Chapters 1 and 2 Flashcards by Holly Harrison

How do geneticists gain insight on specific processes?

Isolating mutants and comparing them with normal strains

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Modern genetics research focuses? (6)

Heredity in populations
Evolutionary processes
Genes that control steps in processes
Mapping genes (location on chromosome)
Products of genes (Enzymes, RNA)
Molecular features of genes  and regulation of gene expression (epigenetics, promoters, operons)

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Gene

Basic unit of inheritance

Controls one or more characteristics; encodes proteins/functional RNA

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Alleles

Alternative forms of a gene

Most have one wild type and one or more mutant alleles

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Wild Type (WT)

Standard form of a gene; usually most commonly occurring natural variant.
Denoted by +

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Mutant

Form different from wild type

Denoted by -

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Genotype

Genetic makeup of an organism

Usually lists only mutant alleles

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Phenotype

Observable properties of an organism

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Prokaryotes, eukaryotes, viruses: Which have DNA/RNA?

Prokaryote and eukaryote: DNA

Viruses: DNA or RNA in protein coat

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Eukaryotes

and examples

Genetic material enclosed in a nucleus (True nut)
Plants, animals, fungi
Have multiple linear DNA in nucleus (23 pairs in humans) and one circular DNA in organelles
Uni or multicellular

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Prokaryotes

and example

Have no nuclei
Bacteria
Has one circular DNA in cytoplasm
Almost always unicellular

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Desirable qualities for research organisms

Well-known genetic history
Short life cycle
Large number of offspring
Ease of growing and handling
Marked genetic variation within population

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1 eukaryote used in genetic research (latin and common name)

Mus musculus (mouse)

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1 Prokaryote used in genetic research (latin and common name)

Escherichia coli (intestinal bacterium)

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What did scientists originally believe was the genetic material? Why?

Protein; Because they have a greater capacity for storing information (20 AAs vs 4 nucleotides)

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Griffith’s transformation experiment

1928
With streptococcus pneumonia bacteria in mice, showed genetic material passed from dead bacteria into living ones, allowing them to change their cell surface
Discovered a “transforming principle” but didnt know what it was or how it worked

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S vs R strain

S: smooth surface that fools WBCs by hiding antigens; infectious
R: rough; not infectious

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S strain heat killed:

Not infectious

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S strain (heat killed) + R strain=

Infectious

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Transforming principle

Unknown mechanism that causes R bacteria to uptake genetic material from dead S bacteria and transform into an infectious strain

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Avery’s Transformation Experiment

To determine identity of transforming principle
Lysed dead S cells with detergent, separated cell extract from cell debris by centrifuge to determine component of extract transforming
Added DNase (destroys DNA) and no transformation
Transforming principle is DNA
Many thought enzymes were contaminated

Hershey-Chase Bacteriophage experiments

Labeled T2 DNA with 32P and T2 proteins with 35S and each group mixed separately with E.coli
32P DNA found inside host (genetic material)
35S protein found outside host

3 Parts of a nucleotide

Pentose Sugar
Nitrogenous Base
Phosphate group

Difference between DNA and RNA

At 2’, DNA has H and RNA has OH

Purine

Double ring Nine-membered Adenine and Guanine

Pyrimidine

One ring 6 membered Cytosine, Thymine, and Uracil

How are bases attached to pentose sugar?

Covalent bond between Nitrogen in base and 1' carbon of sugar

Nucleoside

Sugar-base combo | Without phosphate

Where is phosphate of nucleotide added?

5' carbon of sugar

How are sugar and phosphate groups attached?

Stable covalent bonds (phosphodiester bonds) between phosphate group on 5'C of one nucleotide and 3' C of another Asymmetry of phosphodiester bonds creates 5' to 3' polarity

Watson and Crick

DNA has 2 polynucleotide chains would around each other in a right-handed double helix Chains are antiparallel Sugar-phosphate backbone on outside, bases on inside Bases held together by Hydrogen bonds between complimentary bases

Erwin Chargaff

Showed amount of G=C and A=T (Chargaff's rules) DNA composition varies among species, but rule is same Suggested paring of DNA but Chargaff didn't realize

Rosalind Franklin and Maurice Wilkins

X ray diffraction images of DNA showed helical structure with regularities along axis of molecule

Length between base pairs

.34 nm

Length of one helical turn

3.4 nm

How many base pairs in one complete turn?

External diameter of dsDNA

2 nm

Minor and Major groove of DNA results from

Way bases H-bond with each other, opposite backbones not equally spaced

Where does double-stranded RNA exist?

In some bacteria genomes | Usually single stranded

Virus nucleic acid

Can be dsDNA, ssDNA, dsRNA, or ssRNA Linear or circular Single molecule or several segments

Bacteriophage nucleic acid

one short ssDNA | Chromosome resistant to exonucleases, circular

Typical prokaryotic genome

One circular dsDNA chromosome Plasmids possibly Unique-sequence DNA with repeats of only rRNAs and tRNAs

Eukarotic genome

Diploid chromosomes (2 genomes) Have mix of unique and repetitive DNA Repetitive derived from transposable elements Have chromatin

Transposable elements

Jumping DNA | About 40% of human genome

Genome

Information in one complete haploid chromosome set

C value

Total amount of DNA in the haploid genome of a species

C-value paradox

The structural complexity and C-value of an organism are not related

Chromatin

DNA protein complex that constitutes chromosomes | Euchromatin and Heterochromatin

Nucleosome

Basic unit of chromatin Histone core+ core DNA Joined by linker DNA and Histone H1

Euchromatin

Transcriptionally active Lightly packed Most of genome

Heterochromatin

Usually transcriptionally inactive Tightly packed Centromeres and Telomeres

Which 3 experiments all focused on discovering DNA as genetic material?

Griffith Avery Hershey-Chase