(1) Chapter 6: Genes and Genomes

Question 1

Noncoding DNA

Answer 1

• most eukaryotic genomes contain large amounts of noncoding
• differences in sizes of eukaryotic genomes are reflected by amounts of noncoding DNA
• play roles in regulation of gene expression
• allow genes to be expressed in alternate ways

Question 2

Exons

Answer 2

coding sequences in genes

Question 3

Introns

Answer 3

• noncoding sequences in genes
• make up more that 90% of avg. human gene
• present in most complex eukaryotes
• not found in most simple eukaryotes ( like yeasts)
• rare presence in prokaryotes.

Question 4

Describe the mRNA relation to introns and exons

Answer 4

entire gene is transcribed to RNA but introns are removed by splicing, so that only exons are included in mRNA

Question 5

Histone genes

Answer 5

lack introns

Question 6

Alternative splicing

Answer 6

introns allow exons of a gene to be joined in different combinations, results in different proteins from the same gene

Question 7

Repetitive DNA sequences

Answer 7

• complex eukaryotic genomes contain highly repeated noncoding DNA sequences
• can be present in hundreds of thousands of copies

Question 8

simple sequence repeats

Answer 8

-consists of tandem arrays of up to thousands of copies of short sequences, ranging from 1 to 500 nucleotides

Question 9

How can simple sequence repeats be separated?

Answer 9

• by equilibrium centrifugation in CsCl density gradients
• AT rich sequences are less dense than GC rich sequences.
• These repeat sequence DNAs band as satellites

Question 10

Satellite DNAs

Answer 10

repeat sequence DNAs seperate from the main band of DNA (in simple sequence repeats)

• not transcribed
• some play important roles in chromosome structure

Question 11

What can multiple copies of eukaryotic genes be used for

Answer 11

-to produce RNAs or proteins in large quantities, like ribosomal RNAs or histones

Question 12

gene family

Answer 12

• a group of related genes

- members may be transcribed in different tissue or at different stages of development

Question 13

Encoding of alpha and beta subunits of hemoglobin

Answer 13

encoded by gene families; different members of these families are expressed in embryonic, fetal, and adult tissues

Question 14

Theory of gene family rise

Answer 14

-duplication of an original ancestral gene, followed by mutation and divergence of different family members.

Question 15

What is the result of gene family presence?

Answer 15

• proteins optimized for different functions

- some mutations result in loss of function

Question 16

Pseudogenes

Answer 16

nonfunctional gene copies

Question 17

Gene duplication rise

Answer 17

1. duplication of DNA segment results in transfer of a block of DNA to a new location in genome
2. retrotransposition

Question 18

Retrotransposition

Answer 18

• duplication by reverse transcription of an mRNA followed by integration of the cDNA copy into a new chromosomal site
• results in an inactive gene copy called a processed pseudogene

Question 19

processed pseudogene

Answer 19

lacks introns and the normal sequences that direct transcription

Question 20

Chromatin

Answer 20

• a complex DNA and proteins, major proteins present are histones
• has many other proteins that are involved in replication and gene expression

Question 21

Five major types of Histones

Answer 21

H1, H2A, H2B, H3, H4

Question 22

Nucleosome

Answer 22

basic structural unit of chromatin

Question 23

How is chromatin arranged in nucleosomes

Answer 23

DNA is wrapped around histones in nucleosome core particles and sealed by histone H1. nonhistone proteins bind to linker DNA between nucleosome core particles

Question 24

How many bp’s of DNA are wrapped around a histone core? what does this form?

Answer 24

• 147 base pairs

- forms nucleosome core particles

Question 25

Chromatosome

Answer 25

histone H1 is bound to DNA where it enters the core particle.
(DNA is wrapped around a histone core to form nucleosome core particles)

Question 26

Structure of a nucleosome core particles

Answer 26

• nucleosome core particles contain 147 base pairs of DNA that are wrapped 1.67 turns around a histone core
• histone core consists of two each of H2A, H2B, H3, and H4

Question 27

Chromatosome structure

Answer 27

• 166 base pairs of DNA (2 full turns

- DNA wrapped around histone core and held in place by H1 (linker histone)

Question 28

Chromatin fibers

Answer 28

• packaging of DNA with histones yields a chromatin fiber
• ~10nm in diameter, shortens length x6
• condensed by coiling into 30nm fibers
• total condensation= x50

Question 29

Euchromatin

Answer 29

• makes up the most chromatin in interphase

- relatively decondensed and distributed throughout the nucleus

Question 30

Heterochromatin

Answer 30

• about 10% of interphase chromatin
• very highly condensed
• resembles chromatn of cells undergoing mitosis
• trancriptionally inactive and contains highly repeated DNA sequences

Question 31

Centromere

Answer 31

• specialized region of chromosome that helps ensure correct distribution of duplicated chromosomes to daughter cells during mitosis.
• DNA sequences to which proteins bind
• form kinetochore

Question 32

Kinetochore

Answer 32

form at center of chromatid pair

• where spindle microtubules bind
• proteins associated with the kinetochore act as molecular motos to srive the movement of chromosmes along spindle fibers

Question 33

Telomeres

Answer 33

• sequesnces at end of chromosomes
• required for replication of linear DNA molecules
• end with 3’ overhand of single stranded DNA
• telomeres of some organisms (including humans) form loops at ends
• maintenance determines lifespan and reproductive capacity of cells

Question 34

Sheltrin

Answer 34

a protein complex that binds to telomere to protect the chromosome termini from degradation

Question 35

Telomerase

Answer 35

-uses reverse transcriptase activity to replicate telomeric DNA sequences since the ends of linear chromosomes can’t be replicated by DNA polymerase.