BIO 1070 CHAPTER 10

lecture 22 and 23

DNA

• deoxyribonucleic acid; the genetic material

• stores info in a specific sequence in which four nucleotides are arranged.

• The human genome is 3.2 billion nucleotides long

• base pairs : Guanine and Cytosine, Adenine and Thymine

Amino acids

the 20 building blocks used to make proteins

RNA polymerase

the enzyme responsible for making RNA copies of DNA templates

ribosomes

the enzyme responsible for converting the information in RNA molecules into the amino acid sequence of proteins

transcription

• the copying of DNA sequences into RNA sequences

• information in double stranded DNA is transcribed into single stranded RNA

• DNA is unwound forming a transcription bubble. An enzyme, RNA polymerase, starts transcription at a promoter and uses the information on one DNA strand as a template.

translation/ protein synthesis

• the synthesis of proteins by ribosomes

• Translation begins when a tRNA anticodon recognizes a codon on the mRNA

• the large ribosomal subunit joins the small subunit, and a second tRNA is recruited.

• As the mRNA moves relative to the ribosome, the polypeptide chain is formed

• entry of a release factor into the A site terminates translation and the components dissociate.

• Combinations of the four nucleotides in RNA are translated into the 20 different amino acids

• involves decoding an mRNA message into a polypeptide product

How many amino acids can we make organically?

We can make 7 amino acids

The other 13 we need have to come through supplementation

RNA

• ribonucleic acid

• carries instructions copied from DNA

• needed for transcription process

• typically a single stranded molecule

• has a hydroxyl group at the 2’ carbon

What are the differences between DNA and RNA?

• RNA is double stranded

• RNA uses U (Uracil) instead of T(Thymine)

• The names correspond to an attached OH bond

• Ribo nucleic- OH bond

• Deoxyribo - no OH bond

Amino acids

• translation takes info stored from nucleotides and turns them into amino acids

• every kind of protein has a different sequence of amino acids- but the same kinds do

• the side chains are what makes amino acids different

• Proteins are made from 20 different amino acids

The central dogma

• genetic material flows from DNA to RNA to protein

• DNA ——> RNA———>PROTEIN

• DNA is transcribed into mRNA and carries the information necessary for protein synthesis

codon

• a three nucleotide sequence ex: UAG

The genetic code

• AUG is reserved for use as a start codon.

• UAA, UAG, and UGA are the three stop codons

• 61 of the possible 64 triplet codons code for specific amino acids

• Some codons are synonymous (code for the same amino acid) there is a redundancy in the genetic code

• Many changes to codons are conservative (don’t change the amino acid found in the protein)

Point mutations (substitutions)

• silent mutation

• nonsense mutation

• missense mutation

silent mutation

a change at the DNA level that does not change the amino acid sequence of a protein

nonsense mutation

a change at the DNA level that introduces a stop codon

missense mutation

tend to be conservative

Frameshift mutations

• adding or deleting nucleotides in anything but multiples of three disrupts the reading frame of a gene

• all downstream amino acids are usually changes as a result

• the frequency of frameshift mutations is about 1/10 that of point mutations

sicke cell anemia

• instead of 2 glutamic acids in a DNA sequence, people with sickle cell have a valine and a glutamic acid .

• unrelated individuals are 99.5% identical at the level of their DNA sequence.

• This particular sequential difference is why sickle cell happens.

The genetic code

• the universality of the genetic code makes it possible to make transgenic organisms where a protein from one organism is made by another.

transgenic organisms

• the protein from one organism is put into another organism

• this process is harder for vertebrae than plants

• spider goats and insulin cows are very popular

Spider goats

• gene coding for spider silk protein isolated from spiders

• placed downstream of a promoter associated with a protein that is only expressed by goat mammary tissues

• placed into fertilized goat eggs

• creation of a herd of true-breeding goats that produce spider silk protein in their milk

• proteins can be stronger than material in a bullet proof vest

• can be helpful for military but production would be too time consuming

• because of this, goats are used

insulin cows

• gene coding for human insulin isolated

• placed downstream of a promoter associated with a protein that is only expressed by cow mammary tissues

• placed into fertilized cow eggs

• creation of a herd of true- breeding cows that produce human insulin in their milk

glyphosate

• making plants glyphosate - resistant can kill off any plants w/o the glyphosate ( effective for farming, especially 90% of corn and soybean farms)

• transgenic glyphosate - resistant plants have been commercially available since 1995

tRNA structure

• RNA is usually thought of as a single stranded molecule but it, like DNA, is capable of intra- and inter-molecular base pairing.

• In biology, structure and function are usually inter - related

Cloning

• making many copies of a sample of information

• can clone an entire organism

• take the least differentiated cells and take the nucleus out

• then put that nucleus in a new organism

characteristic

a heritable feature (like flower or seed color)

trait

a recognizable variant of an inherited characteristic

genes

instructions (at the level of DNA) for a characteristic that are passed individually to offspring

alleles

recognizably different variants of a gene that determine a particular trait for a characteristic

phenotype

observable traits expressed by an organism

genotype

the underlying genetic makeup, consisting of both physically visible and non-expressed alleles

homozygous

an individual carrying identical alleles for a gene (PP or pp)

heterozygous

an individual carrying two different alleles for a gene (Pp)

• The dominant allele is often capitalized (P)

• the recessive allele is often lower case (p)

Peas as a model genetic organism

• peas naturally self fertilize

• flower petals remain tightly sealed until pollination is complete

• this results in “true breeding “ pea plants

• no unexpected traits in offspring

• short generation times

• large progeny

• no ethical constraints on mating experiments

Menel’s experiments

• performed hybridizations

• studied 7 characteristics with recognizably different traits

hybridizations

mating two true-breeding individuals that have different traits

Mendel’s first mating experiment

• mated two contrasting, true breeding varieties

• True breeding parents are called the P generation

• Offspring of the P generation is called the F^1 generation

• When the F^1 generation self- pollinate, the F² generation is produced

P generation

parental generation in Mendel’s experiment

F^1 generation

the hybrid offspring of the P generation

F² generation

progeny of the self hybridization of the F^1 generation

Mendel’s conclusions

• When Mendel crossed purple flowers with white, all the offspring were purple ( F1 generation)

• Mendel concluded that characteristics could be divided into expressed and latent traits (dominant and recessive)

• dominant traits are those that are inherited unchanged in a hybridization

• recessive traits become latent, or invisible(but unchanged) in the offspring of a hybridization

Law of dominance

• for each characteristic an organism inherits two alleles, one from each parent

• in a heterozygote, one trait will conceal the presence of another trait for the same characteristic- law of dominance

• the dominant allele determines the organism’s appearance

Pedigree analyses

• humans are not good organisms for genetic modeling

• human geneticists usually need to rely on analyses of inheritance in naturally occurring families

• in pedigrees, circles represent females, squares represent males, and filled symbols afflicted individuals

What are the genotypes of the individuals labeled 1 and 2?

individual 1 - homozygous recessive

Individual 2- heterozygous dominant

If these were pea plants, how would you determine the genotype of this female ?

punnet square

Abraham Lincoln / MEN2B

• may have had an autosomal dominant disorder

• wife did not have the disease

• 50% chance son had it

sex- linked trais

• traits (genes) located on the sex chromosomes

• sex chromosomes are X and Y

• XX genotypes for females

• XY genotype for males

• many sex linked traits are carried on the X chromosome

Common sex- linked traits

• red-green color blindness

• hemophilia

• high blood pressure genes

Karyotyping/cytogenetics

• karyotype- a picture of an individual’s chromosomes arranged by length

• can be used to diagnose genetic disorders- especially those involving chromosomal abnormalities

• 22 pairs of autosomes

• 1 pair of a sex chromosome

nature vs nurture

• studies of identical twins reveal that much of what we think is important about ourselves is inherited

• environment can exert a heavy influence as well

epigenetics

• the study of heritable changes that are not due to changes in DNA sequences

• your grandmother’s experiences can cause you to express your genes differently

• addiction, anxiety, depression, and fear conditioning can be influenced epigenetically