Structure of DNAGenes and Chromosomes

or

Cellular Reproduction pt. II

I. Deoxyribonucleic Acid• Serves as genetic

messenger• Master program that

controls metabolism (total of all chemical processes that occur in a cell)

II. Discovery of DNA

• 1869 Friedrich Miescher – Discovered DNA in pus from bandages

• 1910 T.H. Morgan – genes are on chromosomes

• 1927 HJ Muller – Induced mutation by Xrays

• 1944 Oswald Avery, Colin MacLeod, Maclyn McCarty – identified DNA as genetic material

• 1953 James Watson & Francis Crick, Maurice Wilkins & Rosalind Franklin – determined the structure of DNA http://www.nature.com/nature/dna50/watsoncrick.pdf

• 1973 Boyer and Cohen – cloned DNA with plasmid

• 1990 Launched Human Genome Project (see poster) projected finish in 2010, complete by 2003–http://www.ornl.gov/sci/techresources/Hu

man_Genome/home.shtml

DNA: Secret of Photo 51

NOVA film

III. Structure• Double stranded ladder, twisted to form a

helix, double helix• Sides are phosphates + sugar (phosphate

+ deoxyribose) –>– note the –ose ending, what does that tell us?

• Rungs of ‘ladder’ or steps are made of 2 nitrogen bases– Guanine ----Cytosine– Adenine ---- Thymine– Purines Pyrimidines

• Nucleotides – free floating “parts” are a sugar, phosphate and 1 base

IV. Replication• Building an exact copy before a cell

divides. Because the two strands are complementary, each strand serves as a template strand. After replication, you’ll have two identical strands.

• Semi-conservative replication: – each new strand keeps 1 of the 2 original

strands

A. Steps of replication1. Helicases (enzymes) separate the DNA

strand – they break apart the weak hydrogen bonds

2. Enzymes called DNA Polymerases add complementary nucleotides to each of the original strand.

3. DNA Polymerases are released and the two new identical strands result.

Replication fork – Y shaped region where DNA splits

B. Errors - mutations• 1. Positive- help

organisms adapt• 2. Neutral – no change• 3. Negative – kills the

organism

?

V. Codons• A group of three bases that code for a

specific amino acid• Triplet (codon) – the three letter ‘code’

word–20 different AA, Ex) G C U codes for

Alanine

What is a start code? Stop?

What is the protein made from: AUGCUCUGGGCAUAA

–A. Genetic code – • term used for the rules that relate how

a sequence of nitrogenous bases corresponds to a particular amino acid

–B. Anticodons –• three nucleotides of RNA that are

complementary to sequence of codon in mRNA

VI. Types of RNA• RNA: ribonucleic acid• 1. mRNA- messenger RNA carries the

genetic message from the nucleus to ribosomes in cytoplasm

• 2. rRNA- ribosomal RNA; part of the structure of ribosomes (made of mRNA and proteins)

• 3. tRNA- transfer RNA; transfers amino acids to the ribosomes to make a protein

VII. Protein Synthesis• A. Transcription- the process of

transferring DNA to RNA. Acts as a template for RNA synthesis.– 1. RNA Polymerase binds to gene’s promoter

(specific start sequence..AUG) and two strands of DNA unwind and separate.

– 2. Complementary RNA nucleotides are added and then joined (Uracil takes the place of Thymine)

– 3. RNA polymerase reaches the stop signal and DNA is released (zips back up) and new RNA is set free

• B. Translation – the process in which proteins are synthesized

• - proteins are made of polypeptides which are amino acids linked by peptide bonds. Sequence of amino acids determines how the polypeptides will twist and fold into 3-D structure of protein.

Translation continued

– 1. Ribosomal subunits tRNA and mRNA bind together over initializing codon.

– 2. Ribosomes move down the line with the tRNA attaching amino acids to form polypeptide chains

– 3. Stop codon reached and new polypeptide falls off. • Watch

Retrovirus

• Retrovirus: contain RNA instead of DNA and use this DNA to template new DNA using an enzyme called reverse transcriptase. Ex) HIV

DNA replication

• Watch an animation • Transcription and Tra

nslation

GENES AND HEREDITY WITH GREGOR MENDEL

Fundamentals of Genetics and Heredity

Why are my eyes blue?

Brother Gregor Mendel

• “Father” of modern genetics• Austrian monk, 1822 - 1884• Worked with pea plants in the monestary

garden• Followed some common traits in his pea

plants; plant height, flower position, pod color, pod appearance, seed texture, seed and flower color

Peas!

• 7 traits Mendel tracked

• Pollination: how plants breed (pollen from anthers to the stigma)– Self-pollination: same plants– Cross- pollination: two different plants (true

breeding = pure HH or hh)

– P generation: pure parent generation, self-pollinated

– F1 generation: 1st filial generation, offspring from P generation, crossed 2 purebred Ps

– F2 generation: 2nd filial generation, these are from self-pollinated F1 generation

What is the meaning of the term “gene” ?

• A gene is a segment of DNA located on a chromosome that codes for a specific hereditary trait.

• Ex) Tongue rolling, widows peak, eye color, freckles, PTC taster

• Molecular genetics: Study of structure and function of chromosomes and genes

• Recessive traits: ones that don’t show in the presence of a dominant trait

• Dominant trait: ones that show through,• Remember that our chromosomes are in

pairs? Mendel concluded that a pair of ‘factors’ controls each trait and each ‘factor’ came from a parent.

Allele is the letter we give to the gene / factor / trait

• Allele: Mendel’s ‘factors’, these are the alternate forms of a gene or trait (ex. blue or brown eyes) A or a, B or b…– Homogeneous: both alleles are alike– Heterogeneous: Alleles are different– Genotype: the genetic makeup of an

organism– Phenotype: physical appearance of organism

Comparative terms

• Phenotype –Physical appearance of organism

• Dominant – shows when present, with or without recessive trait

• Genotype- Genetic typing– Homozygous: same– Heterozygous: different

• Recessive- only shows w/out Dominant trait present

Mendel’s Laws of Heredity

• I. Concept of Unit Charachters– Inherited characteristics are controlled by

factors that occur in pairs.

• II. Principle of Dominance/Recessiveness– One factor (gene) in a pair may mask the other

preventing the other from having an effect

Mendel’s Laws of Heredity• III. Law of Segregation

– A pair of factors is segregated, or separated, during formation of gametes

• IV. Law of Independent Assortment– “Factors” or traits separate independently of

one another during gamete formation – *note the 4th law has been altered to include the fact

that genes on gene pairs (homologous chromosomes) are independently assorted to a gamete just as chromosomes are during meiosis.

Crossing Traits

• Probability: the number of times an event is expected to occur divided by the total number of times an event could happen. Ex. A 1 in 4 chance you will flip a coin and get heads.

• Or, just like your grades are figured: – 6,022 points / 8,023 points = 0.75 = 75%

• Monohybrid crosses – cross which only one characteristic is tracked. This is what we will focus on.

• Punnett Square is the device which we will use to follow those traits, they help predict the probability of offspring.

• Dominant traits are always capitalized and recessive traits are always lower case.

• Homo dom X Hetero• TT X Tt

Complete vs. Incomplete Dominance

• Complete dominance means the dominant trait completely dominates over the recessive ones if present. Ex) Rr and RR are both red

• Incomplete dominance just means they share phenotypic expression. Ex) RR is red, rr is white and Rr is pink!

• Codominance- neither allele is dominant but they are both expressed in offspring, Ex) blood types – AB+ or AB-

Spongebob Time

• Time for Spongebob Genetics Worksheets

• Practice the concepts of crossing traits and predicting the probability of offspring using these characters.

Dihybrid crosses• 2 characteristics are tracked, you have to

show each possible matchup in the cross.• TtBb X TtBb =

– TB, Tb, tB, tb, X TB, Tb, tB, tb• RRYY X rryy =

– Ry, Ry, rY, rY X rY, rY, Ry, Ry

– More complex, we can go further with a trihybrid cross!