third base position that allows some tRNAs to recognize more than one codon (explains genetic code degeneracy)

What is alternative splicing?

Different mRNAs can be produced from the same primary transcript by splicing out different introns

What are introns and exons?

Introns are non-coding regions removed during splicing; exons are coding regions kept in mature mRNA

What percent of the human genome codes for proteins?

Only about 2%.

What is an allele?

Alternative forms of a single gene

What is Mendel's Law of Segregation?

Two alleles for each trait separate during gamete formation; each gamete gets only one allele

What is Mendel's Law of Independent Assortment?

Genes for different traits segregate independently during gamete formation

What is Mendel's Law of Dominance?

The phenotype of a recessive allele is always masked by the dominant allele

What is the F2 phenotypic ratio from a monohybrid cross (Aa × Aa)?

3:1 (3 dominant phenotype : 1 recessive phenotype)

What is the F2 genotypic ratio from a monohybrid cross (Aa × Aa)?

1:2:1 (1 AA : 2 Aa : 1 aa)

What is the phenotypic ratio from a testcross (Aa × aa)?

1:1 (1 Aa : 1 aa)

What is the F2 phenotypic ratio from a dihybrid cross (AaBb × AaBb)?

9:3:3:1

What does a 2:1 ratio in offspring indicate?

A recessive lethal allele (e.g., AY allele in yellow mice - AYAY not viable)

What is a genotype?

The pair of alleles in an individual (e.g., YY or Yy)

What is a phenotype?

Observable characteristic (e.g., yellow or green peas)

Homozygote vs. Heterozygote?

Homozygote = two identical alleles (YY or yy); Heterozygote = two different alleles (Yy)