2. Genomics

Question 1

The Human Genome contains fewer genes than expected (20,000) in comparison to # of proteins we have. Why?

Answer 1

Many human genes produce more than one protein through alternative splicing
* Number of proteins produced (around 200,000) much larger than the number of genes than encode for them.

Question 2

Parts of a Chromosome

Centromeres:

Answer 2

• Made of DNA (heterochromatin)
• Constricted region that separates chromosome into short arm (p) and long arm (q)

Question 3

Kinetochore

Answer 3

• Made of protein
• Bind both centromere and spindle fibers
• Inner Kinetochore facing CENP-A
• Outer Kinetochore facing spindles

Question 4

CENP-A:

Answer 4

• Centromere-specific Histone
• Centromeres have a special nucleosome where Histone3 is substituted another histone called CENP-A
• Helps kinetochores attach at the right place

Slide 9

Question 5

Types of Chromosomes

Telocentric

Answer 5

Centromere with one arm coming off parallel on both sides. (only 2 arms total)
* LOOKS LIKE A U

Question 6

Types of Chromosomes

Acrocentric

Answer 6

Two long arms and two satellites
* Looks like alien antennas

Question 7

Types of Chromosomes

Submetacentric:

Answer 7

Two long arms and two short arms
* Typical human chromosome

Question 8

Types of Chromosomes

Metacentric:

Answer 8

4 long arms
* Centomere exactly in middle

Question 9

Parts of a Chromosome:

Telomeres:

Answer 9

Natural ends of a chromosome
* Highly repetetive sequence (CCCTAA / TTAGGG)

Question 10

Telomere 3’ Overhang and Loops:

Answer 10

• G-rich strand
• Single-stranded G-Tail
• Telomere forms loops because nature of G-tail can complement internal tracks of telomere sequence
• TELOMERE SPECIFIC PROTEINS recognize telomere sequence. BINDS TELOMERES and assist in formation of loop

Question 11

3’ Overhang Issue:

Answer 11

Telomeres loop (t-loop) to protect chromosome ends from degradation by DNA repair enzymes. 3’ Overhang is inserted back into the DNA of the chromosome.

Question 12

Telomeres recognized by a series of proteins:

Answer 12

1. Telomere specific protein: TRF1 and TRF2
2. Telomere non specific proteins: Ku

Question 13

Main function of telomeres is protecting chromosome from:

Answer 13

• Exonucleases
• DNA Repair
• Recombination

Question 14

Telomere problem:

Answer 14

Gets shorter every cell cycle
* As cells divide over time, telomeres shorten, and eventually cell division stops.
* SHORTENING LEADS TO: unprotected chromosome ends

Question 15

Telomerase:

Answer 15

Enzyme that can extend telomere ends.
* Uses bound RNA template to go to G-Tail and add to the Tail.
* Needed at beginning of fetal development

Question 16

Intergenic regions:

Answer 16

Non-repetitive DNA where many regulatory sequences are located
* In neither introns nor codons

Question 17

Highly Repetitive DNA

Answer 17

Sequences less than 10bp present HUNDREDS of THOUSANDS to MILLIONS of times
* EX: Telomeres (TTAGGG)
* EX: Satelites

Question 18

Moderately repetitive DNA:

Answer 18

Sequences 150-300bp present THOUSANDS of times
* EX: ALU elements (transposable elements)

Question 19

Tandem Repeats:

Answer 19

Repeats placed one after another in CLUSTERS in SPECIFIC REGIONS of genome.
* EX: rRNA and t-RNA

Question 20

Interspersed Repeats:

Answer 20

Repeats scattered throughout the genome

Question 21

Ribosomes:

Answer 21

Make protein
* complexes of rRNA molecules and proteins
* synthesize proteins by translating genetic code transcribed in mRNA into an amino acid sequence

Question 22

Nucleolus Oragnizer Regions (NOR):

Answer 22

• contain the genes for ribosomal RNA (rRNA) and give rise to the interphase nucleoli
• consist of tandemly repeated sequences of rRNA genes
• located on the short arms of the acrocentric chromosomes 13, 14, 15, 21, and 22, and they code for 5.8S, 18S, and 28S ribosomal RNA

Question 23

Nucleolus and NORs:

Answer 23

• During interphase, the nucleolus is a prominent structure located within the nucleus of a cell. It is responsible for producing and assembling the cell’s ribosomes
• The nucleolus is composed of regions called nucleolar organizer regions (NORs), which contain the genes responsible for producing ribosomal RNA (rRNA)

Question 24

Transposons:

Answer 24

DNA sequences that can insert themselves in other parts of genome

Question 25

Class I: Retrotransposons:

Answer 25

Requires reverse transcriptase to jump from one site of genome to another.
* Most abundant in our genome. 42%!
* Mutagenic bc can insert in any region of our genome

Question 26

Class II: DNA Transposons:

Answer 26

Do not require reverse transcriptase. Jump as DNA thanks to transposase enzyme encoded in the transposon.
* ~10% of genome