Nucleotides + human genome Flashcards

Question

Explain the temperature dependence of denaturation.

Answer 1

base pairs seperate when **melting temperature T_M** reached ⇒ 50% hyperchromicity reached at ~ 70°C _NOTE:_ **increased T_M in DNA rich in G-C** (3 H-bonds instead of 2 as for A-T pairing) → more stable

Answer 2

**lower [cations]** decreases T_M b/c **increased interchain repulsion btw neg. charged phosphates** of phosphodiester backbones → increased denaturation

Answer 3

happens when physiological temperature/salt concentration regained 1. joining of short, homologous sites on two strands → **fast** 2. reversible zipping of repeated sequences → **slightly slower** 3. zipping of single copy base pairs → **slow**

Answer 4

ssDNA can form double stranded **hybrid molecule** w/ non-DNA molecule, such as **complementary RNA**

Answer 5

parent DNA molecule denaturates, so that **each strand can serve individually as template for the synthesis of a new complementary DNA strand** ⇒ 2 identical, daughter DNA molecules created proven by _Meselson-Stahl experiment_ using "heavy" ¹⁵N DNA

Answer 6

_nuclear (+ mitochondrial genome)_ * **30%** of DNA transcribed into RNA (introns + exons) * **2% are exons**, coding for proteins, rRNA, tRNA (approx. 25,000 protein coding genes) * **50%** are repetitive sequences * **20%** not categorized yet _NOTE:_ much more proteins (150 - 200k) can be synthesized due to _alternative splicing_

Answer 7

* **intron** = region of DNA that does not code for protein * **exon** = region of DNA that codes for protein → introns cut out for protein synthesis during process called _splicing_

Answer 8

* **SSR**s (simple sequence repeats): * repetitive sequences (2-500 bps) * **STR**s (short tandem repeats): * very short repetitive sequences (2-5 bps) * _satellite DNA, microsatellites_ * can be used for paternity tests, forensics * **clustered repeats:** * form _centromeres and telomers_ of chromosome

Answer 9

_group of interspersed repeats_ gene sequences that are **able to change position in genome** (form an RNA intermediate, _reverse transcriptase_ forms again DNA) * make up approx. _45% of entire genome_ * 2 groups: **_SINE_**s and **_LINE_**s (short/long interspersed nuclear elements)

Answer 10

**_single nucleotide polymorphism_** chromosomes of diff. individuals identical for most DNA sequences → SNPs are _variations of single bases_

Answer 11

* source of information for _synthesis of protein molecules_ * information _inherited by offspring_

Answer 12

complex of macromolecules in **eukaryotic cells**, packaged into chromosome _consists of:_ * **dsDNA** (= double stranded) * **histones**: condense DNA * **non-histone proteins**: enzymes resp. for DNA replication, repair, transport process of RNA * **RNA**

Answer 13

* *haploid** = number of chromosomes, in a gamete * *diploid** = number of chromosome _pairs_, in somatic cells * _22 autosomal_ chromosomes (number 1-22) * _1 gonosomal_ chromosome (either X or Y)

Answer 14

structure depends on stage of cell cycle * **euchromatin** = accessible ("turned on") chromatin that is actively transcribed _during interphase_ * **heterochromatin** = highly condensed chromatin, w/ lower level of "activating" histone PMTs, untranscribed ("turned off"), either: * **constitutive**: always inactive * **facultative**: can be converted to euchromatin

Answer 15

compact transportable form, forming classical 4 arm structure 1. dsDNA 2. winds around **histones** to form **nucleosome →**"beads-on-a-string" (_10-nm chromatin fibril_) 3. supercoiled fibrils form **30nm-chromatin fiber** 4. forms more and more supercoils ⇒ eventually _2 sister chromatids_ connected at _centromere_, terminally attached _telomeres_

Answer 16

2 homologous chromosomes align and chromatides exchange genetic information → **recombination** ⇒ incr. g_enetic variation_, one mechanism how evolution happened

Answer 17

basic unit of DNA packaging in eukaryotes, consisting of * a segment of DNA wrapped around **eight histone protein core** _twice in left-handed fashion_ * connected to next "core particle" by stretches of **linker DNA** ****_NOTE:_ H1 associates individually w/ DNA at each octomer

Answer 18

decrease in size/molecular weight w/ increasing number (1 = largest/heaviest, etc.) * **H1** = stabilizes 30-nm chromatin fiber, associates w/ DNA at each octomer * **H2A + H2B** = form dimer * **H3 + H4** = form tetramer ⇒ 2 dimers + 1 tetramer form _histone octomer core of nucleosome_

Answer 19

**do NOT contain introns**, are fully transcribed, unspliced

Answer 20

preference of nucleosomes to certain regions

Answer 21

**energy is stored** in supercoils (= torsional stress) → transition to another form that needs energy provided by **underwinding** * **negative supercoils:** DNA twisted in direction opposite from the clockwise turns of B-DNA (ergo: left-handed)

Answer 22

* in **mitochondria** * in **bacteria, bacteriophages** * in many **DNA-containing animal viruses** ⇒ either in _relaxed_ or _supercoiled form_

Answer 23

_tiny part of human genome_ 37 genes coding for: * **2 mito.-specific rRNAs** * **22 mito.-specific tRNAs** * **13 proteins** that play an important role in the resp. chain ⇒ inherited maternally, hence _passed on to all children_

Answer 24

* strands different in base composition → **1 H (heavy) + 1 L (light) strand**, _more genes encoded on H strand_ * **D (displacement) loop** = DNA triple helix w/ 2 overlapping copies of H strand, _most of replication/transcription controlled_ here * **no introns**