w3 slides fc Flashcards

Question

How are eukaryotic chromosomes organized within the nucleus? (A) Chromosomes occupy distinct territories to prevent tangling (B) They float randomly throughout the nucleoplasm (C) They interact with the endoplasmic reticulum (D) They move freely between the cytoplasm and nucleus

Answer 1

Answer: (A) (Chromosome territories help organize nuclear function.)

Answer 2

Answer: (A) (Nuclear pores control movement of molecules between the nucleus and cytoplasm.)

Answer 3

-histones are small proteins- rich in lysine and arginine -positive charge neutralizes negative charge of DNA (wrapping DNA around histone helps with neutralization)

Answer 4

Structure: H1 is not part of the histone octamer but is a separate histone protein. It has a globular central domain and long N- and C-terminal tails, which interact with DNA. Function: Stabilizes nucleosome structure by binding where DNA enters and exits the nucleosome core. Compacts chromatin by promoting the formation of higher-order chromatin structures (30-nm fiber). Regulates gene expression by influencing DNA accessibility to transcription factors and polymerases. Key Concept: H1 acts as a "clamp" to secure DNA around nucleosomes and facilitates chromatin compaction.

Answer 5

-sequence-specific clamp proteins and cohesins are involved in forming chromatin loops -as cells enter mitosis, condensins replace most cohesins to form double loops of chromatin to generate compact chromosomes

Answer 6

Structure: Cohesins are ring-shaped protein complexes composed of SMC (Structural Maintenance of Chromosomes) proteins and accessory subunits. The core complex includes SMC1, SMC3, SCC1 (RAD21), and SCC3. Function: Chromatid Cohesion: Holds sister chromatids together from S-phase until anaphase to ensure accurate chromosome segregation. DNA Repair: Helps facilitate homologous recombination by keeping sister chromatids close. Gene Regulation & Chromatin Structure: Contributes to chromatin looping, regulating transcription. Separation During Anaphase: Cleaved by separase enzyme, allowing sister chromatids to separate during mitosis/meiosis. Key Concept: Cohesins act as molecular "glue" holding sister chromatids together until they are properly aligned for separation.

Answer 7

Highly condensed chromatin -meiotic and mitotic chromosomes -centromeres and telomeres -time spent highly condensed varies -heterochromatic regions of interphase chromosomes are areas where gene expression is SURPRESSED

Answer 8

relatively non-condensed chromatin -degree of condensation varies -level of activity varies active euchromatic regions of interphase chromosomes are areas where genes tend to be expressed

Answer 9

Structure: Condensins are multi-subunit protein complexes belonging to the SMC (Structural Maintenance of Chromosomes) family. Core subunits include SMC2 and SMC4, along with regulatory subunits (CAP-D2, CAP-G, CAP-H in condensin I; CAP-D3, CAP-G2, CAP-H2 in condensin II). Function: Chromosome Condensation: Compacts DNA during mitosis and meiosis, facilitating chromosome segregation. Loop Extrusion: Helps create and stabilize chromatin loops, essential for higher-order chromosome structure. Regulation of Gene Expression: Influences chromatin architecture, impacting transcriptional activity. Chromosome Segregation: Ensures proper chromosome alignment and prevents tangling during cell division. Key Concept: Condensins drive chromosome compaction, ensuring proper segregation during mitosis and meiosis by organizing DNA into higher-order structures.

Answer 10

gene OFF: genes in the middle of compact chromatin, homologous chromosomes detected by hybridization techniques gene ON: genes move around from condensed(compact) area

Answer 11

there are 3 main models but focusing on... Bidirectional growth from one starting point in the 5' to 3' direction

Answer 12

Always starts from the same location on DNA -What are some of the characteristics of the sequences at replication origins? --easy to open, A-T rich --recognized by initiator proteins that bind to the DNA

Answer 13

this style of replication only applies to: -circular genomes

Answer 14

Replication fork is ASYMMETRICAL -strands get duplicated differently Leading strand replicated continuously -lagging strand replicated discontinuously

Answer 15

1) separate DNA strands 2) synthesize DNA 3) proofread newly synthesized dna

Answer 16

origin of replication primers dNTPs (building blocks for dna) ATP (energy source) DNA polymerase Accessory proteins

Answer 17

Chromatin = DNA + Proteins (like a coiled telephone wire) 🟢 Euchromatin → Loose, active, genes ON 🟢 🔴 Heterochromatin → Tightly packed, genes OFF 🔴 🚨 Exam Tip: Heterochromatin is found at centromeres & telomeres (stays permanently off).

Answer 18

Imagine unzipping a zipper. That’s what helicase does! 🔹 Leading strand – Copied continuously 🔹 Lagging strand – Copied in fragments (Okazaki fragments) 💡 Key Concept: DNA polymerase can’t start on its own – it needs an RNA primer! 🚨 Exam Tip: Primase makes RNA primers to help start DNA replication.

Answer 19

🚀 Helicase → Unzips DNA (breaks hydrogen bonds) 🧷 Single-Strand Binding Proteins (SSBs) → Keep strands apart 🔗 Primase → Lays down RNA primer 🛠 DNA Polymerase → Adds new DNA (5’ → 3’ only!) ✂️ DNA Ligase → Seals Okazaki fragments

Answer 20

1️⃣ Origin of Replication (oriC) – The starting point where replication begins. 2️⃣ Binding of Initiator Proteins – These proteins recognize oriC and prepare DNA for copying. 3️⃣ Unwinding by Helicase – The "unzipping" enzyme breaks hydrogen bonds between bases. 4️⃣ Single-Strand Binding Proteins (SSBs) – These keep the strands apart so they don’t reattach. 5️⃣ RNA Primers Made by Primase – DNA polymerase needs a starting point, so primase lays down short RNA primers. 6️⃣ DNA Polymerase – The builder enzyme adds new DNA nucleotides in the 5' → 3' direction. 7️⃣ Sliding Clamp – Holds DNA polymerase in place so it doesn’t fall off the DNA strand. 8️⃣ Nick Sealing by DNA Ligase – DNA ligase glues Okazaki fragments together on the lagging strand

Answer 21

✅ DNA replication is semi-conservative (1 old + 1 new strand). ✅ Helicase unwinds DNA; SSBs keep strands apart; DNA polymerase builds new DNA. ✅ Leading strand = continuous; lagging strand = Okazaki fragments. ✅ Telomerase prevents chromosome shortening. ✅ DNA polymerase has proofreading (3’ → 5’ exonuclease activity). ✅ Mismatch repair corrects replication errors that proofreading misses. ✅ NER removes bulky DNA damage like thymine dimers.

Answer 22

📌 RNA polymerase must find the right place to start transcribing DNA into RNA. This start point is called the promoter. 🛠 Key Players in Bacterial Transcription Initiation: ✅ RNA Polymerase → The enzyme that builds RNA ✅ Sigma Factor (σ factor) → Helps RNA polymerase find the promoter ✅ Promoter Sequences (-10 and -35 regions) → Specific DNA sequences that signal RNA polymerase where to bind 💡 Easy Analogy: RNA polymerase is like a car, and the sigma factor is like GPS guiding it to the correct starting location (promoter).

Answer 23

Once RNA polymerase starts, sigma factor leaves and RNA polymerase moves forward, adding RNA nucleotides. 📌 Key Points: ✅ RNA is made 5’ → 3’ (just like DNA replication!) ✅ RNA polymerase does not need a primer ✅ The RNA strand is complementary to the DNA template strand 💡 Easy Analogy: Think of RNA polymerase like a train, and DNA is the track. The train moves forward, laying down new RNA “tracks” behind it. 🚨 Exam Tip: RNA polymerase does NOT proofread like DNA polymerase!

Answer 24

1️⃣ Silent Mutation – No change in the amino acid (due to redundancy) 2️⃣ Missense Mutation – One amino acid is changed (can be harmless or harmful) 3️⃣ Nonsense Mutation – Creates a STOP codon → Protein is too short! 4️⃣ Frameshift Mutation – Insertion/deletion shifts the reading frame → Disastrous!