DNA and Chromosomes (Week 2) Flashcards
What are genes?
How many genes for the expressed human genome?
- genes are segments of DNA that encode proteins
- not many; only about 1.5% of the human genome
What is a chromosome?
- long continuous piece of DNA containing many genes (contains many genes, regulatory elements and other intervening nucleotide sequences)
- eukaryotes chromosomes are structurally complex and are wrapped around proteins (histones)
- only eukaryotes have chromosomes
What is chromatin? How long is the short region of the DNA double helix?
- chromatin is DNA wound around proteins
- DNA is about 2nm long
What is karyotyping? what is a karyogram?
- karyotyping is a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells
- a karyogram is the picture that you see of all the homologous pairs of chromosomes lined up
What is the flow of information in cells (hint Central Dogma)?
Within cell: DNA is in the nucleus and mRNA is transcipted in the nucleus
-this mRNA is then moved to the cytoplasm where ribosomes will translate it to make a a protein
Between Generations: DNA replication occurs in the nucleus before mitosis. It must be perfect or there will be errors
What is the DNA structure? Who discovered it?
- Waston and Crick in 1952
- Double helix with sugar phosphate backbone and nitrogenous bases connected by H bonding
- DNA is anti-parallel (starts at 5’ ends at 3’)
What are Chargaff’s rules?
A=T (form 2 bonds) and G=C (form 3 bonds)
-harder to pull appart GC bonds
the number of purines (A,G)= the number of pyrimidines (C,T,U)
What is important about DNA’s structure? Why?
- it has two forms: relaxed and super-coiled
- seen in circular DNA and also in linear DNA
- this helps DNA become for compact
What are topoisomerases? What is used in bacteria
-super-coils can form when compacting DNA
-enzymes that regulate the over-winding or under-winding of DNA
2 types: on for single strand breaks; two for double strand breaks (bacteria uses DNA gyrase); this one requires energy to work
What can be noted about the Double helix structure?
-anti parallel strands starting at 5’ end at 3’ (left)
(right goes 3’ to 5’)
-lots of CG makes it harder to separate the strands
-each strand acts as a template strand for the other strand
-phosphodiester bonds join carbon 5 with carbon 3
What’s the different between a nucleoside and and nucleotide?
- side: Base and Pentose
tide: Base and Pentose and Phosphate group
What does DNA consist of (what are nucleotides made of)?
- nucleotide: one of the bases A,G,C,T or U(RNA)
- pentose sugar molecule
- phosphate group
What is the difference in the forms of DNA (B-DNA, Z-DNA, and A-DNA)?
B-DNA: normal form; right handed DNA
Z-DNA: Zig-zag left-handed helix; longer and thinner than B-DNA
A-DNA: Right-handed helix; shorter and thicker than B-DNA; can be artificiality by dehydrating B-DNA
-RNA if double helix
-wide minor groove and narrow major groove
What affect does super coiling have on the DNA molecule?
- it affects the spatial organization and the energy state of the DNA (affects the ability of the DNA to interact with other molecules)
- Tighter winding (positive supercoil) reduces the chances of interaction
- Negative supercoiling (unwinding) increases access to proteins involved in replication or transcription
What is a genome?
genome is one complete copy of all the genetic information of an organism
How do genomes/ organization of genomes vary in Prokaryotes and Eukaryotes?
> Viruses & Prokarytoes have single or small number of linear/circular DNA/RNA molecules
Eukaryotes have nuclear genome and multiple DNA molecules (chromosomes). These include mitochondria & chloroplast genome whose DNA is a circular molecule
What are two ways DNA can be repeated?
-can be tandemly repeated or interspersed
-Tandem repeatsoccur inDNAwhen a pattern of
two or more nucleotides is repeated and the
repetitions are directly adjacent to each other
-Interspersed, repeated are scattered around genome
transposable elements (transposons, ‘jumping genes’)
What are the two types of interspersed Repeats?
LINE: Long Interspersed Nuclear Elements (6000-8000pb); these genes can move by themselves
SINE: Short Intersperse Nuclear Elements (<500bp) these genes rely on other elements like Alu sequences to move them
What are the two types of tandems repeats?
Micro satellites: repeats of sequences less than
about 2-6bpin length
Mini satellites: involve repeating of longer blocks
(10-60 bp)
Tandem repeats usually have a pattern of 2 or more nucleotides adjacent to each other
What is it called when the number of repeats in a tandem sequence is not known?
-called variable number tandem repeat or VNTR
What are the most common types of DNA in the human genome?
almost 44% is Interspersed repeated DNA
15% is tandem
1.5% is exons or expressed genes
What are the 3 possible was that DNA can be replicated? Which is observed?
- DNA can be replicated conservatively(make whole new strand), semi-conservatively (use other strand as template), or dispersive (bits of new (conservative) and old)
- semi-conservatively is seen, with each parent strand being the template for the new strand
What is the Messelson-Stahl experiment? What did they try and prove?
Wanted to prove semi conservative replication
-used radioactive isotope to tell the difference between old and new DNA
What they saw:
-grew e.coli in N14 medium as control; saw one band
-grew in N15 medium: saw one band
-took N15 and allowed to reproduce in N14; saw one band
-in N14, allowed cells to reproduce for a 2nd gen and saw two bands (one N14 14, one N15 14)
This proved semi conservative replication (had one old, and one new strand)
Who does circular DNA replication differ from other DNA rep? Who does this?
- Has single ORI
- has replication forks and proceeds bidirectionally with both strands being replicated
- theta replication (looks like theta symbol)
- Bacteria do this (replication is followed by binary fission)
