biology 12-17

1. Briefly describe the structure of DNA. 

DNA: deoxyribonucleic acid; the genetic material of all living organisms; 

DNA as a double helix:  

• Double-stranded polymer of nucleotides; nucleotide made of a sugar, a nitrogen-containing base, and a phosphate group; 

• 4 different nitrogen-containing bases in DNA: adenine (A), cytosine (C), guanine (G), and thymine (T) 

• Sugar and phosphates on outside; bases paired up in middle 

2. Briefly describe the steps in the process of DNA replication. 

- DNA replication; copying the DNA molecule; DNA strands separate; enzyme DNA polymerase uses each old strand as a template to build new second strand; new strands built one nucleotide at a time based on complementary base pairing; 

3. Briefly describe the steps in transcription and translation that produce proteins. 

 Transcription; making RNA from DNA template 

• Two strands of DNA separate; RNA polymerase binds DNA at promoter region and adds nucleotides one at a time (according to complementary base pairing) to build a strand of mRNA; 

Translation; making a protein based on codon sequence of mRNA; takes place on ribosomes; ribosome reads codon sequence of mRNA; transfer RNA (tRNA) brings amino acids to ribosomes one at a time and ribosome binds them into a chain; tRNA has anticodon that is complementary to codon on mRNA to determine which amino acid is added; translation starts at start codon and ends at a stop codon; 

4. What is the start codon for translation? List the stop codons for translation. 

 AUG is starting codon; UAA, UAG, UGA are stop codons 

1. Briefly describe the difference between heterochromatin and euchromatin. 

•  euchromatin is more loosely packed and is available for transcription 

•  heterochromatin is more tightly packed and is considered inactive; 

2. Briefly describe the difference between transcription factors and transcription activators. 

• transcription factors help RNA polymerase bind DNA at promoter region leading to more transcription;  

• transcription activators bind DNA at enhancer regions and also lead to more transcription;  

absence of these factors leads to less transcription 

3. Briefly describe the various ways in which eukaryotes control gene expression. 

 Eukaryotes have several mechanisms  

• Transcriptional control; transcription factors help RNA polymerase bind DNA at promoter region leading to more transcription; transcription activators bind DNA at enhancer regions and also lead to more transcription; absence of these factors leads to less transcription; 

• Posttranscriptional control; mRNA processing; includes removing introns and splicing exons back together; includes alternative splicing where exons are spliced together in different arrangements; includes RNA interference which destroys RNA molecule before translation 

• Translational control; presence or absence of 5’cap and length of poly-A tail on mRNA can determine whether translation takes place 

• Posttranslational control; mechanisms in cell get rid of old, unused, or incorrectly folded proteins; 

1. Define a clone. 

- Clone: exact genetic copy of a gene, cell, or organism 

2. Briefly describe how a restriction enzyme works, including its function in bacteria. 

 - Restriction enzyme: made by bacteria to cut up foreign DNA; cuts DNA at recognition sequence 

3. Briefly describe the steps in the process of DNA fingerprinting, including using PCR to obtain DNA and analyzing STRs. 

- DNA fingerprinting: use PCR to make many copies of short tandem repeats (STRs) and compare DNA from two different sources to see if they have the same number of repeats 

4. Briefly describe the steps in the procedure for cloning a gene. 

Cloning human gene: cut chromosome and plasmid with same restriction enzyme; this creates “sticky ends”; place two pieces of DNA in same tube and they stick together because of complimentary base pairing; put recombinant plasmid into bacteria; bacteria make protein gene codes for DNA sequencing. Procedure used to determine the order of nucleotides in a DNA segment; it’s automated now.  

Define evolution 

•  Evolution- the change in the gene pool of populations over time 

 2. List the components of the Theory of Evolution Through Natural Selection. 

• Organisms exhibit variation that can be passed from one generation to the next: inheritable variation; Darwin did not know about chromosomes and meiosis, so he had no mechanism for this 

• Organisms compete for available resources: Darwin applied Malthus’ proposal to all organisms, not just humans 

• Individuals within a population differ in terms of their reproductive success: fitness is the reproductive success of an individual relative to the other members of a population; the most fit individuals are the ones that capture a larger amount of resources and convert these resources into a larger number of viable offspring; fitness is influenced by different factors for different populations 

• Organisms become adapted to conditions as the environment changes: differential reproduction generation after generation causes adaptive traits to increase in frequency in each succeeding generation 

3. Briefly describe the different types of evidence for Evolution. 

- Fossils- show animals that resemble animals of today but are not the same; show animals that resemble extinct animals as well as animals that live today (transitional fossils) 

- Biogeographical evidence- geography separates continents, and you have a different mix of organisms 

- Anatomical evidence- homologous structures have similar structure due to common ancestor; vestigial structures present in two different groups, functional in one, useless in other 

- Biochemical evidence- every organism uses DNA, uses same genetic code, and uses ATP; every organism that has electron transport chain has cytochrome c gene; can compare amino acid sequences of different species and see similarity 

- Developmental biology- hox genes control development of embryo; hox genes in every animal; different number and types in different animals, but all have them 

1. Define the following 

• Population: a group of organisms of a single species living together in the same geographical area; all members of a species in a given geographical area 

• Microevolution: the change in allele frequencies in a population over time  

• Gene pool: all the alleles of all the genes in all the individuals in a population   

2. Briefly describe the factors that can change allele frequencies in a population. 

 Allele frequency: the percentage of each allele in a population’s gene pool 

Hardy-Weinberg principle; the allele frequencies in a population will change if the following conditions are met: 

1. mutation 

2. imigration 

3. small gene pool 

4. Non- random mating 

5. Selection 

3. Briefly describe the modes of natural selection. 

• Stabilizing: favors average over either extreme 

• Directional: favors one extreme over average and other extreme 

• Disruptive: favors either extreme over average 

1. Define biological species. 

• Biological species is a group of organisms that successfully reproduce (interbreed) 

2. Briefly describe the reproductive isolation mechanisms that prevent two groups from interbreeding. 

• Habitat isolation: species at same locale occupy different habitat 

• Temporal isolation: species reproduce at different times 

• Behavioral isolation: courtship behaviors make them unattracted to each other 

• Mechanical isolation: genitals don’t match 

• Gamete isolation: sperm cannot fertilize the egg 

• Zygote mortality: zygote (product of sperm fertilizing egg) does not survive 

• Hybrid sterility: offspring is sterile 

• F2 fitness: second generation does not survive or is sterile 

3. Define the following: 

1. Speciation- the splitting of one species into two or more species 

2. Allopatric speciation- populations separated by geographic barrier; evolve into separate species 

3. Sympatric speciation- populations not separated by geographic barrier; evolve into separate species 

4. Adaptive radiation- one species gives rise to several new species when introduced to a new environment