Bio 101 Exam 2 Flashcards
(114 cards)
0
Q
When nucleotides assemble, what do they form?
A
A sugar phosphate backbone
1
Q
Nucleotides
A
- one of four nitrogenous bases attached to deoxyribose (sugar + base= nucleoside)
- phosphate group attached to the 5’ C of deoxyribose (nucleoside+ PO4 group= nucleotide)
2
Q
How is DNA synthesized?
A
- 5’ PO4 of one nucleotide attaches to 3’ OH of preceding nucleotide
- always synthesized 5’ to 3’
3
Q
Nitrogenous bases
A
- adenine
- thymine
- guanine
- cytosine
- c and g and a and t always paired together
- c and g joined by 3 hydrogen bonds
- a and t 2 hydrogen bonds
4
Q
How is DNA polymerized?
A
- Into complementary antiparallel strands
- must be antiparallel to form hydrogen binds btwn bases
- parallel would repel each other
5
Q
DNA forms what shape?
A
Double helix
6
Q
What purpose does organizing and compacting DNA serve?
A
- fits large DNA molecules into tiny space
- stabilizes and protects DNA molecules
- allows for condensation during cell division
- helps regulate gene transcription
7
Q
How is DNA condensed?
A
- through various DNA- protein interactions
- eukaryotic DNA condensed into chromatin
8
Q
Steps in condensing DNA
A
Step 1: beads on a string (wrap around each histone protein )
Step 2: solenoid (beads on string twisted together)
Step 3: form chromosome
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Q
Chromosome structure
A
- chromosomes are divided into segments by the centromere
- the p (petit) arm is the short one
- the q arm is the long one - position of centromere determines the lengths of the arms
10
Q
Karyotypes
A
- a graphic display of all the chromosomes
- specific dyes are used to create banding patterns on the chromosomes
- Giemsa banding is the standard for human chromosomes - 22 pairs in humans
11
Q
Why is DNA capable of replication?
A
-because the hereditary factor through which traits are transmitted, so has to have a mechanism by which it can store information and be copied
12
Q
How can DNA store and replicate information?
A
- can store through the arrangement of the 4 nitrogenous bases
- can replicate itself due to complementary antiparallel structure
- 3 methods replication can occur via
- semiconservative
- conservative
- dispersive
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Q
Semiconservative replication
A
- double helix separates into two separate strands
- replicate other half of strand for each
- each double helix now contains one old strand and one new one
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Q
Conservative replication
A
- still split into two strands
- however final product is two old strands together and two new strands together
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Q
Dispersive replication
A
- shatter double helix into pieces
- each strand is part old and part new
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Q
Benefits of semiconservative
A
- parental DNA remains intact during replication
- each new DNA molecule has one original strand and one new strand
- preserve integrity of DNA and allow for proof reading to reduce risk of errors
17
Q
How does semi conservative replication occur?
A
- helicase unwinds the double helix and exposes bases
- DNA polymerase binds to single strand of DNA and adds new strand using old strand as template
- has ability to proofread
- sees incorrect pairing, removes incorrect base
18
Q
How is DNA polymerized? (Steps)
A
- dATP recruited by DNA polymerase
- catalyzed by polymerase, using thymine in the template strand, dATP attacks the 3’ OH of cytosine on the new strand
- polymerase catalyzed the formation of a new phosphorites term bond, attaching adenine to the 3’ end of new strand
19
Q
How is DNA replicated?
A
Through cell cycle
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Q
Interphase
A
- any stage not mitosis
- divided into three stages
- G1
- S
- G2
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Q
G1
A
-Cell grows and prepares for DNA replication
-
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Q
S
A
-DNA replicated
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Q
G2
A
-cell continues to grow, prepares to divide (now has two chromosomes)
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Mitosis
- replicated DNA is distributed btwn two identical cells
- divided into four stages
- prophase
- metaphase
- anaphase
- Telophase
- cytokinesis (not technically part of mitosis)
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Prophase
- chromatin condenses into chromosomes
- sister chromatids are connected at the centromere
- nuclear envelope breaks down
- nucleolus disappears
- centrosomes migrate to opposite poles
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Prometaphase
- nuclear membrane continues to break down
- microtubules attach to chromosomes
- micro tubules move chromosomes to center of cell
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Metaphase
-chromosomes align randomly along the metaphase plate with the aid of mitotic spindle
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Telophase
- two daughter cells are produced by mitosis
| - each is Aa. Bb following sister chromatid separation to form daughter chromosomes
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Checkpoints to control cell cycle
1st checkpoint: btwn G1 and S. Makes sure cell is ready for DNA replication
2nd checkpoint: btwn S and G2. Checks for errors in DNA replication
3rd checkpoint: at metaphase. Checks to see if the chromosomes are aligned and attached to a microtubule
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Cyclins and CDK
- CDK levels remain constant
- cyclin levels vary throughout cell cycle
- cyclin E: 1st checkpt
- cyclin A: 2nd checkpt
- cyclin B: 3rd checkpt
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Cancer
- caused by a broken regulatory system
- uncontrolled cell growth (results in a tumor)
- has the potential to invade other parts of the body (metastasis)
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Metastasis
-occurs when the abnormal cells of the primary tumor travel to a new location in the body
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Proto-oncogenes
- gene that controls cell cycle
| - tells cell it's time to divide
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Oncogenes
- mutated proto-oncogenes
- mutations that cause increased activity lead to cancer
- MYC (most common oncogene)
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Tumor suppressors
- gene that says cell cycle should not go forward because we have a problem
- controls cell growth and division
- mutations lead to cancer
- P53: tumor suppressor. Of cell is beyond repair, tells it to comment apoptosis
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Apoptosis
Cell suicide
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Chemotherapy
- chemical agent used to treat abnormal cell growth
- typically targets all rapidly divid ping cells (affects intestinal cells, hair follicles, bone marrow, etc)
- targeted therapy
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Radiation therapy
- if tumor is close to the surface of skin
- targeted beams if radiation are used to kill cancerous cells
- radiation damages DNA of cells cause their death
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Microtubules
- hollow cylinders made of protein called tubulin
- microtubule is anchored at end
- have roles in cell structure, serve as roadway for transport, and are important for chromosome separation
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Microtubule organizing center
(MTOC)
•In non-dividing cells, microtubules are anchored to MTOC called centrosome (13)
•Made of two hollow tubes of microtubules at right angles to one another (centrioles)
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Preformationism
- William Hawey, Jan Swammerdam, Marcello Malpighi
- 1600-1900 AD
- a tiny preformed organism (homunculus) arises from the sperm or egg
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Epigenesis
- Kasper Friedrich Wolff
- 1759
- showed that embryonic layers of cells give rise to plant and animal tissues (don't start off preformed)
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Soft inheritance
- Jean-Baptiste Lamark
- 1800 AD
- inherit characters from parents based on character the parents develop throughout their life
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Pangenesis
- Charles Darwin
- 1868 AD
- inheritance particles (gemmules) are shed from all cells in the body and collect in reproductive cells
- like soft inheritance, believed acquired traits would be transmitted
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Germplasm
- Augustus Weisman
- 1892 AD
- only the germ cells contribute to inheritance
- ruled out possibility of acquired inheritance
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Mendelian Genetics
- Gregor Mendel
- 1866AD
- work was largely ignored until 1900 AD
- showed that the units of heredity came in parts, one from the egg and one from the sperm
- father of modern genetics
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Dominant phenotype
The trait that is expressed at the expense of its paired partner
-only one copy needed to be present for the trait to be expressed
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Recessive phenotype
-the trait expressed only when both copies are present
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Heterozygous
- display dominant phenotype
| - two different alleles Gg, Gg
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Homozygous
-same allele GG, gg
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Dominant and recessive traits
1:2:1 genotype ratio
3:1 phenotype ratio
Each trait is independent of the other ones
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Pedigrees
Family trees showing the occurrence of phenotypes between generations
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Autosomal Dominant Inheritance
- affected individuals must have at least one affected parent
- both sexes are affected in high numbers
- either sex can transmit inheritance
- in crosses where one parent is affected, about 50% of the offspring have the phenotype
- two unaffected parents will not have an affected offspring
- two affected parents may produce unaffected offspring
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Autosomal Recessive Inheritance
- affected individuals are often born from unaffected parents
- if a parent is affected, the chance of transmitting the phenotype depends on the other parents genotype
- if both parents are affected, the children will be affected equally
- the disease is not usually seen in each generation but if an affected child is produced by unaffected parents, the risk to subsequent children is 1/4
- if the phenotype is rare it is likely that unaffected children are related to each other
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Meiosis
- produces 4 haploid(half the normal number of chromosomes) gametes
- divided into meiosis I and meiosis II
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Interphase I
-S phase, chromosomes replicate
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Prophase I
- Homologous chromosomes pair together
| - physically exchange sections of DNA by "crossing over"
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Synapsis
-Pairing of homologs (homologous chromosomes) to form tetrad
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Metaphase I
-tetrads line up at metaphase plate
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Anaphase I
- pairs of homologous chromosomes are pulled to opposite poles
- sister chromatids stay together
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Telophase I and cytokinesis
- two haploid cells form
| - chromosomes are still double
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Prophase II
-prepare to divide again
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Metaphase II
-sister chromatids align along equator of a haploid cell
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Anaphase II
-Sister chromatids separate
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Telophase II
- nuclear envelope forms around each set of chromosomes resulting in 4 haploid cells
- each contain single chromosomes
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Central Dogma of molecular biology
DNA replication
RNA transcription
Protein translation
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RNA
- RNA structure is similar to DNA
- 2 key differences
1. RNA uses ribose sugar, DNA uses deoxyribose
2. RNA replaces thymine with uracil
- RNA polymerized similar to DNA except uses RNA polymerase
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Transcription
- process by which a gene is copied into a complementary strand of mRNA
- synthesized 5' to 3'
- mRNA transcript is complement of DNA template strand
- transcript is identical to DNA coding strand (except uracil has replaced thymine
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Translation
* DNA stores information for making proteins
* mRNA carries the instructions to the ribosomes (where the protein can be assembled)
* process of using the nucleotide sequence of an mRNA to synthesize amino acids to form a protein
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Types of RNA in translation
- mRNA
- tRNA
- rRNA
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mRNA
-template that brings the recipe for the protein to the ribosome
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tRNA
-translates the message in the mRNA into an amino acid sequence
-add the amino acid specified by a given codon
-Complementary bases pair with codon through a region called the anti-codon
•3’ end of tRNA is attached to a specific amino acid
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rRNA
associates with proteins to form the machinery needed to assemble the proteins
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How to translate mRNA
- read it in groups of 3 nucleotides called codons
- each codon corresponds to a specific amino acid (called genetic code)
- Methionine is the start codon (AUG)
- UAA, UAG, or UGA do not code for an amino acid and signal translation to stop
- Sequence from start codon to stop codon is called the open reading frame (ORF)
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Ribosomes
* bind mRNA and recognize the start codon (AUG)
* provide an environment that facilitates the proper binding of mRNA and tRNA
* serve as the catalyst for peptide bond formation between the amino acids
* highly conserved through evolution and are structurally similar in all organisms
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All cells in an organism....
- Are distinctly different
- produce diff things, look different
- contain exact same DNA
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Activators and repressors
- Can regulate which genes are turned on and which proteins are being made
- regulate at DNA
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Transcriptional activators
bind to DNA elements to facilitate activation of the target gene
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Transcriptional repressors
-bind to DNA elements to facilitate repression of target genes
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What are proteins encoded by and responsible for?
Genes, traits
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Incomplete dominance
•Neither trait is truly recessive or dominant causing a “mixture” of the traits when crossed
Ex. Red flowers + white flowers =pink flowers
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Codominance
```
When heterozygotes express products from both alleles leading to a different phenotype than either homozygote
Blood types
Type A
Type B
Type AB
Type O
```
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Epistasis
•When the effects of one gene rely on the presence of other genes
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Sex determination
Sex determination is the biological and genetic processes that produce male and female characteristics
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Chromosomal sex
Chromosomal sex is the presence of chromosomes characteristic of each sex and are determined at fertilization
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Phenotypic sex
•Phenotypic sex is the internal and external characteristics of each sex resulting from differences in gene expression
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Sex determination in mammals
* In mammals, sex is determined by the presence or absence of a single gene called SRY
* SRY is a protein needed to turn on male-specific genes
* SRY is located on the Y chromosome
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Sex linked genes
* Traits that are controlled by genes located on the sex chromosomes
* X-linked dominant-trait only on x, dominant
* X-linked recessive
* Y-linked
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Sex influenced genes
•Traits are controlled by gene not located on sex chromosome but influenced by gender
BB m f bald
Bb m bald
bb
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Sex limited genes
•Trait is not controlled by genes located on sex chromosome but is limited to only one gender
Beards, horns
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Gene-environment interaction
* Occurs when the effect of the environment on an individual is dependent upon their genotype
* Or when the effect of gene expression on an individual is dependent on the environment
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Quantitative traits
•Complex traits controlled by numerous genes and factors
•Discrete traits – A or B; On or Off
•Continuous traits – traits fall within a range
Metabolism
IQ
Height
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Polygenes
* Height is controlled by 5 different genes
| * Each gene has 3 possible genotypes
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Additive genes
•Continuous traits arise from incremental contributions of numerous genes
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Threshold traits
•A trait has continuous variation but can still be categorized into discrete phenotypes
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Heritability
* The amount of phenotypic variance that is due to genetic factors
* Twins can be used to study heritability in humans
* Identical twins should have 100% same genes so any variance must be due to environment
* Fraternal twins should be 50% same genes so variance could be combination of genes and environment
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Gene therapy
* Gene therapy is the manipulation of an organisms genes to treat disease
* Can correct mutant gene
* Can knockout dysfunctional gene
* Can insert new gene
* Most promising for monogenic disorders and cancers
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Plasmids
A genetically modified organism can be engineered using genes cloned into these tools consisting of circular double stranded DNA
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How can we engineer genes?
•DNA is extremely large with the human genome consisting of 3 billion base pairs
•We need a way to isolate only the portions of the genome we are interested in
-plasmids
-restriction enzymes
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Restriction enzymes
Enzymes isolated from bacteria cut DNA at specific sites called restriction sites
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Point mutation
a change of a single nucleotide
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Silent mutation
No change in amino acid coded for
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Missense mutation
aa changes due to mutation
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Nonsense mutation
aa changes to stop codon
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Insertions or deletions
Bases are added or removed from sequence
| Typically results in a frame shift mutation
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Agents that mutate DNA are called
Mutagens
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Mutation
Changing of genetic code overtime
| DNA mutations occur spontaneously
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Embryonic stem cells
pluripotent cells often used in medical research
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Mesoderm
Middle layer
Muscles
Multipotent layer
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Endoderm
Internal layer
internal organs such as the stomach and pancreas
Multipotent layer
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Ectoderm
Outer
Skin
Neutrons
Multipotent
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Zygote
Totipotent
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Hox genes
This highly conserved family of genes is important in determining the body plan layout of an embryo
