Unit 6 Flashcards
In the early 1900’s what two things did scientists decide chromosomes were made of?
-DNA and protein
Originally, what molecule did scientists think was the hereditary material in the nucleus? Why?
-protein because it was more complex and built of many more amino acids (dna-4 and protein 20)
Explain Fredrick Griffith’s transformation experiment in 1928.
Griffing heat killed S cells and mixed them with living R cells that caused the mouse to die. Something in this mix was being transferred to the R cells to kill the mouse. Independently the R cells and the heat killed S cells did not kill the mouse but the alive S cells did.
In 1944, Avery, McCarty and McLeod announced the transforming factor in Griffith’s experiment was _________.
DNA
Hershey and Chase worked with bacteriophages. What is a bacteriophage? What were they testing in their experiment?
Bacteriophages are viruses that infect bacteria
-They were testing that DNA is the genetic material of a phage(bacteriophage)
(whether phages work by transmitting their DNA or protein)
Why was it important the DNA was tagged with phosphorus and the protein was tagged with sulfur?
DNA has phosphorus and does not have sulfur
Protein has sulfur but not phosphorus
What were Erwin Chargaff’s findings? Why were his findings significant in the structure of DNA?
- purines and pyramids go together
- percentage of Adenine equal to thymine (A and T are equal) (C and G are equal)
- DNA composition varies from one species to the next
What is Rosalind Franklin known for? How was this significant to the structure of DNA?
produced a picture of the DNA molecule with X-ray crystallography. She found that a DNA has the shape of double helix (helical) Made of two strands
-the width of strands (help figure out that A goes with T and so on)
Who built the first model of DNA? What ideas from other scientists (name at least two) led them to be certain of which nitrogenous bases are bonded together.
Watson and Crick
-the width of bases and
What is the type of bond that holds the nitrogenous bases together? Why Is it important that this type of bonding mechanism is used in DNA?
Hydrogen bond
-They are weak so they break easily allowing for new dna to be build
What is meant by the “semiconservative model” of DNA replication?
Half new half old dna
What 3 things comprise a nucleotide? What molecules make up the backbone of DNA?
nitrogenous base,-phosphate group, and deoxyribose sugar,
-make up the backbone of dna-phosphate group, and deoxyribose sugar,
What is the difference between a purine and a pyrimidine?
Purine-too wide (2 carbon rings)
Pyramidene- too narrow (1 carbon ring)
What is the name of the site where DNA replication begins?
Origins of replication
Distinguish between origin(s) of replication in eukaryotes and prokaryotes.
In eukaryotes there are many but prokaryotes is only one
replication bubble for both
Which cell type replicates DNA faster, prokaryotes or eukaryotes?
Prokaryotes
What is the name of the Y-shaped region at the end of a replication bubble where new DNA strands are elongating?
Replication fork- parental strands of DNA are being unwound
Describe what “antiparallel” means in terms of DNA structure.
- (their subunits run in opposite directions)
What direction does the DNA polymerase “read” the template strand?
3’-5’
What direction is the daughter strand synthesized? Why?
5’-3’
Differentiate between the leading strand and the lagging strand in DNA replication. What is an Okazaki fragment?
- Leading- continuous elongation
- Lagging-elongation happens in segments (Okazaki fragments= segments where elongation occurs)
What is needed for DNA polymerase to bind to in order to begin replication? Why is it necessary?
An RNA primer
What enzyme untwists the double helix and separates the template DNA strands at the replication fork?
Helicase
What does the single-strand binding protein (SSBP) do during replication?
Keep strands separated
What is the function of topoisomerase?
-relieves the strain caused by tight twisting ahead of the replication fork by breaking, swiveling, and rejoining DNA strand
What enzyme synthesizes the RNA primers?
primase
What enzyme is responsible for continually synthesizing new DNA during elongation in both the lagging and leading strands?
-DNA polymerase 3
What enzyme is responsible for removing the RNA primers and replacing them with DNA?
-DNA polymerase I
If the DNA template strand reads TACGGCAGTCTGA, what would the DNA polymerase put on the daughter strand?
ATGCCGTCAGACT
Which enzyme joins the DNA fragments together?
Ligase
What is responsible for “proofreading” the DNA strands?
DNA polymerase
What is mismatch repair? What is nucleotide excision repair?
Mismatch repair= other enzymes correct errors in base pairing
-nucleotide excision repair= a nuclease cuts out and replaces damaged stretches of DNA
What is a thymine dimer? What environmental factor has been known to cause thymine dimers on DNA?
When two thymes pair together and there’s a kick
cause-UV rays
What are telomeres? Why are they important?
chromosomal DNA molecules have special nucleotide sequences at their ends
What is telomerase? What is its function?
catalyzes the lengthening of telomeres in germ cells- under study as a target for
cancer therapies
-Lengthens telomeres to maintain long chromosomes when creating an offspring
Differentiate between prokaryotic and eukaryotic DNA structure.
Prokaryotic DNA is organized into a single circular chromosome and eukaryotic DNA is organized into several linear chromosomes.
Differentiate between location of prokaryotic and eukaryotic DNA.
Prokaryotic DNA can be found in the nucleoid region whereas eukaryotic DNA is found in the nucleus, enclosed by the nuclear membrane.
Describe chromatin, and how it involves histones. What is a nucleosome?
Chromatin= a complex of DNA and protein bound to histones,
-histones=sections of protein -Proteins called histones are responsible for the first level of DNA packing in chromatin
A nucleosome consists of DNA wound twice around a protein core of eight histones, two of each of the main histone types
Differentiate between euchromatin and heterochromatin
- This condensed chromatin is called heterochromatin;
- the more dispersed, less compacted chromatin is called euchromatin
What is “the direct manipulation of DNA for practical purposes”?
Genetic engineering
What is a plasmid? Recombinant DNA?
-plasmids, small circular DNA molecules that replicate separately from the
bacterial chromosome
-The resulting plasmid is called recombinant DNA (plasmid with foreign dna)
Explain the process of gene cloning using bacterial plasmids as vectors.
Gene of interest is inserted into a plasmid and as it replicates it creates more and more plasmid with the gen of interest
What are restriction enzymes and why are they useful?
cut DNA molecules at specific DNA sequences- to obtain only the piece needed instead of the whole thing
- Scientist use them so they can cut DNA at specific locations
What is gel electrophoresis and how is it useful?
To see the fragments produced by cutting DNA molecules with restriction enzymes, researchers use gel electrophoresis
How can PCR yield many copies of a single target DNA sequence?
produces an exponentially growing population of identical DNA molecules- heating separates them and cooling joins them.
Why is Taq polymerase used in PCR?
heat-stable DNA polymerase called Taq polymerase.
What process cuts double-stranded DNA molecules as directed by a guide RNA that is complementary to the target gene?
Cas9- a nuclease that cuts double-stranded DNA molecules as directed by a guide RNA that is complementary to the target gene
Where was the cas-9 system discovered? What is it used for?
- discovered-in bacteria
- to cut viral DNA (viruses)
What did Archibald Garrod suggest was the reasoning behind people with genetic disorders such as Alkoptonuria?
He thought symptoms of an inherited disease reflect an inability to synthesize a certain enzyme
Explain the idea behind the one gene-one enzyme hypothesis. What did researchers later revise this hypothesis to?
- each gene is responsible for producing one enzyme that affects a single step in the metabolic pathway
- revised the one gene–one enzyme hypothesis to one gene–one polypeptide
What is transcription? Translation? Where does transcription occur? Where does translation occur?
- Transcription-the synthesis of RNA using information in DNA-produces messenger RNA (mRNA)-nucleus
- Translation-the synthesis of a polypeptide, using information in the mRNA- ribosomes (RNA to protein)
What is a codon? What is their function? Where are they found?
- Three nucleotides paired together.
- they form an amino acid
- found in mRNA
Why do codons have three bases and not two or one? How many total codons are there?
3^4 because 2^4 is only 16 and there are 20 amino bases
- because they need to be transcribed into amino acids
- 64 codons
Explain the statement ‘the genetic code is redundant but not ambiguous.’
more than one codon may specify a particular amino acid but one codon can not specify more than one amino acid
What enzyme is responsible for RNA synthesis during transcription?
RNA polymerase
RNA synthesis follows the same base-pairing rules as DNA, with what exception?
Thymine becomes Uracil. Therefore the A base pairs with U instead of T.
What is the name of the region where RNA polymerase attaches during transcription?
Promoter
In Eukaryotes, what is added to the promoter region to turn the gene “on”?
Transcription factors
Name the three stages of transcription.
- Initiation
- Elongation
- termination
The complete assembly of transcription factors and RNA polymerase II bound to a promoter is called ?
transcription initiation complex
What box is crucial in forming the initiation complex in eukaryotes?
TATA box
What is the primary transcript?
the initial RNA transcript from any gene prior to processing
How are the “ends” of the mRNA modified after transcription? Do prokaryotes undergo RNA processing as well?
They get a tail and a cap.
Prokaryotes do not undergo RNA processing
What are introns? Exons?
-The noncoding regions are called intervening sequences, or introns
The other regions are called exons and are usually translated into amino acid sequences
What RNA splicing structure consists of a variety of proteins and several snRNPs?
Spliceosomes
What is a ribozyme?
RNA molecules that function as enzymes
What is alternative RNA splicing?
Many genes can give rise to two or more different polypeptides, depending on which segments are used as exons
Because of RNA splicing, the number of different proteins an organism can produce is much greater than its number of ______.
Genes
What two important structures are found at the ends of a tRNA molecule?
- anticodon on one end \
- specific amino acid on the other end
Why are molecules of tRNA not identical to each other?
Different anticodons recall for a different amino acid
What term is used to describe flexible base pairing on a codon’s third base?
Wobble
What is an anticodon? Why is it important?
base-pairs with an mRNA codon
What is the function of the enzyme aminoacyl –tRNA synthetase?
To create accurate translation. It finds a correct match between a tRNA and an amino
acid,
What two things is a ribosome composed of?
ribosomal proteins and ribosomal RNA(rRNA) (large and small subunit)
Name and describe the three binding sites on a ribosome.
- The P site holds the tRNA that carries the growing polypeptide chain
- The A site holds the tRNA that carries the next amino acid to be added to the chain (arrival)
- The E site is the exit site, where discharged tRNAs leave the ribosome (exit)
What are the three stages of translation?
- Initiation
- Elongation
- termination
What three things must be present for initiation of translation?
-mRNA template, ribosomes, tRNAs, and start codon.
During translation elongation, explain codon recognition, peptide bond formation, and translocation.
Cognon recognition= anticodon is going to recognize the codon
Peptide bond formation-amino acid from the tRNA is going to make a …
Translocation-codon moves to the next location (site)
When will translation termination occur?
when a stop codon in the mRNA reaches the A site of the ribosome
What does the release factor do to cause the release of the polypeptide?
-The release factor causes the addition of a water molecule instead of an amino acid. This reaction releases the polypeptide, and the translation assembly then comes apart
(hydrolysis)
What is a polyribosome?
Strings of ribosomes
What are the two kinds of ribosomes? What kind of proteins do they produce?
- Free ribosomes-synthesize proteins that function in the cytosol
- and bound ribosomes-make proteins of the endomembrane system and proteins that are secreted from the cell
Where does protein synthesis (translation) always begin in the cell? What determines where translation finishes?
Begins in the cytoplasm
Translation finishes when there is a stop codon
What is a mutation? A point mutation?
- Mutations are changes in the genetic material of a cell or virus
- Point mutations are chemical changes in just one nucleotide pair of a gene
What has a greater affect on a protein, base-pair substitution mutations or frameshift mutations?
Frameshift mutations
What two types of point mutations result in a frameshift mutation?
Deletion and insertion
Differentiate between a silent mutation, missense and nonsense mutations.
- Silent mutations have no effect on the amino acid produced by a codon because of redundancy in the genetic code
- Missense mutations still code for an amino acid, but not the correct amino acid
- Nonsense mutations change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein
Physical or chemical agents that can cause mutations are known as
Mutagens
(radiation(sun)/ smoking
