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Module 2 - Genetics (2)
Part 2 (after midterm)
Terms in this set (176)
RNA-directed synthesis of a polypeptide
- genetic information flows from mRNA to protein
A cell translates an mRNA message into protein with the help of ______
transfer RNA (tRNA)
What is the function of tRNA?
transfer amino acids from the cytoplasmic pool of amino acids to a growing polypeptide in a ribosome
Ribosomes facilitate specific coupling of...
tRNA anticodons with mRNA codons in protein synthesis
the 2 ribosomal subunits (large and small) are made of _____ and ______ ______
ribosomal RNA (rRNA)
- subunits are not functional on their own, need both of them
bacterial and eukaryotic ribosomes are somewhat similar but have significant differences in their ______ _____
there are specific _____ and ______ in each ribosome subunit.
Both info are coded for in DNA, which are translated?
rRNA and proteins
rRNA : rRNA genes are transcribed but NOT translated
protein : protein genes are transcribed AND translated
____ is the most abundant type of cellular RNA because most cells contain thousands of _____
A ribosome has __ binding sites for tRNA. What are they and what is their function?
P site = holds the tRNA that carries the growing polypeptide chain - where the peptide bond is formed between amino acids
A site = holds the tRNA that carries the next amino acid to be added to the chain - tRNA brings in an amino acid based on codon present on mRNA, then next 3 bases (codon) is read for another amino acid
E site = exit site, where discharged tRNAs leave the ribosome - tRNA that was bound to the amino acid exits after the peptide is formed
As the polypeptide becomes longer, it passes through an _____ ____ in the ribosome's _____ subunit.
When the polypeptide is complete, it is released through the _____ _____.
Translation requires the participation of multiple types of RNA. What are the types and what is their function?
messenger RNA (mRNA) = carries the information from DNA that encodes proteins
ribosomal RNA (rRNA) = structural component of the ribosome
transfer RNA (tRNA) = carries amino acids to the ribosome for translation
When a codon is read, the ____ asks for a certain ___ ___ to be brought in.
_____ brings an ____ by undergoing a chemical reaction to attach the amino acids to the tRNA, then it comes in to ribosome and attaches to ____ at the __ ____.
When next tRNA comes in for next codon, the previous tRNA moves to ___ ____ and forms ____ ____ to joins its amino acid to the other amino acids of the _______ _____.
tRNA then moves to ___ ____ and ______ ______.
a charged tRNA binds to the __ ____ if its anticodon is _______ to the codon at the ___ _____
An enzyme in the ribosome responsible for peptide bond formation during translation.
ribosome moves down (reads) the _____ in a ____ to ____ direction.
elongation continues until the ribosome encounters a ____ _____
5' to 3'
molecules of tRNA are not ______.
each carries a ____ _____ _____ on one end.
the other end is an ______ that ________ with a _______ ________ on mRNA
specific amino acid
5' and 3' ends of the linear tRNA are both located ____ _____ ____.
The protruding ___ end acts as ____ ______ for ______ _____.
Loop extending from the other end includes the ______.
near one end
attachment site for amino acid (amino acid arm)
anticodon is written __ to __ to align properly with codons written __ to __
3' to 5'
5' to 3'
tRNA molecule is a ______ in the sense that it (in the context of the ribosome), it can read a ____ ____ word and interpret it as a _____ word
nucleic acid word (mRNA codon)
protein word (amino acid)
Accurate translation of a genetic message requires 2 steps of molecular recognition
1. correct match between a tRNA and an amino acid, done by the enzyme Aminoacyl-tRNA Synthetase
2. pairing of the tRNA anticodon with the appropriate mRNA codon
- active site of each type fits only a ______ _____ of ______ ____ and ______
An enzyme that joins each amino acid to the appropriate tRNA
Aminoacyl-tRNA synthetase catalyzes the _______ attachment of the amino acid to its tRNA in a process driven by the ________ of ______.
The resulting ________ ____ is released from the enzyme and is then available to deliver its ______ ____ to a growing _____ _____ on a ______.
hydrolysis of ATP
aminoacyl tRNA (charged tRNA)
some tRNAs must be able to bind to ____ _____ _____ ______.
more than one codon
the rules for base pairing between the third base of a codon and the corresponding base of a tRNA are ______/_______ compared to other positions
relaxed / not specific
flexible base pairing at 3rd codon position
- 3rd codon base can pair with more than one nucleotide of anticodon
__ end of codon and ___ end of anticodon has the wobble
start codon (codes for Met)
- has to be first codon
- Met is kept only if it is meant to be
- if Met is not meant to be kept, peptide bond is broken and Met is released
UAA, UAG, UGA
- stops the growing of polypeptide
- mRNA is released
what makes polypeptides different, with different functions/roles?
sequence of amino acids
What are the 3 stages of translation? What happens at each stage?
1. Initiation = brings together mRNA, tRNA bearing the first amino acid of the polypeptide, and 2 subunits of a ribosome
2. Elongation = amino acids are added one by one to the preceding amino acid, peptide bonds are formed
3. Termination = when the ribosome reaches a stop codon in the mRNA, the polypeptide is release and the mRNA is released, and the 2 ribosomal subunits dissociate
_____ ______ is a stretch of amino acids on a polypeptide that targets the protein to a specific destination in a eukaryotic cell.
______ ______ ______ is a protein-RNA complex that recognizes a signal peptide as it emerges from a ribosome and helps direct the ribosome to the endoplasmic reticulum (ER) by binding to a receptor protein on the ER.
signal recognition particle (SRP)
A group of several ribosomes attached to, and translating, the same messenger RNA molecule.
coding sequence is the region of a ____ that makes the _____
- determines the _____ of ______ ____ in the ______
- gene , RNA
- sequence of amino acids in the protein
Terminator is a special _____ of _______ in ____ that marks the ____ of a ____.
- signals ____ _______ to release the newly made ____ molecule, which then departs from the ____
sequence of nucleotides in DNA
marks the end of a gene
- RNA polymerase
__________ is a specific region of a gene where RNA polymerase can bind and begin transcription
______ ______ are sections of DNA that are involved in controlling the activity of genes
- promotor and controlling site (where induction occurs)
lacI+ gene codes for a _______ ________
When lactose does NOT need to be broken down, the _______ ________ _______.
repressor BLOCKS operator
- genes that code for enzyme that breaks down lactose are NOT being translated
- repressor protein acts as a "road-block" that RNA Polymerase can't pass
When lactose needs to be broken down, _______ joins with ____ ____ which changes the shape of the protein so that it is no longer able to ______ _____.
______ _____ can then move along and transcribe the other __ genes.
3 : lacZ+ and lacY+ and lacA+
Coding sequence is not enough for a gene to be transcribed and translated. You need the right ____ _____ too.
- control comes from regulatory sequences as to whether or not the gene will be allowed to express
changes in the genetic material of a cell or virus
- mutations of 1 or a few nucleotides can affect protein structure and function
______ are the ultimate source of new genes
chemical changes in just one base pair of a gene
point mutations within a gene can be divided into 2 general categories
1. Single Nucleotide-Pair Substitutions
2. (one or more) Nucleotide-Pair Insertions or Deletions
purine to purine or
pyrimidine to pyrimidine
purine to pyrimidine
or vice versa
gene is a region of DNA that can be ______ to produce a final functional product that is either a ______ or and _____ _______
incorrect nucleotide is added to a growing chain during replication
- incorrect base will be used as a template in the next round of replication
A chemical or physical agent that interacts with DNA and causes a mutation.
the replacement of one nucleotide and its partner with another pair of nucleotides
have no effect on the amino acid produced by a codon because of redundancy in the genetic code
- no observable effect on the phenotype
- codon changes but new codon still codes for same amino acid
still code for an amino acid, but not the correct amino acid
- change one amino acid to another one
- different amino acid leads to a changed polypeptide (same length but has a diff AA)
change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein
- causes translation to be terminated prematurely
- shortens polypeptide (the less AA that get coded the more severe the consequences)
- even if it's on of the last ones, protein is still affected
A single nucleotide is replaced by a different nucleotide
insertion and deletion mutations
additions or losses of nucleotide pairs in a gene
- these mutations have a disastrous effect on the resulting protein more often than substitutions do
Insertion or deletion of nucleotides may alter the _____ ______ of the ______ ____
- the triplet grouping of nucleotides on the mRNA that is read during translation
occurs whenever the number of nucleotides inserted or deleted is not a multiple of 3
- all nucleotides downstream of the insertion/deletion will be improperly grouped into codons
- result will be extensive missense mutations
- usually ending sooner or later in a nonsense mutation that leads to premature termination
Unless the frameshift mutation is very near the end of the gene, the protein is almost certain to be _______
- many different amino acids will be affected
blending hypothesis of inheritance
idea that genetic material from the 2 parents blends together
- predicts that over many generations, a freely mating population will give rise to a uniform population of individuals, something we don't see
When the hybrids were crossed with each other, some of the offspring resembled the ______ _____ rather than the ______ ______
- this evidence contradicted the idea that traits are DIRECTLY passed from parent to offspring
Particulate Hypothesis of Inheritance
idea that parents pass on discrete heritable units (genes) that retain their separate identities in offspring
Mendel documented a ______ _________ through his experiments with garden peas
Advantages of pea plants for genetic study (5)
-There are many varieties with distinct heritable features, or characters (such as flower color); character variants (such as purple or white flowers) are called traits
-Mating of plants can be controlled and easy to grow
-Each pea plant has sperm-producing organs (stamens) and egg-producing organs (carpels)
-Cross-pollination (fertilization between different plants) can be achieved by dusting one plant with pollen from another
character is a _____ _____ that _____ among individuals
- each variant for a character is called a _______
Mendel chose only those characters or traits who had __ _______ ______.
He used varieties that were _____-_______
2 alternate forms (variations)
Plants that produce offspring of the same variety when they self-pollinate.
__________ is the the mating, or crossing, of 2 contrasting, true-breeding varieties
What are the 3 generations that Mendel observed?
P generation = true-breeding parents
F1 generation = hybrid offspring of the P generation
F2 generation = offspring when F1 individuals self-pollinate
A cross between individuals that involves one pair of contrasting traits
(ex: T and t)
Mendel called the purple flower color a _________ trait and the white flower color a _______ trait
Mendel developed a hypothesis to explain the 3:1 inheritance pattern he consistently observed in F2 offspring
4 parts of Mendel's model
1. alternative versions of genes (alleles) account for variations in inherited characters
2. for each character, an organism inherits 2 copies (2 alleles) of a gene, one from each parent
3. if the 2 alleles at a locus differ, then one, the dominant allele, determines the organism's appearance. The other, the recessive allele, has no noticeable effect on the organism's appearance
4. Law of segregation
alternative versions of a gene
Law of Segregation
states that the 2 alleles for a heritable character segregate (separate from each other) during gamete formation (meiosis) and end up in different gametes
- thus, an egg or sperm gets only ONE of the 2 alleles that are present in the somatic cells of an organism
If an organism has identical alleles for a particular character, then that allele is present in all gametes. What will the offspring look like?
If different alleles are present, what will the gametes have?
Because it is the only allele that can be passed on to offspring, the offspring will always look like their parents
- explains true-breeding plants
If different alleles are present, as in the F1 hybrids, then 50% of the gametes receive the dominant allele and 50% receive the recessive allele
An organism that has two identical alleles for a character (gene)
- is said to be homozygous for that character
Homozygous plants breed true, why?
because all of their gametes contain the same allele (ex: either P or p)
If we cross dominant homozygotes with recessive homozygotes, every offspring will have __ _______ ______
2 different alleles (Pp in F1 hybrids of pea experiment)
An organism that has two different alleles for a trait (gene)
- not true-breeding
Law of segregation states that 2 alleles ______ from each other at the time of _____ _____ and they end up with...
1/2 the gametes having one allele and 1/2 having the other allele
A punnet square shows
all of the possible combinations of alleles from the parents
Mendel's segregation model accounts for the...
3:1 ratio he observed in the F2 generation of monohybrid crosses
a diagram for predicting the results of a genetic cross between individuals of known genetic makeup
individuals that are heterozygous for one character in a cross
- a cross between such heterozygotes is a Monohybrid Cross
a cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait
- unknown genotype can be determined from that of the offspring
law of independent assortment
states that each pair of alleles segregates independently of any other pair of alleles during gamete formation
genes are packaged into gametes in all possible allelic combinations as long as....
each gamete has one allele for each gene
Law of Independent Assortment applies only to genes (allele pairs) located on ______ ______ ______ or to genes that are _____ ____ _____ on the _______ chromosome
different non homologous chromosomes
very far apart
- Genes located near each other on the same chromosome tend to be inherited together
Dependent Assortment Hypothesis
if the hybrids must transmit their alleles in the same combinations in which the alleles were inherited from the P generation, then the F1 hybrids will produce only 2 classes of gametes " YR and yr
- predicts phenotypic ratio of the F2 generation will be 3:1, just as in a monohybrid cross
a cross between F1 dihybrids (differs in 2 characters)
Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations:
1. when alleles are not completely dominant or recessive
2. when a gene has more than 2 alleles
3. when a gene produces multiple phenotypes
Complete Dominance occurs when _____ of the ______ and ________ ______ are identical
heterozygote and dominant homozygote
(Mendel's classic pea crosses)
the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties
- neither allele is completely dominant
2 dominant alleles affect the phenotype in separate, distinguishable ways
- heterozygotes: both alleles are present and both phenotypes are exhibited
Whether alleles appear to be completely dominant, incompletely dominant, or codominant depends on what?
the level at which phenotype is analyzed
genes that exist in populations in more than 2 allelic forms
example of multiple alleles : ABO blood type
the __ phenotypes of the ABO blood group are determined by __ alleles for the enzyme (I) that attaches __ or __ _______ to RBC's.
- enzyme encoded by the IA allele adds the __ _________
- enzyme encoded by the IB allele adds the __ ______
- enzyme encoded by the i allele adds ____
* _______ _______ between IA and i & IB and i
* ________ between IA and IB
A or B carbohydrates
Codominance - both are expressed
A single gene having multiple effects on an individuals phenotype
pleiotropic alleles are responsible for the multiple symptoms of certain ______ diseases such as ____ ____ and ___-_____ ______.
In these diseases, multiple symptoms can be traced back to ___ _____ _____.
cystic fibrosis and sickle-cell disease
one defective allele
the phenotypic expression of a gene at one locus alters the phenotypic expression of a gene at a second locus
example of epistasis:
In mice and other mammals, coat color depends on __ genes
- one gene determines the _____ ______ (what are the alleles?)
- the other gene (what are the alleles?) determines...
pigment colour (B for black and b for brown)
whether or not pigment will be deposited in the hair (C for colour and c for no colour)
- gene for pigment deposition (C/c) is said to be EPISTATIC to the gene that codes for black or brown pigment (B/b)
multiple genes independently affect a single trait
- the phenotype is an accumulation of contributions by multiple genes
EX: skin colour in humans
those that vary in the population along a continuum
quantitative variation usually indicated _______ _____
- an additive effect of 2 or more genes on a single phenotype
a genotype generally is not associated with a rigidly defined phenotype, but with a range of _______ ____ due to _______ _______
phenotypic range (norms of reaction) is broadest for _____ ____
multifactorial is when many ____, both ____ and _____, collectively influence the ______.
- _______ _______ are multifactorial
factors, both genetic and environmental
- polygenic characters
example of environmental impact on phenotype
The coat color in Himalayan rabbits and Siamese cats is affected by temperature
- an allele produces an enzyme that allows pigment production only at temperatures below 30 degrees Celsius
physical characteristics of an organism
- all aspects of its physical appearance, internal anatomy, physiology, and behavior
genetic makeup of an organism
- gene's impact on phenotype is affected by other genes and by environment
many human traits follow...
Mendelian patterns of inheritance
Why are humans not good subjects for genetic research?
- generation time is too long
- parents produce relatively few offspring
- breeding experiments are unacceptable/unethical
___________ is a family tree that describes the interrelationships of parents and children across generations
Inheritance patterns of particular traits can be traced and described using ______.
They can also be used to make _______ about future offspring
a trait determined by a gene on the sex chromosome is said to be ______-______
In Drosophila (genus of flies) sex is determined by the....
number of copies of the X chromosome
Mendelian traits assort _______ because chromosomes assort ________
genes on X chromosomes - expressed in both Males and Females
Y chromosome - very small and haas less genes - will only be expressed in males
Traits influenced by a gene found on any of the autosomes (non-sex chromosomes)
genes located relatively far apart on a chromosome are more likely to ____ ___ than genes located closer together
frequency of crossings can be used to construct a ______ _____.
- measures distance between genes in terms of _______ _______
________ relationship between distance of genes and frequency of crossing over
An error in meiosis 1 or 2 in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other.
_______ ______ identifies parents at risk of producing children with genetic defects and assesses state of early embryos
high risk pregnancies
couples with recessive alleles
mothers older than 35
amniocentesis and chorionic villus sampling
can indicate whether a suspected genetic disorder is present in a fetus
(14th to 16th week)
needle is inserted into amniotic cavity, and a sample of amniotic fluid is withdrawn into syringe
- amniotic fluid contains some free cells derived from the fetus
- fetal cells are grown in a culture, and their karyotype and many of their metabolic functions are examined
chorionic villus sampling (CVS)
(8th to 10th week)
physician inserts tube through cervix into uterus and suctions out a tiny sample of tissue from chorion (membranous part of the placenta that nourishes fetus)
- cells of chorionic villi have same genotype and DNA sequence as fetus
- cells proliferate rapidly enough to allow karyotyping immediately
systems in which you are manipulating the DNA of the organism
- manipulation of organisms or their components to make useful products
In many eukaryotic genomes, ______-________ genes occupy only a small portion of the chromosomal DNA, the rest being ________ ________ ______
noncoding nucleotide sequences
distinctions between a gene and the surrounding DNA are subtle, consisting only of...
differences in nucleotide sequence
DNA cloning are methods for preparing ____-______ _____ of DNA in multiple _____ _____
plasmids are small ______ _____ molecules that _________ separately from the _____ chromosome
- has only a small # of genes
Recombinant DNA molecule
a molecule containing DNA from two different sources
- very often different species
A bacterium that contains a plasmid which has been inserted with DNA from a different source
- This cell reproduces through repeated cell divisions to form a clone of cells.
clone of cells
a population of genetically identical cells
the production of multiple copies of a single gene
Gene cloning is useful for 2 basic purposes
1. make copies (amplify) a particular gene
2. produce a protein product from it
________ ______ are DNA molecules that can carry foreign DNA into a host cell and be replicated there
Restriction endonucleases = restriction enzymes
enzymes that can cleave DNA at specific sites
- allow the creation of recombinant DNA molecules
Restriction enzymes recognize DNA sequences termed _______ _____
- Specific site where a restriction enzyme cuts the DNA
- palindromic sequences read the same on either strand from 5' to 3'
_______ _______ is a DNA segment that results from the cutting of DNA by a restriction enzyme.
- all copies of a given DNA molecule always yield the same set of restriction fragments when exposed to the same restriction enzyme
restriction enzymes cleave the _____-_____ _______ in 2 DNA strands in a _____ manner that generates ______ _______
overhanging complementary ends that result from a cut by a restriction enzyme
- fragments cut by the same enzyme can be paired
______ ______ joins the 2 fragments cut by a ______ ____ forming a stable ______ DNA molecule
sticky ends : short extensions form ______-______ base pairs with ______ sticky ends on any other DNA molecules cut with the ______ _____
genetically identical copy
Multiplication and isolation of a specific DNA sequence
(aka gene cloning)
propagation of DNA in a host cell requires a _____
stages of cloning (4)
1. DNA from 2 sources is isolated and cleaved with the SAME restriction endonuclease
2. the 2 types of DNA can pair at their sticky ends when mixed together (DNA ligase joins the segments)
3. Plasmids are inserted into bacterial cells by transformation
- bacterial cells reproduce and form clones
4. clones are screened for gene of interest (some cells won't have the foreign DNA)
_______ is the introduction of DNA from an outside source into a cell
______ has a region where you can cut the DNA with a restriction enzyme and bring in foreign DNA and put it there
the introduction of DNA into the nucleus of a cell by injection through a very fine needle.
- have a cell held by suction on a holding pipette
- injection pipette goes through plasma membrane and into nucleus to insert DNA (gene)
Infection by the Ti Plasmid
wherever it finds openings (stem/root) if infects that region, gets inside plant cell, and begins to grow there
- once inside, it transfers part of Ti Plasmid (T-DNA) from bacterial cell into plant cell
- T-DNA has genes that produce nitrogen metabolites which allow for growth
- this cell multiplies and forms a tumour in the plant
- gel (agarose or polyacrylamide) is subjected to an ______ _____
- the DNA (which is ________-_______) migrates towards the ______ ______
- the larger the DNA fragment, the _____ it will move through the gel matrix
- smaller fragments move ____ and cover ____ distance
- DNA is visualized using ______ ______
- samples move from _____ to ______
- larger DNA fragments are _____ _____ origin
- smaller DNA fragments are _____ ______ _____ origin
technique used to separate DNA fragments by size
- electrical field
- negatively-charged, positive pole
- faster, more
- fluorescent dyes
- negative to positive
- closer to
- farther away from
large collections of known DNA sequences
- a collection of DNA fragments from a specific source that has been inserted into host cells
represents an entire genome
represents only the expressed part of the genome
- not including non-coding regions or heterochromatin
- ONLY euchromatin and coding regions (genes that will be expressed into proteins)
complementary DNA (cDNA) is synthesized from ______ ______ using the enzyme _______ _______
_____ ______ is the process of determining the precise order of nucleotides within a DNA molecule
- a set of nested fragments is generated - end with known base
- separated by a high-resolution gel electrophoresis, resulting in a "ladder"
- sequence is read from bottom up
polymerase chain reaction (PCR)
3 step cycle that brings about a chain reaction that produces an exponentially growing population of identical DNA molecules
polymerase chain reaction steps
1. Denaturation = heat briefly to separate DNA into 2 strands
2. Annealing = cool to allow primers to form hydrogen bonds with ends of target sequence
3. Extension = Heat-stable DNA Polymerase adds nucleotides to the 3' end of each primer (extends in 5' to 3' direction)
= original small amount of DNA (target sequence) results in millions after PCR
Taq polymerase in PCR
heat-stable DNA polymerase
- heat-tolerant so it doesn't die or denature when the heat is high in oder to denature DNA (separate the strands)
- comes from bacterial species that lives in hot springs
very small infectious particle consisting of a nucleic acid surrounded by a protein coat and, in some cases, membranous envelope
Viruses are NOT ______ _____
- just chemical
- can ONLY replicate inside a host cell
Viruses and Cancer
1. triggering expression of oncogenes
2. disrupting tumour-suppressor genes
genes responsible for cancer formation
- induces repeated division of a cell
- in normal form they are protooncogenes
___________ _______ ________ are genes in all cells that identify defective regions in DNA
Tumour suppressor genes
- any cell that has a defective region, it does not allow cell to multiply
viruses lead a _______ life between life-forms and chemicals
viruses possess only a portion of the properties of organisms
1. segments of DNA or RNA wrapped in a protein coat
2. must reproduce within cells
* cannot have their own existence - need to be inside a host cell
nature of viruses
- no classification system available
- viruses are NOT cells
- viruses replicate ONLY IN host cells
- all viruses have same basic structure
________ is used for recognition of what host cell it can infect (viruses)
capsid is a ______ ______ that encloses ______ _____
capsid is built from protein subunits called ________
surrounds the capsids of influenza viruses and many other viruses found in animals
- derived from host cell's membrane
- contain combo of viral and host cell molecules
A virus that infects bacteria
- also called a phage.
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