Chapter 6: Genes and Genomes

T/F: Genome size is related to genetic complexity

F

Define gene

a segment of DNA that is expressed to yield a functional product (ex. rRNA, tRNA, polypeptide)

What's the primary difference between exons and introns?

exons are coding sequences in genes, they are separated by noncoding sequences called introns

What are the roles of introns?

regulation of gene expression

expand coding potential by allowing genes to be expressed in different ways

T/F: Only exons are included in the mRNA

T

introns are removed by splicing

What types of eukaryotes lack introns?

histone genes

simple eukaryotes like yeasts

rarely found in genes of prokaryotes

Define alternative splicing

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

Introns encode what two types of functional products?

1. proteins

2. noncoding RNAs

Complex eukaryotic genomes contain highly ___ noncoding DNA sequences.

repeated

What are simple sequence repeats?

tandem arrays of short sequences (1-500 nucleotides)

What are satellite DNAs?

simple sequence repeats of DNA band as "satellites" separated from the main DNA band

Simple sequence repeats are not ___ but some play important roles in ___

transcribed

chromosome structure

Define quaternary structure

interactions between different polypeptide chains in proteins composed of more than one polypeptide

What is a gene family?

members of a group of related genes that may be transcribed in different tissues or at different stages of development

What is encoded by gene families?

alpha and beta subunits of hemoglobin

What are the differences between prokaryotic and eukaryotic genomes?

prokaryotes: single chromosomes, circular DNA

eukaryotes: multiple chromosomes, linear DNA

Define chromatin

complex of DNA and proteins (major proteins are histones)

What are the five major types of histones present in many different species of eukaryotes?

H1, H2, H2B, H3, H4

The ___ is the basic structural unit of chromatin.

nucleosome

DNA is wrapped around histones in ___ and sealed by ___

nucleosome core particles

histone H1

How do nonhistone proteins bind to DNA?

bind to linker DNA between nucleosome core particles

147 base pairs of DNA is wrapped around a histone core to form ___

nucleosome core particles

What forms a chromatosome?

histone H1 bound to DNA where enters nucleosome core particle

What core histones are in the histone core that makes up the nucleosome core particle?

two of each: H2A, H2B, H3, H4

What linker histone holds the base pairs around the histone core in chromatosome?

H1

What is euchromatin?

most chromatin, decondensed, distributed throughout nucleus

What is heterochromatin?

highly condensed, transcriptionally inactive, contains highly repeated DNA sequences

How does chromatin change as the cell leaves interphase and enters mitosis?

interphase: 90% euchromatin, 10% heterochromatin

mitosis: chromosomes become more condensed (more heterochromatin)

No ___ occurs during mitosis

transcription

What is the centromere?

specialized region of chromosome helps ensure correct distribution of duplicated chromosomes to daughter cells during mitosis

DNA is replicated during ___ resulting in two copies of each chromosome.

interphase

Describe metaphase chromosomes?

consist of two identical sister chromatids held together at centromere

How are sister chromatids separated?

microtubules of mitotic spindle attach to centromere and separate

then move to opposite poles

After the chromatids are separated and moved to separate poles what happens to the cell?

nuclear membrane reforms, chromosomes decondense

How is a kinetochore formed?

proteins bind to centromeres

spindle microtubules bind here

How is the movement of chromosomes directed?

proteins associated with kinetochores act as "molecular motors" to move chromosomes along spindle fibers

What are telomeres?

sequences at the end of chromosomes

required for replication of linear DNA

How do telomeres protect the chromosome termini from degradation?

bind protein complex (shelterin)

form loops at ends

Linear chromosomes can't be replicated by DNA ___. How do they replicate?

polymerase

telomerases use reverse transcriptase activity to replicate DNA

Maintenance of telomeres determines ___ and ___

lifespan

reproductive capacity of cells