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PCB 3063 Exam 3 Study Guide Solutions The 1˚and 2˚molecular structure of DNA - ANSWER-Its function: to store, replicate, and transmit genetic information The 3˚structure of DNA - ANSWER-Determines its ability to express the encoded information as a phenotype DNA's 3˚structure must be flexi...

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  • October 30, 2024
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PCB 3063 Exam 3 Study Guide Solutions


The 1˚and 2˚molecular structure of DNA - ANSWER✔✔-Its function: to store, replicate, and transmit

genetic information


The 3˚structure of DNA - ANSWER✔✔-Determines its ability to express the encoded information as a

phenotype


DNA's 3˚structure must be flexible and dynamic - ANSWER✔✔-A vast amount of genetic information

must be packed into a cell of limited size


This material must be tightly condensed for chromosomes to move as individual units during cell division


But DNA must be de-condensed at other times to be accessible for replication and transcription.


Genome size - ANSWER✔✔-The genomes of different species contain different amounts of DNA.


The complexity of an organism doesn't necessarily match the amount of DNA in its genome


Humans have a 6 billion base pair genome


a single-celled protist, Polychaos dubium, has the largest genome of all organisms with 670 billion base

pairs



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Regardless of genome size, all organisms must contain their genetic information inside the cell


Levels of DNA structure: Primary - ANSWER✔✔-Nucleotide sequence


Levels of DNA structure: Secondary - ANSWER✔✔-Double helix of antiparallel strands


Levels of DNA structure: Tertiary - ANSWER✔✔-Folding and packing to fit in confined space of cell


Relaxed helical DNA - ANSWER✔✔-Not supercoiled.


10 turns = 100 bp of DNA


The lowest energy state is B-DNA with 10 bases per turn


Supercoiling - ANSWER✔✔-Stress on the helix that over-winds or under-winds it will cause the helix to

twist back on itself


Positive supercoiling - ANSWER✔✔-Over-rotated


Negative supercoiling - ANSWER✔✔-Under-rotated


Topoisomerases - ANSWER✔✔-Enzymes that can add or remove a turn in DNA by breaking sugar-

phosphate backbone, rotating, and then rejoining ends


Most DNA is negatively supercoiled - ANSWER✔✔-Helps pack DNA into small space


Strand separation during replication and transcription is more rapid and requires less energy

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Most Bacterial genomes are contained in a single circular chromosome - ANSWER✔✔-Bound proteins

help compact the DNA circle into supercoiled loops in the nucleoid region of the cell


Many bacteria also have additional DNA in small circular, plasmids that replicate independent of the

chromosome


Eukaryotic Chromosomes - ANSWER✔✔-The multiple linear chromosomes in a eukaryotic nucleus are

highly condensed


Degree of coiling and packing changes throughout cell cycle


Interphase: relatively more relaxed = less condensed


Mitotic phase: relatively more compact = fully condensed for movement of individual chromosomes

during cell division


Chromatin - ANSWER✔✔-DNA complexed with proteins; 2 types


Euchromatin - ANSWER✔✔-Will become more condensed and less condensed during different stages of

the cell cycle, making DNA more and less accessible for transcription


Heterochromatin - ANSWER✔✔-Remains highly condensed throughout cell cycle, preventing most

transcription




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Constitutive: Permanent; telomere and centromere regions


Facultative: Changeable condensation; X-inactivation


Most chromatin is composed of histone proteins - ANSWER✔✔-5 types: H1, H2A, H2B, H3 & H4


Histones contain a large proportion of positively-charged arginine and lysine amino acids


DNA is composed of negatively-charged phosphates, so histones are attracted to and bind tightly to DNA


Nucleosomes - ANSWER✔✔-"Beads" made of DNA wrapped 2x around 8 histone proteins (2 each of

H2A, H2B, H3 & H4)


Each histone has a positively charged "tail"


Chromatosomes - ANSWER✔✔-Histone H1 (not in the octet), binds to wrapped DNA to clamp

nucleosome in place: nucleosome + H1


Linker DNA - ANSWER✔✔-Stretches of DNA between nucleosomes


Change in Chromatin Structure & Transcription - ANSWER✔✔-For DNA to be transcribed, chromatin

structure must relax to allow access for the transcriptional enzymes


Chromosome puff - ANSWER✔✔-Drosophila giant polytene chromosomes


A localized swelling of relaxed chromatin



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