BIO202 EXAM 3 Flashcards
What is interphase?
When cells are not dividing
What is mitosis?
The separation of duplicated chromosomes
What are the 4 phases of the cell cycle?
G1, S, G2, and M phase
Which of the stages of the cell cycle make up “interphase”?
G1, S, and G2
Does Mitosis take place in prokaryotes?
No, they only contain 1 chromosome and are only 1 cell.
In G1 phase….
each chromosome contains 1 DNA molecule
In S phase…
DNA molecules replicate, 2 identical copies are formed, and stay attached to one another.
Kinetichore MT
attach to chromatids
non-kinetochore MTs
go from centrosome to metaphase plate and overlap
What’s the metaphase plate?
The center of the cell
What are the 5 phases of mitosis?
Prophase, Prometaphase, metaphase, anaphase, and telophase.
What is prophase?
The first stage of mitosis. This is where the chromosomes condense into visible chromosomes and then microtubule form in the cytoplasm between centriole pairs. It lengthens as the microtubules grow.
What is prometaphase?
The second stage of mitosis. This is where the nuclear envelope fragments, the mitotic spindle invades the nucleus, and microtubules bind chromatids at kinetochores.
What is metaphase?
The third stage of mitosis. This is where centrosomes are at the opposite ends of the cell. The chromosomes that are attached to microtubules line up at the metaphase plate.
What is anaphase?
The 4th stage of mitosis. This is where sister chromatids separate and are pulled toward opposite poles. Kinetichore MTs shorten as tubulin dimers are removed.
What is telophase?
The fifth and final phase of mitosis. This is where the nuclear envelope reforms and chromosomes partly unfold.
What stage do non-dividing cells remain in?
G0 phase
What are checkpoints?
Places in the cell cycle where it stops unless it is given the “go ahead” signal
Where are the major checkpoints?
The G1, G2, and M phases
What happens if a cell does not get the “go ahead” signal at a checkpoint?
It enters G0 phase
G1 checkpoint
The most important checkpoint. It is called the restriction point. If a cell gets passed the restriction point, it typically completes the cell cycle.
What’s beneficial about leaving the cell cycle at the restriction point?
It ensures that the cell has the correct amount of DNA
cdk’s
(Cyclin-dependent kinases.) Provide cell cycle signals by phosphorylating other proteins. Each cdk regulates a different step. They’re inactive alone but active when bound to a cyclin protein
Which cyclin acts at the G2 checkpoint?
MPF
PDGF
Platelet-derived growth factor
asexual reproduction
offspring have the same DNA as parents (they’re identical)
sexual reproduction
2 parents both contribute DNA to offspring
What process makes sure in sexual reproduction, the offspring don’t have double the amount of DNA they should have?
meiosis
somatic cells
all cells except sperm and egg cells
chromosomes of human somatic cells
22 pairs of homologous chromosomes + 2 sex chromosomes
haploid number
n = number of chromosomes/cell in gametes
diploid number
2n = the number of chromosomes in somatic cells
meiosis
The formation of haploid cells from diploid cells. (The formation of eggs and sperm with only 1 chromosome of each pair.
basic steps of meiosis
1 round of DNA replication and 2 rounds of cell division (meiosis I and meiosis II)
What happens in interphase I of meiosis?
DNA is duplicated in the S phase and sister chromatids stay attached. Centrosome, centrioles duplicate
What happens in prophase I on meiosis?
The meiotic spindle forms. The structure of the spindle is the same in mitosis, meiosis 1 and meiosis II.
prophase I of meiosis
Chromosomes attach to the spindle. Homologous chromosomes attach to each other in a process called synapsis. Then, homologous chromosomes break and rejoin at equivalent positions. This is called crossing over.
2x2 sister chromosomes is called a
tetrad or bivalent
chiasma
sites of crossing over
chromosomes that have crossed over are called
recombinant chromosomes
Metaphase I of meiosis
Chromosomes line up at the metaphase plate. The homologous chromosomes stay attached. The two chromosomes of the pair are linked to opposite spindle poles.
Anaphase I of meiosis
Homologous chromosomes separate and sister chromatids stay attached
Telophase I of meiosis
Same events as in telophase of mitosis. Nuclei reform.
Cytokinesis of meiosis
The same as mitosis
Meiosis I
Reductional division because each daughter cell has only one chromosome of each pair
Interkinesis
The time between meiosis I and meiosis II
What happens between Meiosis II
Centrioles and centrosomes are replicated but DNA is not.
Meiosis II
Almost the same as mitosis
Prophase II
Spindle forms and chromosomes attach to it
Metaphase II
Sister chromatids attach to opposite poles of the spindle
Anaphase II
sister chromatids are separated
Telophase II
Same as mitosis; nuclei form
DNA
Stores and transmits hereditary information. It codes for protein.
Gene
DNA that specifies (codes for) amino acids in 1 protein
Homologous chromosomes
They’re almost identical. They have the same genes that may have slight changes
Allele
Different versions of the same gene
What causes variation between individuals?
Different forms of the same proteins coded for by different alleles of the same genes. They cause variation between individuals
Homozygous (for a gene)
having the same allele on both chromosomes of a pair
Heterozygous (for a gene)
having different alleles on the two chromosomes
Heredity
Transmission of different alleles between generations by meiosis and sexual reproduction
Genetics
The study of heredity and how heredity variation is passed down through generations
Mendel
discovered laws of inheritance using peas before genes and chromosomes were known
character
a heritable feature (e.g. flower color)
trait
one variant of a character (e.g. purple or white flowers)
Genetic cross
controlled mating of 2 organisms
What are “heritable factors” that Mendel postulated?
genes
genotype
what alleles an individual has
Phenotype
appearance
Law of independent assortment
different characters are inherited independently
Alleles of genes on nonhomologous chromosomes assort independently during gamete formation
An easier way of predicting outcomes of a genetic cross other than using Punnett squares
Calculate results for each character independently and then multiply
Predict the possible results for a het. x. het. cross (Aa x Aa)
1/4 AA
1/2 Aa
1/4 aa
Predict the possible results for a hom. x. het. cross (AA x Aa)
1/2 AA
1/2 Aa
AaBbCc x AABbCC: Chance of AaBBCC
1/16
How do you determine the chance of a desired phenotype?
Figure the chance of each genotype that fits the bill and then add the probabilities
Co-dominance
two alleles both have effects
Multiple alleles
more than 2 versions of a gene and its protein
epistasis
1 gene affects the expression of another
Polygenic inheritance
many genes contribute to phenotype
Pleiotropy
1 gene has several effects on phenotype
monohybrid cross
crossing two individuals each heterozygous for one character
Law of segregation
The two alleles for each gene separate during gamete formation. Organisms have 2 copies of each heritable factor but each gamete has only one copy.
locus
The position of a gene on a chromosome
Linked genes
are on the same pair of homologous chromosomes
wild type
normal appearance
mutant
abnormal phenotype
Unequal numbers in a dihybrid x double recessive test cross shows that
two genes are linked
Smaller numbers of offspring are always
recombinants
recombination frequency definition
how often recombination occurs between 2 genes
Recombination frequency is ____ when genes are close together.
Low
Recombination frequency is ___ when genes are far apart.
High
recombination frequency equation
(# of recombinants / total number of offspring) * 100
Genetic map
describes relative distances of genes along a chromosome
1% recombination frequency =
1 map unit
Autosomes
chromosomes in homologous pairs
Barr body
compact structure on the inside of the nuclear envelope
X-inactivation in female mammals
1 of the X chromosomes in each cell condenses into a Barr body early in dev
Which X chromosomes in inactivated?
Decision is random and independent in each cell in the embryo
Non-disjunction
failure of chromosomes to separate correctly in meiosis
Result of non-disjunction
daughter cells have abnormal number of chromosomes
Aneuploidy
having the wrong number of chromosomes
Trisomy
1 extra chromosome
Monosomy
missing 1 chromosome
Karyotype
Ordered display of chromosomes from a cell in mitosis. Reveals aneuploidy
Polyploidy
having extra sets of chromosomes
Why is aneuploidy often worse than polyploidy?
Chromosome balance is important.
Genomic imprinting
A type of inheritance pattern that doesn’t follow Mendel’s laws. During gamete formation, DNA in a few genes is modified.
Imprints
remain through life but imprints are erased and new imprints are made during gametogenesis
Genes in mitochondria and chloroplasts
These don’t exhibit Mendel’s laws. All mitochondria and chloroplast genes come from the mother.
hemizygous
Having only one copy of sex-linked genes
S cells
smooth cells that have a capsule to avoid the immune system and are pathogenic
R cells
rough cells that have no capsule. Host kills them and they are not pathogenic
Bacteriophage
virus that infects bacteria; turns bacteria into factories for making virus
What is implied when it is said that DNA replication is semi-conservative?
Each molecule has 1 old strand and 1 new strand
Leading strand
is made as a continuous strand
Lagging strand
synthesized in short fragments made in the 5’ to 3’ direction then joined later.
Okazaki fragments
Made 5’ to 3’. Start at the fork. DNA polymerase moves away from the fork
Primer
Short segment of RNA made by primase
DNA polymerase
adds dNTPs to the 3’ end of the primer
How are primers on Okazaki fragments replaced?
Another DNA polymerase replaces RNA with DNA
DNA ligase
joins the Okazaki fragments by forming a phosphodiester bond to link adjacent fragments into a continuous strand
Telomeres
(TTAGGG) A repeated short sequence in eukaryotic chromosomes they solve the issues faced when replicating DNA. In replication it can’t get all the way to the end of the strand so it shortens it a bit. Telomeres get shortened rather than losing genetic information.
Mismatch repair
DNA polymerase proofreads each dNTP after adding it and removes it if it’s incorrect
Excision repair
Repair of damaged DNA. A nuclease cuts out damaged region. Then, DNA polymerase and ligase fill in the gap
RNA polymerase II
The RNA pol. used to make mRNA
The direction of transcription is called
downstream
A promotor is _____ of its gene
upstream
First step of transcription
Binding of RNA pol. to a promoter
Transcription factors
Help RNA pols to bind to the promoter in eukaryotic cells
TATA box
one of the many transcription factors that first bind to DNA. It is located upstream f the start of transcription
Transcription initiation complex
RNA polymerase and other transcription factors
Initiation of transcription
DNA strands are separated only where RNA pol is bound. RNA pol starts an RNA strand at the transcription start point
Elongation phase of transcription
RNA pol. moves downstream (away from the promoter) RNA lengthens and DNA strands snap back together displacing RNA
Termination of transcription
RNA pol. falls off DNA at the end of the gene. RNA is released
Transcription terminator
A DNA sequence that signals the end of transcription in bacteria.
mRNA specific event
In eukaryotes, mRNA transcription continues through a polyadenyation signal, but RNA pol. II is released from the DNA shortly afterward
rRNA specific event
rRNA is made and assembled into ribosomes in the nucleolus
mRNA codes for
protein
mRNA processing occurs in the
nucleus. The initial transcription product is pre-mRNA, is converted to mRNA that leaves the nucleus
How is pre-mRNA modified in processing?
- Addition of 5’ cap
- Poly-A tail
- RNA splicing
Addition of 5’ cap and Poly-A tail
Stabilizes mRNA and facilitates ribosome attachment. Poly-A tail also enhances transport from the nucleus
RNA splicing
cut and paste removal of some sequences from pre-mRNA in the nucleus (only in eukaryotes)
Intron
A sequence that is removed
Exon
A sequence that remains and codes for protein
What are snRNPs?
(small nuclear ribonucleoproteins) made of RNA and proteins act in splicing
How do snRNPs act?
They bind to the pre-mRNA at the intron ends
spliceosomes
A complex formed when snRNPs bind other proteins. They bind both ends of an intron bringing them together then rejoins the ends of adjacent exons
Alternative RNA splicing
Some exons may be cut out as well as introns to give a different mRNA
tRNA
Folded by internal base pairing. Would look like a cloverleaf if flattened out. Interpret the genetic code
Anticodon in tRNA
binds codon
aminoacyl-tRNA synthetase
binds to a specific aa and a specific tRNA and covalently links them using energy from ATP hydrolysis
Ribosomes
sites of protein synthesis. Both contain RNA and protein. rRNA is the most abundant RNA in a cell
A site
aminoacyl-tRNA binding site
P site
peptidyl tRNA binding site
E site
Exit site
tRNA binding sites
Ribosomes binds mRNA near 5’ end. Ribosomes have 3 tRNA binding sites
Translation overview
aminoacyl-tRNAs bind to sequential codons and insert aa’s into protein
3 stages of translation
Initiation, elongation, and termination
Initiation of translation
Small ribosomal subunit binds mRNA at or near the 5’ end and also binds the initiator tRNA. Initiator tRNA binds to AUG in mRNA, (start codon) via its anticodon.
AUG
start codon
Initiation complex
Large ribosomal subunit bints to the initiator tRNA that is in the P site
Steps in elongation (translation)
- Codon regonition
- Peptide bond formation
- Translocation
Codon recognition
Incoming aminoacyl-tRNA binds to codon in A site
Peptide bond formation
Peptide bonds form between new aa and carboxyl end of growing chain. The chain is now linked to tRNA in the A site
Translocation
ribosomes moves along mRNA by the distance of 1 codon.
Result of translocation
tRNA that was in A site is now in P site, leaving A site free to restart cycle. tRNA that was in P site is now in E site and is released from ribosome
Termination
Occurs when a stop codon is present in mRNA
release factor
A protein that binds to a stop codon if it’s present in the A site. It releases a finished protein from the tRNA in the P site
Polyribosomes/polysome
many ribosomes on 1 mRNA
cytosolic proteins are made on
free ribosomes
Non-cytosolic proteins are made on
bound ribosome
