Lecture 12

Question 1

1. Are all bacterial genomes dsDNA? Viral genomes? Eukaryotic genomes?

Question 2

2. Define the nucleoid region in bacteria.

Answer 2

the nucleoid region in bacteria is the region where genetic material is stored and made

Question 3

3. Give one similarity between H1 and HU proteins in bacteria and histones.

Answer 3

they are both bind via electrostatic interactions

Question 4

4. If a gene is present within a puff of a polytene chromosome, is it being transcribed?

Answer 4

spatial organization specifcally a puff indications that the gene is transcriptionally active

Question 5

What is one reason why histones are arginine and lysine rich?

Answer 5

the positive charges of lysine and arginine allow for electrostatic interactions with the histones thus stabilizing them

Question 6

Suppose endonuclease digestions of chromatin of a new eukaryotic species yielded fragments of
500 bp and multiples thereof. How would you interpret this?

Question 7

What are the 4 observations about histones

Answer 7

1. enzymatic digestion of histones by endonucleases occurs in multiples of 200 Bp, the endonucleases do not cleave within these intervals but after the 200bp intervals. The 200 bp intervals are where the nucleosomes are located and DNA wrapped around a histone cannot be cleaved
2. chromatin show a beads of strong structure( beads are nucleosomes(DNA wrapped around histones)
3. histone molecules were shown to form two types of tetramers with 4 different histone proteins
4. longer digestions with endonucleases leave only 147 bp fragments

Question 8

What components make up a histone octamer? A nucleosome core particle?

Answer 8

histone octamer is made of 8 histone proteins

nucelosome core particle is made of nucelosome +147 bp of DNA wrapped around

Question 9

. Define euchromatin and heterochromatin.

Answer 9

euchromatin is loosely packed dna that is transcriptionally active and heterochromatin is tightly packed and transcriptionally inactive

Question 10

Define repetitive DNA, Nongenic DNA, and transposable elements

Answer 10

repetitive DNA:
nongenic: DNA with no genetic function
transposable elements: are “jumping genes” that can replicate themselves and insert into a genome

Question 11

What fraction of the human genome encodes proteins?

Answer 11

2% if the genome encodes for proteins

Question 12

What are the four aspects of organelle inheritance that distinguish it from nuclear inheritance?

Answer 12

1. mutple organelles are present within single cells
2. each organelle can have multiple copies of the genome ( heterozygou/homozygous does not apply)
3. genome sizes and number of genes present in organelle genomes are widely variable
4. traits controller dby organellar inheritance are also influenced by nuclear genes

Question 13

If pollen from a variegated branch fertilizes an ovule from a white branch, what is the result?

Whatis the result of the reciprocal cross? What explains this difference?

Answer 13

1. the offspring will be white as well
2. with a reciprocal cross pollen would come from a white branch and ovule would from from a variegated branch. This would result in offspring that was varageiated, white, or green.

Question 14

Define homoplasmy and heteroplasmy.

Answer 14

heteroplasmy: mixture of normal and defective chloroplasts
homoplasmy: either have all mutant or all wildtype genomes

Question 15

. You hear a classmate say that homoplasmic cells give rise to homoplasmic cells and that
heteroplasmic cells give rise to heteroplasmic cells. Are they strictly correct? If not, Why?

Answer 15

they are not because heteroplasmic cells can give rise to heteroplasmic cells OR homoplasmic cells

Question 16

Explain why mitochondrial diseases often have variable penetrance and expressivity.

Answer 16

heteroplasmy can be a spectrum of mutant to wildtype; people vary in how heterplasmic they are for a mutation

Question 17

How does mitochondrial inheritance differ from Mendel’s parental reciprocal crosses?

Answer 17

mitochondrial inheritance is uniparental

Question 18

Why are mitochondrial diseases often more severe in males?

Answer 18

many mitochondrial diseases are pleiotropy ( affect many phenotypes)

mitochondria are only passed through females so male mitochondria have no evolutionary future and therefore natural selection can only act on mitochondrial mutations that affect the female lineage

the mitochondrial mutations in males however can be maintained

Question 19

Explain the idea of complementation within a cell with some functional mitochondria and some nonfunctional mitochondria.

Question 20

How are organelles inherited in Chlamydomonas? Who discovered the first chloroplast mutation
in this system?

Answer 20

Despite Chlamydomonas have isogamous gametes and thus contribute chloroplast to the zygote equally ONLY THE CHLORPLAST GENOME FROM THE MT + PARENT IS RETAINED

UNIPARENTL ORGENLLAR INHERITANCE

ruth sager discovered the first chloroplast mutation

Question 21

Why do “petite” mutants grow to a smaller size than wild type in yeast?

Answer 21

petites grow smaller as they can survive solely on anaerobic atp and since less atp is produced per glucose compared to ETC this results in smaller colonies

Question 21

You cross a petite strain to a wild type strain. Sporulation of the offspring yields two wild type and two petite spores. What type of mutation causes the petite phenotype in the parent and where is this
mutation located (mito or nuclear genome?)?

Question 22

Mitochondrial genomes vary vastly in genome content. Why are these genomes able to lose so
many genes in certain lineages?

Question 23

Why is representation of the “tree of life” not strictly accurate?

Question 24

What is secondary endosymbiosis? Contrast it with primary endosymbiosis.

Question 25

Which evolved first, the nucleus or the mitochondria? Explain the “mitochondrial” biology of Giardia duodenalis in your answer.

Question 26

What is an apicoplast? Why would a non-photosynthetic plastid ever be maintained?