Test 4
Albinism occurs when both alleles at a locus produce defective enzymes in the biochemical pathway leading to melanin. Given heterozygotes are normally pigmented which statement is correct?
1 allele produces as much melanin as 2 normal alleles
Pleiotrophy
1 gene has multiple effects on phenotype
Template Strand
1 of 2 DNA strands that provides a template for mRNA transcript
Histone Modifications
1. Acetyl groups (less positive)= LOOSENS chromatin structure; creates straight-line structure of histones 2. Methyl Groups (MORE positive)= CONDENSE chromatin; balls up histones 3. Phosphate groups next to a methylated amino acid= LOOSEN chromatin
The steps of processing that occur to nearly all human mRNA includes?
1. All functioning mRNA must undergo capping and polyadenylation 2. Vast majority of mRNAs in high eukaryotes undergo splicing
Eukaryotic Vs. Prokaryotic Transcription
1. In prokaryotes, mRNA produced by transcription is immediately translated. Known as coupled transcription and translation. 2. In eukaryotes, the nuclear envelope separates transcription from translation; separated in time and space
What are the final products of an expressed gene?
1. Polypeptide chain 2.tRNA molecule 3.rRNA molecule
Termination of Transcription
1. Prokaryotes: Polymerase stops transcription at the end of Terminator Sequence 2. Eukaryotes: Polymerase transcribes the polyadenylation sequence (AAUAA) which signals transcription complex to Stop. 3. Completed mRNA disassociates when its finished and DNA helix twists up again
Translation
1. Ribosomes are protein making machines 2. tRNA; transfer RNA delivers specific amino acid to Ribosome
Purpose of 5' Cap and Poly-A tail
1. They seem to facilitate export of mRNA 2. Protect mRNA from hydrolytic enzyme 3. Help ribosomes attach to 5' end
DNA fingerprinting steps
1. extract DNA 2.Amplify DNA by PCR 3. Cut the DNA with restriction enzyme 4. Separate the DNA pieces by gel electrophoresis
What are the 3 types of RNA used in translation/ protein synthesis?
1. mRNA: Messenger RNA; Transcribes the genetic code from DNA into a form that can be read and used to make proteins. Carries information from Nucleus to the Cytoplasm 2. rRNA: Ribosomal RNA; located in Cytoplasm of cell, where ribosomes are found. Directs translation of mRNA into proteins 3. tRNA: Transfer RNA; located in Cytoplasm, transfers amino acids to the ribosome that correspond to the 3- nucleotide codon of rRNA. Amino acids then can be joined together to make polypeptides and proteins.
Ribosomes
1.Composed of 2 protein subunits and ribosomal RNA; rRNA 2. Found free in cytosol and attached to rough ER
DNA VS. RNA
1.DNA is double stranded; RNA single stranded 2. DNA's sugar is DeOxyribose; RNA is Ribose sugar. 3. DNA has thymine; RNA has uracil
Initiation of Transcription
1.Promoters signal initiation of RNA synthesis; in Eukaryotes starts at TATA box 2. Transcription initiation complex
Alternative RNA splicing
1.Some genes encode more than 1 kind of polypeptide 2.Allows the production of proteins of different sizes from a single mRNA 3. # of proteins an organism can produce is Much greater than # of genes
father diagnosed with homozygous dominant disease. No one else in family, including wife, has the disease. What is the probability his daughter will receive disease allele from dad?
100%
Cytosine makes up 38% of the nucleotides in a sample of DNA from an organism. What is the percent of nucleotides in this sample would be Thymine?
12%, because C=38% then G=38%, 100%-76%= 24% of A and T, so 12% A and 12% T.
Helicase
1st enzyme: untwists double helix at replication forks; separating 2 parental strands and making them available as template strands
F1 generation
1st generation of offspring obtained from an experimental cross of 2 organisms
Law of Segregation
1st law of heredity states: Pairs of alleles for a trait separate when gametes are formed
If proteins were composed of only 12 different kinds of amino acids, what would be the smallest possible codon size in a genetic system with 4 different nucleotides?
2 nucleotides; because 1 nucleotide per amino acid=4^1= 4 options. 2 nucleotides per amino acid=4^2= 16 options; so 2 nucleotides
Double Helix
2 strands of nucleotides wound about each other; structure of DNA
Single-strand binding proteins
2nd enzyme: Proteins that bind to and stabilize single strands of DNA exposed when helicase unwinds double helix in preparation for replication
f2 generation
2nd generation of offspring, obtained from an experimental cross of 2 organisms; offspring of f1 generation
Law of Independent Assortment
2nd law of heredity states: that genes separate independently of one another in meiosis
A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is?
3' UCA 5'
In what order to the following enzymes and polypeptides function during replication? 1. single-strand binding protein 2. DNA Polymerase II 3. Helicase 4. Primase 5. Ligase 6. DNA Polymerase I
3,1,4,2,6,5
Primase
3rd enzyme: Joins RNA nucleotides to make the primer
DNA polymerase II
4th enzyme: Synthesizes DNA new base pairs
How are Eukaryotic genes regulated?
5 steps: 1. Access to gene 2. Transcription 3. RNA modification 4. translation 5. Protein Degradation
DNA polymerase I
5th enzyme: Joins individual nucleotides to produce DNA molecule
Ligase
6th and last enzyme: Eventually joins sugar-phosphate backbones of Okazaki fragments
Gel electrophoresis
A gel made of polymer that acts as a molecular sieve to separate nucleic acids or proteins on basis of size, electric charge, and other physical properties
Each of a group of bacteria cells has a mutation in its lac operon. What would make it impossible for the cell to metabolize lactose?
A mutation in the lac repressor that prevents from binding to inducer allolactose
Silent mutation
A mutation that changes a single nucleotide, but does not change the amino acid created
Frameshift Mutation
A mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide
trp operon
A repressible protein, contains genes to SYNTHESIZE Tryptophan
Corepressor
A small molecule that cooperates with a repressor protein to switch operon OFF Ex: trp repressor is active only in the presence of its COREPRESSOR trytophan
Adenine is found in all members of which group?
ATP, RNA, and DNA
DNA methylation
Addition of METHYL groups to certain bases in DNA (usually CYTOSINE)= REDUCED transcription
Polygenic Inheritance
Additive effect of 2 or more genes on a single phenotype
What happens in the presence of lactose?
Allolactose serves as an INDUCER and binds to and inactivates the repressor to turn lac operon on
A specific gene is known to code for 3 different but related proteins how is this possible?
Alternative RNA splicing
When the ribosome reaches a stop codon on the mRNA, no corresponding tRNA enters the A site. If the translation reaction were to be experimentally stopped at this point( before release factor function), which of the following would be able to isolate?
An assembled ribosome with a polypeptide attached to the tRNA in the P-site
trp operon
Anabolic, repressible. Operon codes for enzymes to make trp, so its active without trp: repressible. repressor molecule activates repressor protein so genes can function.
Mutagen
Any agent (physical or environmental) that can induce a genetic mutation or can increase the rate of mutation
Transcription Initiation Complex
Assembly of transcription factors and RNA polymerase II bound to promoter
Signal Recognition Particle
Binds to signal sequence and the ribosomal subunits and transports the complex to the ER
A new form of DNA is discovered that appears to be able to replicate itself in both 3'-5' direction and in 5'-3' direction. If this is true, how would this newly discovered DNA replication differ from DNA replication as we know it?
Both strands could be leading, rather than 1 that is leading and 1 that is a lagging strand
How is a lac operon subject to positive control?
By a stimulatory protein. -Activated by a CAP protein
How is the lac operon activated?
By the CAP protein
How are parents or killers identified?
By their specific genetic profile; genetic markers that vary in population can be analyzed for a given person to determine that individuals unique set of genetic markers
mutation
Change in DNA sequence that affects genetic information
Quantitative Characters
Characters that vary in population along a continuum
Transcription factors
Collection of several proteins that must bind to DNA before RNA polymerase II can do so
Proteasome
Complexes that DEGRADE proteins; tags proteins only needed for a short time
Huntington's Disease
Degenerative disease of the nervous system caused by lethal dominanat allele that has no effect until the individual is 35-45 years old
What can siRNAs and miRNAs do?
Degrade mRNA or BLOCK its translation
alleles
Different forms of a gene
Lagging strand
Discontinuously synthesized DNA strand that elongates direction away from replication fork
Aminoacyl-tRNA synthetase
Enzyme that correctly matches between tRNA and an amino acid
Nuclease
Enzyme that hydrolyzes DNA and RNA into their component nucleotides
What is RNA processing?
Enzymes in Eukaryotic nucleus modify pre-mRNA before genetic messages are dispatched to cytoplasm 1. Both ends of the Primary transcript are usually altered 2. Some interior parts of molecule are cut out
Exons
Expressed sequence of DNA; codes for Proteins
Does transcription factor binding to enhancer control elements always results in increased transcription of the corresponding gene?
False
If the release factor has not seperated the translational machinery what would you do?
Find a ribosome on a mRNA with an empty A and P-site with a tRNA and polypeptide chain
Wobble
Flexible pairing at the 3rd base of a codon and allows some tRNAs to bind to more than one codon
Operon
Found in BACTERIA. The entire stretch of DNA that INCLUDES operator, promoter, and the genes that they control
Who conducted x-ray diffraction studies were key to discovery of structure of DNA?
Franklin
Tay-Sachs disease
Genetic disease caused by recessive allele for dysfunctional enzyme, leads to accumulation of certain lipids in the brain. Seizures, blindness, and degeneration of motor and mental skills usually manifest a few months after birth
Cystic Fibrosis
Genetic disorder caused by recessive allele for chloride channel protein
Sickle Cell Anemia
Genetic disorder where erythrocytes take an abnormal curve or "sickle" shape
Anticodon
Group of 3 base-pairs on a tRNA molecule that are complementary to an mRNA codon
TATA box
Happens in eukaryotes when transcription factors mediate the binding of RNA polymerase to a signal within the promoter
Topoisomerase
Helps relieve strain in double helix ahead of replication fork
What are the bonds that hold the 2 antiparallel strands of DNA together?
Hydrogen Bonds
Where do repressible enzymes usually function?
In ANABOLIC pathways. Repressed by high levels of the end product
Where do inducible enzymes usually function?
In CATABOLIC pathways. Induced by a chemical signal
What are way genetic engineering is used in agriculture and medicine?
In agriculture one way is they create genetically modified foods that are resistant to bugs or creating bacteria that clean up toxic waste Medicine uses things like human growth hormone to make people grow taller and another way is they extract protein to dissolve blot clots in the heart attack therapy
3 Stages of Translation
Initiation, Elongation, and Termination
During what stage in the cell cycle does DNA replication occur?
Interphase
What happens in the absence of lactose in the lac operon?
It is TURNED off
What happens in the presence of lactose in the lac operon?
It is TURNED on
What is transcription?
It is the synthesis of messenger RNA, mRNA under the direction of DNA
Compare and contrast the lac operon and the trp operon
Lac operon: catabolic, inducible. Operon codes for enzymes to metabolize lactose, so it's inactive without lactose. Inducer inactivates repressor so genes can be transcribed. Trp Operon: Anabolic, repressible. Operon codes for enzymes to make trp, so its active without trp: repressible. repressor molecule activates repressor protein so genes can function.
Spliceosomes
Large molecular machine composed of a variety of proteins and several small nuclear ribonucleoproteins (snRNPs)
What does DNA methylation cause?
Long-term inactivation of genes. Causes chromatin tightening and reduces transcription
multifactorial
Many factors both genetic and environmental; influence phenotype
hybridization
Mating or crossing of 2 true breeding varieties
Semiconservative
Method of replication that implies each new strand of DNA is half original and half new
5' Cap
Methylated guanine nucleotide added to the 5' end of eukaryotic mRNA
miRNA
MicroRNA; small single stranded RNA molecules that bind to mRNA
Poly-A tail
Modified end of 3' end of mRNA molecule consisting of the addition of 50-250 adenine nucleotides
Missense mutation
Most common type of mutation; a base- pair substitution in which the new codon makes sense in that it still codes for an amino acid
Addition mutation
Mutation involving the addition of 1 or more nucleotide pairs to a gene
Point mutation
Mutation that affects a single nucleotide usually by substituting 1 nucleotide for another
Nonsense mutation
Mutation that changes an amino acid codon to 1 of 3 stop codons resulting in a shorter and usually nonfunctional protein
inducable operon
Negative Gene regulation. Usually OFF, inactivates the repressor and TURNS ON transcription
repressible operon
Negative Gene regulation.Usually ON, binding of repressor to the operator shuts off transcription
What is the regulation of the trp and lac operons involve?
Negative control of genes because operons are switched OFF by the ACTIVE form of the REPRESSOR
Components of RNA
Nitrogenous base, 5-carbon sugar, and a phosphate group. Adenine-Uracil and Guanine-Cytosine
Does translation of tRNA and rRNA occur?
No
Introns
Noncoding regions; intervening sequences
Pleiotropy
One gene is able to affect multiple phenotypic characters Ex: Sickle-cell Disease
Antiparallel
Opposite arrangement of sugar-phosphate backbones in a DNA double helix
Polymerase Chain Reaction
PCR; Any specific target gene segment within 1 or more DNA molecules can be quickly amplified in a test tube
P generation
Parental generation; 1st two individuals that mate in a genetic cross
Components of DNA
Phosphate, Deoxyribose sugar, and a Nitrogen base. Adenine-Thymine and Cytosine- Guanine
How are adjacent sugars held together?
Phosphodiester Bonds
Addition Rule
Probability that 1 of 2 mutually exclusive events will occur is calculated by adding together their individual probabilities
Gene Expression
Process by which DNA directs protein synthesis, includes 2 stages: transcription and translation
Nucleotide excision repair
Process of removing and then correctly replacing damaged segments of DNA using undamaged strand as guide
Degradation occurs in regulatory components?
Proteasomes and siRNA
Activator protein
Protein that binds to DNA and stimulates transcription of a specific gene
Repressor protein
Protein that binds to the operator in an operon to switch off transcription
RNAi
RNA interference; inhibition of gene expression by RNA molecules
Elongation of RNA strand
RNA polymerase moves along DNA and untwists Double Helix
How does transcription work?
RNA synthesis is catalyzed by RNA polymerase> Initiated at promoter sequence> Stopped at terminator sequence in Prokaryotes and Eukaryotes are downstream of polyadenylation sequence
Norm of reaction
Range of phenotypic possibilities due to environmental influences
Reading frame
Read in correct order for specified polypeptide to be produced
What do snRNPs do?
Recognize certain sequences (splice sites) at the end of introns which tell splicesome to remove the sequence from pre-mRNA
Operator
Region of DNA that controls RNA polymerase access to a set of genes with related functions
What hapens when operons are switched off by the active form of the repressor?
Regulation of trp and lac operons involve NEGATIVE control of genes
RNA splicing
Removes introns and joins exons creating mRNA molecule with continuous coding sequence
telomeres
Repeated DNA sequences at the ends of eukaryotic chromosomes
Multiplication Rule
Rule that determines probability, we multiply probability of one event by another
chorionic villus sampling
Sampling of placental tissue for microscopic and chemical examination to detect fetal abnormalities
Control Elements
Segments of noncoding DNA that help regulate transcription by BINDING certain transcription factors
Polyribosomes
Several ribosomes attached to 1 messenger RNA molecule
Okazaki fragments
Short fragments of DNA that are the result of synthesis of the lagging strand during DNA replication
siRNAs
Small interfering RNAs; which causes RNAi
Primer
Starting point for DNA synthesis; Already existing RNA chain bound to template DNA to which DNA nucleotides are added during DNA synthesis
Signal peptide
Stretch of amino acids on a polypeptide that targets the protein to a specific destination in a eukaryotic cell
Nontemplate strand of DNA: 5' ATG TAT GCC AAT GCA 3' What is the template strand, mRNA, Anticodons on complementary tRNA.
Template Strand: 3' TAC ATA CGG TTA CGT 5' mRNA: 5' AUG UAU GCC AAU GCA 3' Anitcodons on complementary tRNA: 3' UAC AUA CGG UUA CGU 5'
What does the operon model attempt to explain?
The coordination control of gene expression in bacteria
What happens in the absence of lactose?
The lacl repressor is active and switches lac operon off
Deletion mutation
The loss of 1 or more nucleotides from a gene by mutation; the loss of a fragment of a chromosome
What does the operator, the promoter, and the genes that they control make-up?
The operon
The first event to take place in translation in Eukaryotes is?
The small subunit of the ribosome recognizes and attaches to the 5' end of mRNA
What is translation?
The synthesis of a polypeptide under the direction of mRNA by ribosomes
What happens when all required transcription factors bound to their appropriate control elements and the gene must be free of any form of repressor?
To have increased transcription of the corresponding gene
What is the definition of a gene as a transcribed segment of DNA?
Transcription is the syntheis of a mRNA; messenger RNA under the direction of DNA
tRNA
Transfer RNA; consists of a single RNA strand. Looks like cloverleaf when folded structure. Not identical. Amino acid at one end and has anticodon on the other end
Nucleotide- pair substitution
Type of point mutation in which one nucleotide in a DNA strand and its partner in the complementary strand are replaced by another pair of nucleotides
A group of genes that function in the same metabolic pathway are grouped together where?
Under 1 promoter
epistasis
a gene at one locus alters the phenotypic expression of a gene at a second locus
If a segment of DNA (circular or looped) is able to replicate, it must include what?
at least 1 origin of replication
nucleosomes
bead-like structures formed by histones and DNA
inducer
binds to and inactivates the repressor to turn the lac operon on
Lac operon
catabolic, inducible. Operon codes for enzymes to metabolize lactose, so it's inactive without lactose. Inducer inactivates repressor so genes can be transcribed.
punnet square
chart that shows all possible combinations of alleles that result from a genetic cross
Codominance
condition in which both alleles for a gene are fully expressed
Leading Strand
continuous complementary DNA strand synthesized along the template strand; 5'-3' direction
Incomplete dominance
creates a blended phenotype; one allele is not completely dominant over the other
Dihybrid cross
cross between 2 individuals that have different alleles for the same gene
Monohybrid cross
cross between 2 individuals that involves 1 pair of contrasting traits
test cross
crossing of 2 individuals of unknown genotype with a homozygous recessive individual to determine unknown genotype
cAMP
cyclic AMP; happens when glucose is scarce; it accumulates and binds to CAP activating the CAP.
nucleoid
dense region of DNA in prokaryotic cell
Pedigree
diagram that shows the occurrence of a genetic trait in several generations of a family
e-site
exit site, where discharged tRNAs leave the ribosome
trait
genetically determined variant of a characteristic
Homozygous
having identical alleles for trait
Heterozygous
having two different alleles for a trait
character
heritable feature varies among individuals
p-site
holds most current tRNA that is attached to growing polypeptide
a-site
holds tRNA that carries next amino acid to be added to the chain
repressor
inhibits expression of a gene
Difference between Leading and Lagging strand
leading strand synthesized in the same direction as movement of replication fork; lagging strand is synthesized away from replication fork
chromatin
long strands of DNA found in Eukaryotic cell nucleus, condense to form chromosomes
Codons
mRNA base triplets, read in 5'-3' direction
A transcription unit that is 8,000 nucleotide long may use 1,200 nucleotides to make a protein consisting of approximately 400 amino acids. This is best explained by the fact that?
many noncoding stretches of nucleotides are present in mRNA
heterochromatin
nontranscribed eukaryotic chromatin; highly compacted visible with light microscope during interphase -Chromatin condensed
What are the 3 binding sites on a ribosomes?
p-site, a-site, and e-site
genotype
particular alleles at specified loci present in an organism
phenotype
physical characteristic of an organism
DNA replication
process of making a copy of DNA
histones
protein molecule around where DNA is tightly coiled in chromatin
euchromatin
region of DNA that is uncoiled and undergoing active transcription into RNA -Loosely packed chromatin
Complete dominance
relationship in which one allele is completely dominant over another
Origin of replication
site where replication of DNA molecule begins, consisting of specific sequence of nucleotides
Activator
stimulates transcription of a gene
Amniocentesis
technique for determining genetic abnormalities in a fetus by presence of certain channels or defective fetal cells in amniotic fluid
What enzyme do some cells include that compensates for replication-associated shortening
telomerase
Transformation
transfer of genetic material in the form of DNA fragments from 1 cell to another from 1 organism to another
true breeding
used to describe organisms that produce offspring identical to themselves if allowed to self-pollinate
Replication fork
y-shaped region on replicating DNA molecule where new strands are growing
