How Genetic Information is Organized in the Genome

Describe difference in how the many genes are organized in the genomes of eukaryotes vs. prokaryotes

- as complexity of organism increases, space between genes increases

What is the problem with DNA that is bound to histones and compacted?

- chromatin fiber, when complexed with histones and folded into various levels, makes DNA inaccessible to interaction with important nonhistone proteins

euchromatin

- chromatin/chromosomal regions that are lightly staining and relatively uncoiled during interphase portion of cell cycle

Characteristics of viral chromosomes

- circular - linear - made of DNA (single or double-stranded) - made of RNA (single or double-stranded

Characteristics of bacterial chromosomes

- circular - made of DNA (single or double-stranded)

Where would you find circular vs. linear chromosomes?

- circular -- virsuses, bacteria, mitochondria, chloroplasts - linear -- eukaryotes, viruses

Exon

- contains the information for the structure of the expressed protein - doesn't get spliced out

How is DNA packaged into a chromosome?

- done in several steps, starting with double helix of DNA, then DNA wrapped around some proteins - these proteins are packed tightly together until they form a chromosome...chromosomes are efficient storage units for DNA

What is telomerase and what cells express this protein?

- enzyme that adds bases to ends of telomeres - remains active in sperm and eggs (reproductive cells)

T/F: STRs and VNTRs do no code for genes.

- false

heterochromatin

- heavily staining, late-replicating regions of chromosomes that are prematurely condense in interphase - found in eukaryotes

What are the proteins associated with DNA in eukaryotes? What is their purpose?

- histones -- highly alkaline proteins in eukaryotic cell nuclei that package and order the DNA into structural units (called nucleosomes) - chief protein component in chromatin, and act as spools around which DNA winds, and play role in gene function

regulatory region (promoter)

- information on where and when a gene will be transcribed during development - usually upstream of the coding region

Where are telomeres located on a chromosome? How many telomeres are there on each chromosome?

- located at ends of the chromosomes -- protect our genetic data, make it possible for cells to divide - 4 telomeres (one at each end)

CEN region

- minimal region of centromere that supports function of chromosomal segregation - DNA binds a platform of proteins, which in multicellular organisms includes kinetochore that binds spindle fiber during division

Eukaryotic cells contain DNA in the mitochondria and chloroplasts (in addition to nucleus). Is the organizatio of DNA in these organelles more similar to bacteria or eukaryotic chromosomes?

- more similar to bacteria because exist as double-stranded closed

Are the number of genes proportional to genome size?

- no - noncoding/repetitive DNA in humans explains this

Can we predict relative genome size based on the complexity of the organism?

- no - plants have biggest, prokaryotes have smallest

Is bacterial DNA compacted tightly around histones, like in eukaryotic cells?

- no, they are compacted around several types of DNA-binding proteins

In eukaryotes, DNA and its associated proteins are called: __________

- nucleosomes - genes are more actively expressed in less tightly packed regions of chromosomes

Where are chromosomes found in cell?

- nucleus -- eukaryotes, viruses - part of cytoplasm -- bacteria - mitochondria, chloroplasts -- circular

What does DNA sequence look like at telomere?

- sequences of DNA made of 4 nucleic bases (C, G, T, A) - made of repeating sequences of TTAGGG on one strand and AATCCC on other strand (repeat of six base pairs)

If the sequence was much shorter, such as GA and repeated 50 times in tandem, this would be known as a _____________.

- short tandem repeats (STR) - aka microsatellites

centromere

- specialized heterochromatic chromosomal region at which sister chromatids remain attached after replication - also site to which spindle fibers attach to the chromosome during cell division

When does a telomere shorten? What is the consequence of shortening telomere?

- telomere shortens each time a cell divides - when get too short, cell can no longer divide; it becomes inactive or "senescent" (it dies) -- shortening process associated with aging, cancer, and increased risk of death

termination

- the "stop" signal for where transcription should end - downstream of coding region

LINES and SINES are longer sequences and they do no repeat in tandem. Why are they called repetitive?

- they are still individually dispersed throughout the genome and repeat in same pattern (just not right next to each other)

Why would chromatin need to be remodeled?

- to accommodate these protein-DNA interactions, chromatin must be induced to change its structure (called chromatin remodeling)

A sequence such as TATAGCGTAGCTAGCT repeated in tandem (next to each other) 75 times is an example of a _______________________.

- variable number tandem repeat (VNTR) - aka ministaellites

- How many chromosomes are in a cell?

46 for humans, different for other organisms

T/F: The length of a species telomeres predicts the lifespan of that species.

True