Genetics Lecture Exam III

List the four criteria that the genetic material must meet.

• Store information → contain instructions for traits

• Be copied accurately → information must be passed to new cells/offspring

• Be expressed → information must be used to make traits/proteins

• Allow variation/mutation → must be able to change so evolution can occur

Analyze the results of (1) Griffith, (2) Avery, MacLeod, and McCarty, and (3) Hershey and Chase, and explain how they indicate that DNA is the genetic material.

• Griffith - worked with bacteria and tested different strains on mice, established the principle of transformation in bacteria

  • S type = smooth, harmful and kills mice

  • R type = rough, harmless and mice live

  • Heat-killed S = mice live

  • Heat-killed S + live R = mice die

  • something from the dead S bacteria transformed the R bacteria into harmful S bacteria, heritable transforming factor (but he didnt know what it was yet)

• Avery, Macleod, McCarty - asked what is Griffith’s transforming factor? destroyed different molecules from the S bacteria

  • Destroy protein → transformation still happens

  • Destroy RNA → transformation still happens

  • Destroy DNA → transformation stops

  • realized DNA causes transformation

• Henry & Chase - used bacteriophages

  • labeled DNA w radioactive P

  • labeled protein w radioactive S

  • after infection, DNA label entered bacteria while most protein stayed outside

  • realized DNA enters the cells and carries genetic information

Define nucleic acid.

• biological molecule that stores and/or helps use genetic information

  • DNA

  • RNA

Describe the four levels of complexity of DNA.

• nucleotide

  • individual building block

• DNA strand

  • nucleotides connected together

• double helix

  • two DNA strands paired together

• chromosome

  • DNA packaged and organized with proteins

Describe the structure of a nucleotide.

• 3 parts

  • phosphate group

  • 5-carbon sugar

  • nitrogenous base

Compare and contrast the structures of nucleotides found in DNA and in RNA.

• DNA

  • deoxyribose sugar

  • A,T,G,C

  • uses thymine

  • usually double-stranded

• RNA

  • ribose sugar

  • A,U,G,C

  • uses uracil

  • usually single-stranded

Describe the structural features of a DNA strand.

• sugar-phosphate backbone

  • sugars and phosphates connect to form the outside of the strand

• nitrogenous bases point inward

  • bases are available to pair with bases on the other strand

• phosphodiester bonds

  • connect nucleotides together along the backbone

• 5’ and 3’ ends

  • DNA has directionality

Outline the key experiments that led to the discovery of the DNA double helix.

• Chargaff

  • discovered equal amounts of A = T and C = G

  • suggests bases pair in specific ways

• Franklin and Wilkins

  • used Xray crystallography/diffraction to study DNA

  • found that DNA has a helical structure, consistent width, and repeating structural features (photo 51)

• Watson and Crick

  • used available evidence to build 3D model of DNA

  • proposed double helix structure in 1953

Outline the key structural features of the DNA double helix.

• antiparallel

  • strands run in opposite directions

  • 5’ to 3’ & 3’ to 5’

• complementary base pairing

  • A pairs with T

  • G pairs with C

• hydrogen bonds

  • A-T = 2 hydrogen bonds

  • G-C = 3 hydrogen bonds

• sugar-phosphate backbone

  • backbone is on the outside

• bases inside

  • based point towards the center and pair w the opposite strand

• double helix

  • two strands twist around each other

Outline the key structural features of RNA.

• generally single-stranded

  • ribose sugar

  • phosphate

  • A,U,G,C

  • uracil instead of thymine

• can fold back on itself and form structures through base pairing

• major RNA types

  • mRNA = carries genetic instructions

  • tRNA = brings amino acids

  • rRNA = helps form ribosomes

Describe the general organization of functional sites along bacterial and archaeal chromosomes

• most bacteria and archaea have one main circular chromosome (some exceptions)

• chromosome contains functional regions

  • genes - instructions for making RNA or proteins

  • promoters - DNA sequences where transcription begins

  • operons - groups of genes controlled by one promoter and transcribed together

  • origin of replication - where DNA replication begins

  • termination region - where replication ends

Outline the processes that make a prokaryotic chromosome more compact.

• supercoiling - DNA twists around itself, making it more compact

• DNA-binding proteins - proteins bend, wrap, or organize DNA

• loop formation - DNA forms loops that help organize the chromosomes

Describe the variation in size of eukaryotic genomes.

• eukaryotic genome sizes vary greatly between species

• some organisms have relatively small genomes

• others have enormous genomes

• genome size does not necessarily predict organism complexity

  • genome size depends partly on the amount of repetitive DNA and other noncoding sequences, not just the number of genes

Define repetitive sequence, and explain how this type of sequence affects genome sizes.

• repetitive sequence = DNA sequence found many times in a genome

• types include

  • tandem repeats - sequences repeated right next to each other

  • interspersed repeats - repeated sequences scattered throughout the genome, often because of transposable elements

• repetitive DNA can make genomes much larger without adding more protein-coding genes

Summarize the studies of McClintock, and explain how they revealed the existence of transposable elements.

• she studied corn

Describe the organization of sequences within different types of transposable elements.

Explain how transposons and retrotransposons move to new locations in a genome.

Discuss the effects of transposable elements on gene function.

Define chromatin.

Describe the structures of (1) nucleosomes, (2) nucleosome interactions according to the zigzag model, and (3) loop domains.

Compare and contrast euchromatin and heterochromatin, and distinguish between constitutive heterochromatin and facultative heterochromatin.

Explain the meaning of chromosome territory.

List the four levels of chromosome structure in a nondividing cell.

Describe the levels of compaction that lead to a metaphase chromosome