EXAM 4 Flashcards
The composition of DNA was well established by the 1950s. Models showed different arrangements of the components and sometimes introduced additional ones (such as magnesium), but all contained ______, ______, and ______.
sugars, phosphates, & bases
Chargaff’s observation suggested that _ would always pair with _ and _ would always pair with _ in a DNA molecule.
A-T and G-C
Adjacent nucleotides in the sugar-phosphate backbone are held together by the strongest type of chemical bond, __(2)__.
covalent bonds
The bonds or interactions that hold together complementary bases from opposite strands of DNA are __(2)__. These allow complementary DNA strands to _____ during S phase replication.
H-bonds - “unzip”
The bonds or interactions between stacked nucleotide units that help hold the DNA molecule together are ________.
van der Waals
The ___ end of a DNA strand has an exposed -OH group, and the ___ end has a phosphate group.
3’ - 5’
The T2 phage consists of a protein coat and DNA. It is the ____ that contains P.
DNA
After allowing phages grown with bacteria in a medium that contained 32P and 35S, Hershey and Chase used a centrifuge to separate the phage ghosts from the infected cell. They then examined the infected cells and found that they contained _____, which demonstrated that _____ is the phage’s genetic material.
labeled DNA - DNA
To elongate the lagging strand in the mandatory direction, DNA pol III must work along the other template strand in the direction __(2)__ the replication fork.
away from
The enzyme that can replicate DNA is called __(2)__.
DNA polymerase
_______ are enzymes that untwist the double helix at the replication forks, separating the 2 parental strands and making them available as template strands.
Helicases
The leading strand is built ______, but the lagging strand is built in _______.
continuously - pieces
The untwisting of the double helix causes tighter twisting and strain ahead of the replication fork, but _______ helps relieve this by breaking and rejoining DNA strands.
topoisomerase
The initial nucleotide chain that is produced during DNA synthesis is actually a short stretch of ____, not DNA. This ____ chain is called a primer and is synthesized by the enzyme _____.
RNA x 2 - primase
DNA polymerase can only add nucleotides to the ____ end of a new DNA strand.
A new DNA strand can only ELONGATE in the ____ to ____ direction.
3’ / (5’ to 3’)
Multiple primers are needed for the _____ strand, but only 1 (polymerase III) is needed for the _____ strand.
lagging - leading
______ lays down RNA primer. ______ starts at end of RNA primer and adds DNA nucleotides.
Primase - DNA Polymerase III
DNA polymerase 1 is involved in the _____ of _____ from the fragments and replacing the gap by relevant nucleotides, whereas DNA polymerase 3 is mainly involved in the ______ of the leading and lagging strands.
removal of primers
synthesis
DNA _____ closes the gap between fragments A & B on the _____ strand.
ligase - lagging
The correct DNA replication model is _____ and produces 2 double helices: ____ dark blue and ____ light blue strand per double helix in the 1st replication.
The 2nd replication produces 4 double helices: 2 of them each have 1 dark & 1 light blue strand, while the other 2 both have ____ blue strands.
semiconservative - 1 & 1 - light blue (or daughter DNA)
The evolutionary significance of altered DNA nucleotides is that _____ are the source of genetic _____ upon which natural selection operates. Sequence changes may become ____ and be _____ down to next generation.
mutations - variation
permanent - passed
If chromosomes of germ cells became shorter each round of cell division, this could cause essential genes to be _____ from the ____ they produce. The enzyme _____ catalyzes the lengthening of telomeres in germ cells.
missing - gametes - telomerase
Not all cells have active telomerase (catalyze lengthening of telomeres in germ cells), but high ____ cells do.
In cancer cells, telomerase can be turned __(2)__ and allow division when they shouldn’t!
turnover
back on
Proteins called ____ are responsible for the first level of DNA packing in chromatin and there are ____ types.
histones - 4
_____ are like beads on a string and consists of DNA wound 2x around a protein core of 8 _____.
Nucleosomes - histones
Because of its compaction, ______ DNA is largely ______ to the machinery in the cell responsible for transcribing the genetic information coded in the DNA.
heterochromatic - inaccessible
Understanding DNA structure and replication makes genetic _____ possible. The 2 strands of DNA are _____ to each other, which is the basis for nucleic acid ______.
engineering - complementary - hybridization
Common tools for genetic engineering include recombinant ____, DNA c____, r_____ enzymes, gel e____, and PCR.
DNA - cloning - restriction - electrophoresis
Gene cloning/engineering rely on use of ______ enzymes that cut DNA molecules at specific locations.
restriction
DNA is ______ to messenger RNA (mRNA), and the mRNA is _____ to proteins on the ribosomes.
transcribed - translated
Transcription begins when a molecule of RNA polymerase binds to a _____. Then RNA poly ____ gene. Once it reaches the ______, it exits the gene and releases RNA.
promoter - transcribes - terminator
RNA molecules do not have () or ____ like DNA does. Instead it has () or ____. Base pairing between DNA & DNA is always A-_ and G-_, but when DNA pairs w/ RNA it is A-_ and G-_.
T or thymine - U or uracil
A-T and G-C / A-U and G-C
Synthesis of _____ is not directly coded in DNA, but it is for mRNA, p_____, & DNA.
organelles - proteins
A gene has 2 main parts, a regulatory region containing a _____ and a transcription region which contains the _____ information for a protein product.
promoter - coding
A sequence of 3 nucleotides on an mRNA molecule is called a ______. What codon codes for _____ and functions as a start signal?
codon - Methionine (met) - AUG
When RNA is modified before translation, it is called RNA ______. During this time, a __(2)__ nucleotide is added to the ____ end as a “cap”.
processing - modified guanine - 5’
During RNA processing, a _____ tail is added to the ____ end of the RNA.
poly-A - 3’
______ delete portions of the RNA called _____ and connect remaining segments called ______ or expressed regions.
Spliceosomes - introns
exons
Translation or protein _______ takes place in the ______ at the _____.
synthesis - cytosol - ribosome
________ is the process by which the ribosome slides down the mRNA so a new cycle of elongation can begin.
Translocation
Triplets of RNA bases are called _____. A ribosome facilitates the pairing of each mRNA ______ w/ a particular tRNA a_______.
codons - codon - anticodon
What can RNA polymerases (i.e., primase) do that DNA polymerases cannot?
RNA polymerases (primase) can add new nucleotides w/o the 3’ -OH group, but DNA polymerases cannot.
Gene cloning is useful for two basic purposes: to make many ______ of (or amplify) a particular gene and to produce a _____ product from it.
copies - protein
Gene Cloning using copies of GENE:
1. Gene for _____ resistance is inserted into plant.
2. Gene is used to alter ______ for cleaning up _____ waste.
pest
bacteria - toxic
Gene Cloning using harvested PROTEIN product:
1. HGH used to treat ______ growth.
2. Protein dissolves blood _____ in heart attack therapy.
stunted
clots
Gene cloning and genetic engineering generally rely on the use of enzymes that cut DNA molecules at a _______ number of specific locations. These enzymes are called __(2)__.
limited - restriction enzymes
Proteins are the link between genotype and phenotype.
Gene expression is the process by which DNA directs the synthesis of _______ (or, in some cases, just _____).
The ______ of genes that code for proteins includes two stages: transcription and translation.
proteins - RNAs
expression
Proofreading corrects many errors, but sometimes a few get through. Mismatch ______ helps catch and remove these errors right after DNA synthesis. __(2)__ then replaces the missing errors.
repair - DNA polymerase
Some genes don’t encode ______. Some genes actually encode functional ______ molecules instead.
polypeptides - RNA
The genetic code is r______, not _______, and nearly ______.
redundant - ambiguous - universal
The start codon for RNA is always __ U __ that codes for the AA ______.
AUG - Met
The 3 stop codons are UAA, UAG, and _____.
UGA
The codons are read by the translation machinery in the ___ to ___ direction along the mRNA.
5’ –> 3’
The 3 stages of transcription include: initiation, ______, and t______.
elongation - termination
Several transcription _____ bind to the DNA.
RNA poly II attaches to and initiates transcription at the ______.
Transcription initiation _____ forms.
The stretch of DNA downstream from the promoter that is transcribed into an RNA molecule is called a __(2)__.
factors - promoter - complex - transcription unit
There are 3 RNA polymerases:
RNA poly I makes _____ transcripts.
RNA poly II makes _____ which code for proteins.
RNA poly III makes _____ and plays a role the translation process.
rRNA
mRNA
tRNA
During termination of transcription:
Bacteria trxn proceeds through a ______ sequence in the DNA and the transcript goes straight to translation.
In eukaryotes, RNA polymerase II transcribes a sequence on the DNA called the _______ signal sequence, which specifies a “signal” (AAUAAA) in the pre-mRNA. The pre-mRNA requires further _____ before translation.
terminator
polyadenylation - processing
The modified ends may promote the export of _____ from the nucleus, and they help protect it from ______.
mRNA - degradation
A modified __(2)__ is added to the ___ end of the pre-mRNA, which is synthesized first, after the first 20–40 nucleotides have been transcribed.
guanine nucleotide - 5’
At the ___ end, an enzyme then adds 50–250 more adenine (A) nucleotides, forming a __(2)__.
3’ - poly-A tail
The stretch of DNA downstream from the promoter that is transcribed into an RNA molecule is called a __(2)__.
transcription unit
What mediates the binding of RNA polymerase and the initiation of transcription? (a collection of proteins)
transcription factors
The 5′ UTR and 3′ UTR do not code for _______, but they are parts of ________ because they remain in the mRNA.
protein - exons
_______ RNA ______ is a type of eukaryotic gene______ at the RNA-processing level in which different mRNA molecules are produced from the same primary ______, depending on which RNA segments are treated as exons and which as introns.
alternative RNA splicing - regulation - transcript
BC of alternative RNA splicing, the number of different protein products an organism produces can be much greater than its number of _______.
genes
_____ translates the “message” from mRNA and transfers __(2)__ from the cytoplasm to the growing polypeptide in a _____ via ___ bonds.
tRNA - amino acids - ribosome - H-bonds
