Unit 1 review Flashcards

Question

Describe the role of the spliceosome.

Answer 1

Splice out introns

Answer 2

Differential Processing: the process where a single gene can produce multiple different protein variants by selectively splicing its mRNA transcript

Answer 3

- Shine del garno sequence- positions ribosome relative to start codon - Start codon - Initiator tRNA carries fMet

Answer 4

peptide bond: carbonyl group and amino group undergo dehydration reaction

Answer 5

A (Aminoacetyl site): where new amino acid, carrying tRNA enters ACCEPTS NEW AMINO ACID P(Peptidyl site): holds tRNA with growing polypeptide chain BUILDS POLYPEPTIDE CHAIN E(exit site): where tRNA exits after releasing its amino acid RELEASES SPENT TRNA

Answer 6

DRAW 1. IF3 binds SSU 2. GTP + IF1 (goes to SSU)+ IF2 (works with GTP and tRNA) + tRNA charged with fMet 3. IF1, IF2, IF3, GDP, Pi, released LSU binds

Answer 7

Release factor: terminates translation by recognizing stop codons and telling the ribosome to release the newly formed polypeptide

Answer 8

Positive Supercoiling- molecules that are overrotated- hinders transcription by making DNA less accessible Negative Supercoiling- molecules that are under rotated- activate transcription by making DNA more accessible

Answer 9

Conserved sequences (stayed the same) — likely essential for survival. Divergent sequences (changed over time) — suggest adaptations or evolutionary changes. For example, comparing human and chimpanzee genomes shows how closely related we are and highlights specific changes that led to differences.

Answer 10

Chromatin: the material from which the chromosomes of an organism are composed of- a complex made of DNA and proteins (histones are most abundant) Heterochromatin: highly condensed, characterized by a lack of transcription Euchromatin: un-condensed form (loose), where most transcription takes place

Answer 11

“Open” chromatin refers to a relaxed, less compacted state of chromatin where DNA is more accessible to proteins like transcription factors, RNA polymerase, and other regulatory machinery. Detected Experimentally: DNA Methylation Analysis - Which genes are turned on or off in different cell types or conditions. - Epigenetic differences between healthy and diseased tissue (e.g., cancer). - How development, aging, or environmental exposures affect gene regulation.

Answer 12

DNA tends to wrap tightly around nucleosomes due to the large positive charge of histones. This tendency ca be relaxed through 1. histone acetylation (neutralizes the negative charge of DNA) 2. Chromatin remodeling complex (slides nucleosomes to promote gene expression 3. Histone methylation (activates chromatin transcription)

Answer 13

They act like "caps," preventing the ends of chromosomes from being recognized as broken DNA by DNA repair systems. This prevents them from being mistakenly joined together or undergoing degradation. Telomeres allow for the complete replication of chromosome ends, which would otherwise be lost during the replication process. This is facilitated by the enzyme telomerase, which adds repetitive DNA sequences to the telomere ends, maintaining their length.

Answer 14

Pedigrees are used in diagnosing genetic disorders to track the inheritance of traits and identify patterns that suggest whether a condition is genetic and how it is passed down through families.

Answer 15

Semi-conservative replication: the mode by which DNA replicates- each strand acts as a template for a new double helix

Answer 16

The Meselson-Stahl experiment (1958) was a landmark study that demonstrated DNA replicates semi-conservatively—meaning each daughter DNA molecule consists of one old (parental) strand and one new strand. Experiment: Labeling DNA with Heavy Nitrogen (¹⁵N): E. coli were grown in ¹⁵N (heavy nitrogen) medium so their DNA was "heavy". Switching to Light Nitrogen (¹⁴N): Cells were then moved to ¹⁴N (light nitrogen) medium and allowed to replicate. DNA Density Separation: DNA was extracted after each round of replication and separated by density-gradient centrifugation (heavier DNA migrates lower in the gradient). Meselson-Stahl's data strongly supported the semi-conservative model of DNA replication. Each new DNA molecule keeps one old strand and synthesizes one new strand. The conservative model was ruled out by the absence of a heavy band after one generation.

Answer 17

1. DNA polymerase can only synthesize DNA in the 5′ → 3′ direction. This means it adds nucleotides to the 3′ end of the growing DNA strand. 2. DNA polymerase cannot start synthesis from scratch. It requires a pre-existing short strand of nucleotides (called a primer) with a free 3′ OH group to add new nucleotides to. 3. DNA polymerase needs a single-stranded DNA template to read and copy. The enzyme uses this strand to determine which complementary nucleotide to add next.

Answer 18

1. RNA primer removal by DNA Pol I- leaves a gap 2. Gap filling by DNA Pol I- adds nucleotides to fill gap 3. Sealing the Gap by DNA ligase by reforming the phosphodiester bond

Answer 19

1. Epigenetic Modifications - DNA Methylation - Histone modifications 2. Gene Expression Regulation Different cells express different sets of genes due to the presence or absence of specific transcription factors or regulatory molecules that bind to DNA and activate or repress gene transcription. 3. Alternative Splicing Alternative splicing of mRNA transcripts allows a single gene to give rise to multiple protein isoforms. 4. Environmental Influence The environment can affect gene expression and the resulting phenotype, even in cells with identical genetic material. For example, changes in temperature

Answer 20

Eukaryotes Promoter: DNA sequence where RNA polymerase binds to begin transcription Transcription Start Site (TSS): The first nucleotide transcribed into RNA 5′ UTR (Untranslated Region): Transcribed but not translated; important for regulation Coding Sequence (CDS): Region that is translated into protein Introns (eukaryotes only): Non-coding regions removed from mRNA during splicing Exons (eukaryotes only): Coding sequences that remain in mature mRNA 3′ UTR: Transcribed but not translated; includes regulatory elements Transcription Terminator: Signals RNA polymerase to stop transcription Enhancers/Silencers (eukaryotes): Regulatory sequences far from the promoter that increase or repress transcription Prokaryotes -35 and -10 (TATA) elements: Core parts of the promoter, recognized by the sigma factor of RNA polymerase. TSS (Transcription Start Site): Where transcription begins. 5′ UTR: Untranslated region before the coding sequence. CDS (Coding Sequence): Translated into protein. Terminator: Hairpin loop or Rho-dependent mechanism signals RNA polymerase to stop.

Answer 21

1. Closed Complex Formation RNA polymerase holoenzyme (core + σ) binds to the -35 and -10 regions of the promoter. DNA is still double-stranded at this point. 2. Open Complex Formation (Transcription Bubble) RNA polymerase unwinds about 17 base pairs around the -10 region. Forms a transcription bubble. The template strand is exposed and used for RNA synthesis. 3. Initiation of RNA Synthesis RNA polymerase begins adding ribonucleotides at the +1 site. The first few nucleotides are added without the polymerase moving. Sigma factor may still be bound. 4. Promoter Clearance After ~10 nucleotides are synthesized, the sigma factor dissociates. RNA polymerase transitions into elongation mode and moves downstream.

Answer 22

Steps in Elongation: RNA polymerase reads the DNA template strand from 3′ to 5′. It builds the RNA transcript in the 5′ to 3′ direction, complementary to the template strand. Uracil (U) replaces thymine (T) in RNA. - The template strand is what RNA polymerase reads (from 3′ to 5′). - The coding strand has the same sequence as the RNA (but T instead of U).

Answer 23

A gene is a segment of DNA that contains the instructions to make a functional product, usually a protein

Answer 24

Transcription: The process of copying a DNA sequence into RNA. Translation: The process of decoding an mRNA transcript to build a protein.

Unit 1 review Flashcards

(51 cards)