Final Flashcards
Association of Genes and Chromosomes
Red eyes being the dominant phenotype (represented by “X^R”) and white eyes being the recessive phenotype (represented by “X^w”)
Sex Linked-Traits
o Sex-linked traits are those more frequent in either males or females
o They are usually associated with genes on either the X (X-linked) or Y (Y-linked) chromosomes
Mammal Sex chromosomes
X is large, with about 900 genes
Y is small, about 100 genes, highly degraded
During meiosis I, X and Y pair in a single region, the pseudoautosaomal region. The rest of the X/Y are very different from each other, and so do not align with each other.
Homozygous
X-X- shows recessive
Heterozygous
X+X- does not show trait
Hemizygous
X-Y shows recessive phenotype
X+Y does not show phenotype
X Chromosome inactivation
In females, only one of two X chromosomes express genes
Barr Body
One chromosome remains unwound and can express genes, the other is highly condensed
Gene-Linkage
Proximity of two or more genes one a chromosome can affect patterns of inheritance
Gene-Linkage of fruit flies
o The two more common offspring classes represent the parental gametes (alleles in combination found in the parents chromosomes)
o The two less common offspring classes represent transmission of recombinant gametes (chromosomes result from crossing over between homologous chromosomes during meiosis in the F1 females)
Aneuploidy
An incomplete set of chromosomes
Trisomy
One extra chromosome
Monosomy
Missing one chromosome
Nondisjunction
failure of homologous chromosomes (meiosis I) or sister chromatids (meiosis II and mitosis) to separate at anaphase
Down Syndrome
Extra copy of Chromosome 21, Trisonomy 21
“Common” sex chromosome Aneuploids
- XXY: Klinefelter syndrome
- XYY: about 1 in 1000 males, no apparent complications
- XXX: triple X females, no apparent complications
- XO: Turner’s syndrome, the only known viable monosomy in humans
Chromatin
Complex of DNA & proteins
Histones
Primary Proteins
Form octamers (groups of eight) called Nucleosomes
DNA winds around each nucleosome twice, about 150 bp
Euchromatin
Interphase chromosomes are usually in unpacked state
Heterochromatin
Highly Packed State
Inaccessible and so, not expressed
Chargaff’s rule
The rule that in DNA there is an equal amount of A&T and G&C
3 model’s of DNA replication
Conservative, semiconservative, dispersive
Conservative model
This model proposes that the original DNA molecule remains completely intact and a completely new DNA molecule is formed from scratch, essentially creating one “old” DNA and one “new” DNA
Semi-Conservative model
This model suggests that each strand of the original DNA molecule serves as a template to create a new complementary strand, resulting in two new DNA molecules, each containing one strand from the original DNA.
Dispersive model
This model proposes that the original DNA strands become fragmented, and the new DNA is created by mixing pieces of the old strands with new pieces, resulting in a DNA molecule with segments of both old and new DNA interspersed throughout.
Meselson & Stahl 1953
Conducted an experiment that provided conclusive evidence that DNA replicates semi-conservatively
Meselson & Stahl experiment
Tested bacteria using heavy isotope of nitrogen, 15N (normally 14N is lighter)
Origin of Replication
At origin of replication, DNA strands disassociate forming a replication bubble. The regions on the flanking ends are the replication forks.
DNA Replication Prokaryote vs Eukaryotes
o In prokaryotes, with only a single circular chromosomes, there is just one origin of replication
o In eukaryotes, with several to many linear chromosomes, there are many origins if replication
Helicases
Untwist DNA double-helix and separate DNA strands
Single-stranded binding proteins (SSBDs)
Bind and stabilize single-stranded DNA (ssDNA).
Topoisomerases
Relieve tensional strain of DNA molecule by breaking, swiveling, and rejoining DNA.
Primase
Add short RNA primers (~5-10 nucleotides), to provide 3’ end for DNA polymerase to add nucleotides to
DNA polymerase III
Adds nucleotides to RNA primers
DNA polymerase I
Replaces RNA primers with DNA nucleotides
DNA ligase
Joins DNA backbone of DNA strands from replaced primer and Okazaki fragments
Okazaki fragments
Short DNA sequences that are created during DNA replication when the lagging strand is synthesized discontinuously
Gene Expression
The process by which information encoded in DNA produces functional proteins.
DNA > RNA > Protein
Transcription
synthesis of messenger RNA (mRNA) from region in DNA
Translation
synthesis of polypeptide using mRNA through action of ribosomes
Gene Expression Prokaryotes vs Eukaryotes
In prokaryotes, gene expression is primarily regulated at the transcriptional level and occurs almost simultaneously with translation in the cytoplasm
In eukaryotes, gene expression is regulated at multiple levels including transcription, RNA processing, and translation
3 Stop Codon
UAG, UAA, and UGA
1 Stop Codon
AUG
Redundancy
Multiple triplets can encode the same amino acid
Coding Strand
Also called nontemplate strand, sequence that is the same as what will form the messenger RNA (mRNA).
Template Strand
used to synthesize its complement into an mRNA molecule.
Initiation
Proteins called transcription factors mediate binding of RNA polymerase II to the promotor region upstream of coding sequence.
RNA polymerase II form initiation complex
requires a specific sequence called a TATA box in the promotor region for transcription initiation to be initiated.
Elongation
RNA polymerase travels down template strand and synthesizes mRNA molecule
Termination
In eukaryotes, RNA transcribes a polyadenylation sequence (~10-35 nucleotides) and then the RNA molecule is released (produces pre-mRNA)
pre-mRNA
- 5’ cap: a modified nucleotide, guanosine triphosphate (GTP) is added to the 5’ end of RNA molecule
- 3’ polyA tail: series of Adenines (~50-250 nucleotides) are added to the 3’ end of the pre-mRNA
Introns vs Exons
the mRNA coding region comprised of exons, which code for amino acids, and introns, which do not code for amino acids. Introns must be removed for successful translation
Spliceosomes
A complex of proteins and RNA molecules that bind sequences at intron-exon junctions
Components of translation
- Mature mRNA
- Ribosomes
- Transfer RNAs (tRNA)
Direction mRNA is read
mRNA read 5’ 3’ by the ribosome
Transfer RNA
Ribosomes
- Two subunits, large and small
- These subunits join after the small subunit has associated with an mRNA
- Ribosome has four binding sites: 1 for mRNA (on small subunit) 3 for tRNAs (on large subunit
Initiation
5’ end of mRNA binds to mRNA binding site of small ribosomal subunit
Elongation
tRNA shifts from A > P site, then P > E site > uncharged tRNA exits ribosome
Termination
- A site accepts “release factor”, a protein that incorporates H2O instead of an amino acid
- This release the polypeptide, terminating translation, and the ribosome disassembles
Mutation
When there is a change in the DNA of a cell
Silent Mutation
change in DNA does not effect which amino acid is encoded
* This happens because of the redundancy in the genetic code
Missense Mutation
change in DNA that change the amino acid encoded. \
* This produces a single amino acid change in there resulting polypeptide
Nonsense Mutation
change in DNA produces a stop codon
* This truncates the polypeptide translated, and usually has a severe effect on the functionality of the protein
Insertions/deletion
- Change in the length of the DNA, thus mRNA
- If not in a multiple of three (a codon), this changes the reading frame, thus the identity of all amino acids downstream of the indel
Respiratory System of vertebrates
- All organisms must acquire nutrients and other resources from their environment
- For small, simple substances like O2 and CO2, this happens by diffusion through the plasma membrane
Lungs
o Infoldings of the body surface, divided into numerous small pockets
o Shared (nearly) all terrestrial vertebrates
o Pathway of air intake
Pathway of air pressure
o Inhalation: Contraction of rib muscles and diaphragm
o Pathway through nasal and oral cavity
o Past pharynx and larynx
o Down trachea to bronchi
o To bronchioles
o To alveoli
Gas exchange to capillaries by diffusion
Respiratory system cleaning
o Cilia & mucus line epithelium of air pathway to move particles up towards the oral/nasal cavity.
o Alveoli cells lack cilia, so cannot clean themselves
