BIO Exam 3

In the supernatant of the centrifuged media, did Hershey and Chase find P-32 or S-35?

S-35

In the pellet of the centrifuged media, did Hershey and Chase find P-32 or S-35?

P-32

What could Hershey and Chase conclude from their experiment?

Bacteriophage transferred DNA and not proteins to bacteria. Therefore, DNA is the genetic material

________ made uniformly oriented DNA fibers that were used to obtain X-ray diffraction

images of DNA, ______ realized that purines bond with pyrimidines, and _______ realized that

sugar-phosphate formed the DNA backbone.

Maurice Wilkins, James Watson and Francis Crick, Rosalind Franklin

The semiconservative nature of DNA replication states that only one of the parental DNA strands is replicated. True or false?

false

What are the functional restrictions of DNA polymerase?

• They can only copy single-stranded DNA

• They rely on an RNA primer to start synthesis of the daughter strand

• They can only add nucleotides to the 3’ end

What are the steps for telomere extension by telomerase?

1. RNA primer removal following lagging strand synthesis creates 3’ overhang.

2. The telomerase’s RNA template binds to the 3’ overhang.

3. Telomerase RNA acts as a template for addition of DNA nucleotides to 3’ overhang.

4. Telomerase and its RNA template shift, elongating 5’-3’ DNA strand.

5. DNA polymerase elongates the 3’-5’ strand through addition of nucleotides.

DNA polymerase 1

Fills gaps that arise during replication/repair

DNA polymerase 2

Undertakes proofreading and repair/editing

DNA polymerase 3

Undertakes regular DNA synthesis

What are three reasons why the cell tolerates a higher level of transcription errors vs. replication errors?

1. Many RNAs are only a few thousand bp long & may have no or 1 error

2. RNA errors are not passed to next generation of cells

3. RNA has a short lifespan

RNA polymerase

adds complimentary nucleotides in 5’-3’ direction

promoter

sets the start site for transcription

transcription unit

is the DNA sequence being transcribed

transcription factor

regulates initiation of transcription

A DNA sequence is 3’- ATGCGTCA - 5’. What is the sequence of the RNA that is transcribed from this strand? What is the sequence of the template and coding strand?

• RNA sequence: 5’ – UACGCAGU – 3’

• Template strand sequence: 3’- ATGCGTCA - 5’

• Coding strand sequence: 5’ – TACGCAGT – 3’

Why do eukaryotic mRNAs undergo?

1. addition of 5’-cap: to protect the 5’-phosphate groups of RNA from enzyme degradation in the cytosol (1 point; partial credit if not all information is present).

2. addition of 3’-tail: makes RNA more stable and helps it get transported from nucleus to cytosol (1 point; partial credit if not all information is present).

3. splicing: removes introns that are commonly found in eukaryotic genes and mRNA (1 point; partial credit if not all information is present).

Why do prokaryotic mRNAs not undergo?

1. addition of 5’-cap: prokaryotes undergo simultaneous transcription and translation and therefore enzymes often cannot break their RNA before translation

2. addition of 3’-tail: prokaryotic RNA is already in the cytosol and does not need transportation

3. splicing: prokaryotic RNA very rarely contains introns

During transcription, which enzyme is responsible for unwinding the dsDNA?

RNA polymerase

Synonymous mutation

results in unaltered amino acids

Nonsense mutation

results in premature termination of translation

Loss-of-stop mutation

results in late termination of translation

Missense mutation

results in a single amino acid change

Frameshift mutation

results from insertion/deletion of nucleotides

What are the steps for translation initiation and termination?

1. The small ribosomal unit binds to mRNA at the 5’ end.

2. Methionine-charged tRNA binds to AUG codon

3. The large ribosomal subunit joins the initiation complex

4. The translation elongation steps occur.

5. At the A ribosomal site, a release factor binds to the stop codon.

6. The release factor disconnects the polypeptide chain from tRNA molecule.

What are the steps for translation elongation?

1. At the A site, the anticodon of incoming tRNA binds to mRNA codon.

2. The peptidyl transferase enzyme adds methionine attached to tRNA in P site to the amino acid attached to tRNA in A site.

3. The ribosome shifts down one codon, moving the uncharged tRNA to E site and the tRNA carrying the two amino acids to P site.

4. A newly charged tRNA enters A site, releasing uncharged tRNA from E site.

5. The process continues until a stop codon reaches the A site.

In which organelle can already initiated protein translation continue?

Rough ER or rough endoplasmic reticulum

What are the functions of rRNA?

• Ensures proper alignment of tRNA anticodon and mRNA codon

• It breaks bond between amino acid and tRNA

• formation of bond between two amino acids

genetics

study of heredity

heredity

process of passing traits from parents to offspring

hereditary

describes traits/conditions that are passed down

Who was Mendel?

set the framework for genetics long before chromosomes/genes had been identified

mendelian genetics

traits are inherited through genes that parents pass to their offspring

Mendel’s model system

• pea plants: powerful system for studying heredity

• controlled mating

• short generation time

• large number of offspring

• easy to grow and maintain

monohybrid crosses

crossing 2 individuals/organisms that consistently produce offspring with same trait as themselves that differ in a single trait

P0

plants used in first generation crosses (parental)

F1

offspring of P0

F2

offspring of F1

phenotype

observable trait/physical expression of those genes

genotype

genetic makeup of an organism

homozygous dominant and heterozygous are what?

identical

punnet square

diagram used to predict the possible genetic outcomes of a cross between 2 individuals

What are Mendel’s laws?

1. Law of segregation: each organism has 2 alleles for a trait; alleles separate for gamete formation

2. Law of Independent Assortment: genes for different traits are inherited independently; don’t affect one another

3. Law of dominance: some alleles are dominant and mask recessive alleles; dominant > shows phenotype recessive > shows both alleles are recessive

Why are Mendel’s laws significant?

• traits are inherited as genes rather than blending together

• established predictable patterns of inheritance

• introduced ideas of genes from parents

• biology more quantitative and experimental

test cross

cross between individual with unknown genotype and a homozygous recessive individual to determine the unknown genotype

pedigree analysis

method used to track how traits/genetics conditions are inherited within a family across generations

Expectation of law of dominance

incomplete dominance; codominance

Expectation of law of independent assortment

linked genes; epistasis

Expectation of law of segregation

multiple alleles; sex-linked traits; recessive lethal allele

incomplete dominance

neither allele is completely dominant over the other

codominance

both alleles are fully and equally expressed in an heterozygous individual

linked genes

genes close together on same chromosomes are inherited together; violates law of independent assortment

epistasis

1 gene modifies another gene’s expression at a different locus; genes don’t always act independently

sex-linked traits

different inheritance patterns in males and females

recessive lethal allele

causes death when individual has 2 copies of it, but has little/no effect when 1 copy is present

fertilization

chromosome from each parent

nondisjunction

chromosomes/sister chromatids don’t separate properly during cell division

euploidy

appropriate number of chromosomes; 22 pairs of autosomes and 1 pair of sex chromosome

aneuploidy

abnormal chromosome number

monosomy

losing 1 chromosome

trisomy

gaining 1 chromosome

polyploidy

more than 2 sets of chromosomes; common in plants

chromosomal inversion

segment of chromosome breaks off, flips around, and reattaches in reverse orientation

chromosomal translocation

segment of chromosome breaks off and attaches to another chromosome

genetic material

• must store info for cell to carry out functions and be able to replicate itself

• most scientists believed it was proteins

• experiments showed it was DNA

griffith experiment

• conducted with 2 stains of streptococcus pneumoniae

• R converted to S cells

• something passed from nonliving to living cells

avery experiment

• identifying what caused the transformation of R to S cells

• only DNase treatment which was the loss of transforming activity

hershey and chase experiment

• used bacteriophages by transferring their genetic material

• radioactive isotopes used to tag specific macromolecules

• DNA is tranfserred by bacteria

32P

labels nucleic acids

35S

labels proteins

What happened in 1952?

DNA composition and arrangement of nucleotides was known

Aform DNA

makes better crystals; most people focused on it

Bform DNA

helical; sugar-phosphate backbone had to be on the outside

central dogma of biology

describes how genetic info flows in a cell

prokaryotic chromosome

single ORI

eukaryotic chromosome

many ORI

helicase

unzips DNA helix at replication fork by breaking hydrogen bonds between strands

topoismerase

causes single-strand breaks that allows the DNA to unwind the supercoil strain from helicase activity

ligase

seals other nicks made during replication primase is replaced with DNA

DNA polymerases

• regular synthesis

• proofreading, repair/editing

• removes RNA primer and fills gap with DNA

• works with primase to start replication

Double Helical DNA synthesis

2 strands of double helix are antiparallel

continuous synthesis of leading strand when complementary nucleotides are added in an antiparallel direction, extending from primer’s 3’ end

DNA synthesis problem

DNA polymerase cannot add nucleotides onto a free 5; end and elongate in 5’ direction

DNA synthesis solution

lagging DNA strand is synthesized discontinuously as short fragments

okazaki fragments

short segments of DNA synthesized on lagging strand

leading strand

synthesized continuously; copied all the way to the end

lagging strand

synthesized discontinuously; is not copied all the way to the end

end replication problem

shortening of DNA with every cell division

telomeres

short repeating DNA sequences; on DNA ends; added constantly to prevent loss of genes

telomerase

enzyme that adds telomeres; active only in germ and certain