Genetics Test 1- slide set 1
1850s – 1940s Genetics
- Started with Mendel and Darwin, something is inherited
– Comparing mutants with wild-type
Watson and Crick
-what is a gene
-described the structure of double-stranded DNA as a double helix.
- anti parallel (opposite polarity)
classical genetics, heredity, how genes and traits are transmitted from generation to generation
what genes are, the molecular structure and function of the genetic material, how genes are expressed; genomics
how traits are inherited that are determined by multiple genes
the distribution and behavior of genes in populations (usually one gene per trait)
mustard weed family
orange bread mold
strains can grow on minimal growth media and synthesize other organic molecules that are needed
mutants do not grow on minimal media and require supplements; specifically they need the molecule they cannot synthesize
-sugar is deoxyribose, bases are ACGT
- Nucleus, cytoplasm; Mitochondrion, chloroplast
- transcribed, producing RNA
- sugar is ribose, bases are ACGU
- Nucleus, cytoplasm; Mitochondrion, chloroplast
- reverse transcribed, producing DNA
– translated, producing a polypeptide
How is DNA expressed?
-Different genes – alleles
-Genotype + environment = phenotype
How DNA changes
– Experimental recombination
– Natural recombination; prokaryotes, eukaryotic meiosis
What is the monomer of DNA and RNA
Monomer = nucleotide
Structure of DNA
- Pentose sugar
- phosphate group PO4 2-
- Learn structures of ribose and deoxyribose
– 5’ carbon is outside of the ring
– OH = hydroxyl group
Phosphate group PO42 forms what type of bond and where?
– Forms phosphodiester bond between 3’ carbon of one sugar and 5’ carbon of the next
Polarity of the chain
is characterized by the phosphate group on a 5' carbon at one end and the hydroxyl group on the 3' carbon at the other end
- 9 member double ring
- 6 member single rings
What is base pairing?
The bonds between nitrogenous bases in the DNA double helix
Covalent bond between is where in the DNA sugar?
N and 1' carbon
-bases are 50% purines and 50% pyrimidines
- A+T/C+G may vary
What type of bonds are between G? +A/G, and how many are between the purines and pyrimidines?
- 3 bonds of C+G
-2 bonds A+T
bases are more inclined, helix wider, 11 base pairs per turn. Major (deep) groove is narrow and minor (shallow) is wide.
Distances above describe B-DNA, normal under hydrated conditions (although DNA in cells may be a little more twisted).
indicates zigzag sugar-phosphate backbone. Left-handed helix with 12 base pairs per turn. Unknown role.
Single-stranded RNA will fold up with secondary structure forming regions of double-stranded RNA separated by unpaired regions
What is the genome size?
Relative genome sizes of viruses, prokaryotes, and eukaryotes
Prokaryotes – 106 (or 1+ Mb)
Eukaryotes – most 108-109
Organization of DNA in viruses, prokaryotes, and eukaryoktes
prokaryotes- usually single circular chromosome, double-stranded DNA
eukaryotes- usually multiple linear
cleaves at the end
cleaves in the middle
lambda phage is double-stranded DNA single linear chromosme with single-stranded complementary ends
T2, T4, T6
double stranded DNA single linear chromosome
single-stranded DNA single circular chromosome
segmented single-stranded RNA
If multiple chromosomes, usually one main chromosome and others are smaller. If the smaller chromosomes are dispensable, they are called plasmids
multiple smaller chromosomes that are displensable
DNA is compacted because:
Positive and negative supercoiling – supercoiled vs. relaxed DNA controlled by topoisomerases (enzymes found in all organisms)
ends of looped regions are held in place so that each region can be supercoiled
-The number of chromosomes is characteristic of the species.
-Karyotype = complete set as in metaphase
- All eukaryotes have similarly structured chromatin
the stain-able material consisting of the DNA in a chromosome plus the proteins (about twice as much as DNA) complexed with it.
Histones and non histones
-histones are generally small and positively charged; about as much histone as DNA by weight
- nonhistones vary greatly at different stages of cell cycle, organism, and are negatively charged binding to histones
bead-like regions of DNA compacted by histone binding
When are chromosomes most compact?
during mitosis and meiosis, least compacted during S stage of interphase when replication occurs.
-important in cell division, these regions are where the mitotic or meiotic spindle fibers attach
-multiple proteins bind to these regions, forming the kinetochore where the end of the microtubule attaches
important in DNA replication, these regions are at the end of the chromosome and provide stability
telomere extreme ends
-contain a short repeated sequence that differs between species
- associated sequences can extend thousands of bp in from the ends
-Unique means that the haploid genome has a single copy or few copies of the sequence
-Usually genes regions (coding for proteins) are unique or repeat only a few times, but not all unique-sequence DNA is coding
-Highly (>105 copies)
-Unique: most of the genome
– Moderately repetitive: rRNA and tRNA (due to level of expression)
-55-60% of human genome is unique-sequence
– If repetitive sequences repeat many times in a row, they are called tandem repeats
(Some are long and associated with genes, like regions coding for tRNA and rRNA • Some are as short as 1-10 bp • Most common are in centromeres and telomeres)
Eukaryotic repetitive sequences
families of similar repetitive sequences may be spaced at irregular intervals (dispersed)
long interspersed elements 1-7 kb
short interspersed elements 100-400 bp
LINES and SINES in repetitive sequences
they make up a large part of the moderately repetitive sequences
full-length LINE-1 sequences
(represents about 15% of the mammalian genome)