Genetics Exam 4

Telomerase

Type of DNA Polymerase capable of syntheszing the telomeres of a chromosome in eukaryotes

Hayflick’s Limit

The point where a chromosome has undergone so many rounds of the cell cycle to the point where the chromosome is too short to continue replicating, triggering apoptosis

(the cell cycle shortens the chromosome with each round)

(showcases the immortal nature of eukaryotic cells)

Progeria

Condition of having defected telomerase, causing rapid aging

• causes premature apoptosis

• often De Novo

• Mutation in LMNA gene

De Novo

The first in the family to have a disease (not inherited)

Types of DNA (6)

B-DNA

A-DNA

Z-DNA

D & E - DNA

P-DNA

B-DNA

• Majority of DNA

• 10 rungs per turn

• Watson and Crick proposal

A-DNA

• double stranded RNA

• 8 rungs per turn

• found in DNA-RNA hybrid (transcription)

Z-DNA

• 12 rungs per turn (most compact form of DNA)

• Zig-Zag pattern that is not smooth

• Highly methylated and found in Barr Bodies

D and E - DNA

• both lack Guanine

• 8 rungs per turn (D)

• 7.5 rungs per turn (E)

P-DNA

2.62 rungs per turn

DNA Denaturation

• the non-covalent hydrogen bonds break when heated, causing strands to separate since the base pairs are no longer binded

• G-C bonds require more heat to break since they have 3 H-bonds opposed to 2 (A-T)

  • In comparision, the species with a higher melting point has more G-C BPs

DNA Renaturation / Annealing

Requires Proper Conditions:

1. Temperature must be 25°C below the melting point

2. DNA Concentration: the higher the DNA concentration, the higher the chance the BPs will anneal

higher concentration = faster annealing

1. Renaturation Time: The longer the time allowed, the better the chance of annealing

Organization of DNA in Cells

• 70% of the eukaryotic genome functions to direct protein synthesis (hormones)

• at rest, the function is unknown

Types of Organizaton of DNA in Cells (3)

1. Repetitive DNA Sequences

   1. Highly Repetitive: same 5-15 BPs over 100k times

   2. Moderately Repetitive: same 1000-1500 BPs for 10-3000 times

1. Transposons / Jumping Genes

   1. transposons carry a gene allowing them to move genes (antibiotic resistance)

   2. McClintok discovered them in corn in the 1950’s, and have since been found in humans and flies.

2. Intervening DNA sequences / Interrupting Genes:

   1. Exons: interrupting gene that is expressed in protein production

   2. Introns: interrupting gene that is not expressed in protein production

Gene Expression (Gene → Protein)

Definiton: a genetic sequence that yields a product, usually a protein or hormone

The Steps:

1. Transcription: DNA serves as a template for the formation of RNA

2. Translation: the mRNA codons are translated into amino acid sequences that become proteins (synthesis of a polypeptide)

DNA Content per Haploid Cells and C-Value Paradox

• More complex organisms have higher levels of each

• forgs and lllies have more DNA than humans

• organsms have large C-Values due to extra non-coding DNA

Retroviruses

• RNA based viruses

• RNA → DNA → mRNA → Protein (reversed central dogma)

True/False: The template strand is a replica of the mRNA strand w/ the exception of uracil instead of thymine

False: the non-template strand is the replica, including this exception.

Archibald Garrod

• suggested that genes dictate phenotypes through enzymes that catalyze reactions

• Alkaptoneurea: condition of dark urine when in contact with the air, due to a lack of the ezyme responsible for metabolizing Alkapton.

• Inference: specific genes direct the synthesis of proteins. If there’s a genetic mutation, the protein will be improperly synthesized and will show in phenotypic expression.

Beadle & Tatum

• demonstrated the gene-protein relationship by studying mutants of Neurospora Crassa (bread mold)

• “One Gene - One Enzyme Polypeptide Hypothesis”

  • if theres a gene defect, there is a phenotypic enzyme defect that manifests into disease

Types of RNA

rRNA

• RNA Polymerase I

• 80% of total RNA

mRNA

• RNA Polymerase II

• 5% of total RNA

tRNA

• RNA Polymerase III

• 15% of total RNA

Promotor Region

Specific DNA sequence that RNA Polymerase binds onto, intiating transcription

Stop Codons

UAG

UGA

UAA

Start Codon

AUG

august

tRNA

• 15% of total RNA

• Synthesized by RNA Polymerase 3

• Translates codons into Amino Acids within the ribosome during protein synthesis

Does Helicase unwind the helix during transcription?

No

• RNA Polymerase separates the strands during transcription

• Helicase separates the strands during DNA replication

Transcription Unit

Initiating Sequence [ including TATA Box] + Terminating Sequence + Nucleotides in between

Relationship between Promoter Region, TATA Box, and Transcription Factors

The TATA Box is within the promoter region, where transcription factors bind onto it to signal RNA polymerase to start transcription

What are transcription factors

proteins that bind onto the promoter region, signalling RNA Polymerase to initiating transcription

TATA Box

• located 25 nucleotides into the promoter region

• alanine and thymine rich

3 Phases of Transcription

1. Initiation (TATA Box, Promoter Region, RNA Polymerase unwinding)

2. Elongation (RNA Polymerase adds mRNA BPs onto template strand (uracil) )

3. Termination (RNA Polymerase reads the terminator (AAUAA) )

Primary Transcript / Pre-mRNA

RNA molecule that still contains exons and introns

• before RNA splicing

• does not have 5’ cap or 3’ Poly-A-Tail

Mature mRNA

• after RNA splicing

• contains 5’ Cap (Guanosine Triphosphate)

• contains 3’ Poly-A-Tail

RNA Splicing

process that removes introns and ligates exons

Where is the site of transcription?

the nucleus

Where is the site of translation?

the cytoplasm, specifically

• ribosomes

• rough ER

Guanyl Transferase

the enzyme that initiates the capping of the 5’ region in pre-mRNA

Poly-A-Polymerase

enzyme that catalyzes the addition of adenosine onto the 3’ end, creating the Poly-A-Tail