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