Exam 3 Flashcards
RNA polymerase
- Holoenzyme that finds which gene to transcribe, and begins the process of transcription
- no primer is necessary to begin transcription
- has 4 subunits bound to a core enzyme
- Sigma Factor plays role in regulatory function
- 3 types to synthesize the 3 types of RNA.
- RNA polymerase synthesizes mRNA,
- DNA polymerase synthesizes DNA
Centromere
- region of a chromosome where spindle fibers attach
- chromosomes without a centromere would be lost
- important for chromosomal segregation
Chromatin Remodeling
- structure must change to allow access to DNA
- ability to package DNA while maintaining structure, and be able to go back in and change structure to access the DNA
- ESSENTIAL
- histone tails, acetylation, methylation and phosphorylation
DNA is a ________ and nucleotides are the building blocks of these molecules
- nucleic acid
Direction of B form DNA (watson and crick)
- 5’ to 3’ direction (Watson)
- 3’ to 5’ direction (crick)
- antiparallel to eachother
Ribozymes
- catalytic RNA (function as enzymes)
Elongation in bacterial transcription
- RNA polymerase
- unwinding of DNA ahead of transcription bubble and rewinding behind it - 5’ to 3’ extension of RNA
- DNA/RNA duplex within the bubble
How do you remove introns (noncoding regions)?
- Pre-mRNA undergoes splicing in the nucleus
- Requires 3 sequences:
1. a 5’ splice site
2. a 3’ splice site - a 5’ and 3’ splice site defined by GU, end in AG
3. branch site- 18 to 40 nucleotides upstream of 3’ splice site (Y-pyrimidine and R-Purine) - Splicesome is ESSENTIAL!!! It’s made of RNAs and proteins and it cuts out introns
G banding
- Stains condensed chromosomes to create a visual karyotype
- photographs the entire chromosome complement
Alternative Splicing
- yielding different transcripts from the same gene via mRNA processing
- moves around the exons to decide which ones will get expressed
- adds variation
Transposable sequences
- “jumping genes” that move around and insert themselves to cause mutations
- mobile and can potentially relocate within the genome
- make up a HUGE portion of the human genome
Prokaryotic DNA structure
- DNA without free ends can become supercoiled positive and negative
- most DNA are negatively supercoiled (with the help of topoisomerase)
- separation of strands is easier, occupies less space then relaxed
Difference between eukaryotic and bacterial DNA
- bacterial DNA is packed with proteins instead of histones
- are much smaller in size
- are often circular
What does insertion of the wrong nucleotide lead to?
- the incorrect positioning of 3’ OH which stalls polymerase
Polytene chromosome
- specialized chromosomes that do not exist in every organism
- Can be seen under microscope during interphase
many stranded chromosome - has undergone DNA replication without the separation of the replicated strands, which remain in exact parallel register
- large banded chromosomes that came about during chromosomal REPLICATION WITHOUT DIVISION
- Line up with each other at chromomeres (centers)
- have puffs at certain chromomeres
Do most somatic cells have telomerase activity?
NO
- we have a copy of the gene, but it’s usually turned off and inactive
- This means our telomeres are shortening w/ every replication as we age
Heteromeric Codons
- codons that have different ribonucleotides in them
- EX: ACA instead of just AAA
- We know that a codon is made of 2 A’s and 1 C, but we don’t know the exact order (exact codon)
- ACA, AAC, CAA are all possible
What is the eukaryotic origins for DNA replication
- ARS (autonomously replicating sequences)
- enable DNA to replicate
- there are many
Linear eukaryotic Replication
- eukaryotes
- has multiple origins(replicons)/ replication forks and bubbles
- do not break the nucleotide strand
- forms 2 new linear DNA strands
- bidirectional
Nucleoside
- consists of only a pentose sugar and nitrogenous base
- NO phosphate group
Denaturation of DNA
- MELTING DNA to pull strands apart by breaking hydrogen bonds between nitrogenous bases
RNA splicing
- Removes noncoding introns from pre-mRNA
- facilitates export of mRNA to cytoplasm
- Allows for multiple proteins to be produced
A-DNA form
- alpha helix (right handed/clockwise spiral)
- shorter/wider
- probably does not exist in nature
positive supercoil
- adding in rotations to circular DNA which causes supercoiling