Flashcards in Ch 4: Genetics and Cellular Function Deck (22)
RNA Polymerase binds to PROMOTER region of a gene and separates the 2 strands of DNA double helix in the region of the gene to be transcribed. The Promoter region is a specific sequence of DNA nucleotides located near the beginning of the gene on the strand to be transcribed. Various transcription factors are present in the cell to help with this process.
2) RNA bases pair with DNA bases on the template strand of DNA. The template
strand is the strand being used for RNA synthesis. Pyrimidine bases (single ring)
always pair with Purine bases (double ring); Pyrimidines are cytosine, thymine,
and uracil, and Purines are adenine and guanine. Adenine pairs with thymine in
DNA and with uracil in RNA. Guanine and Cytosine always pair in DNA or
3) RNA polymerase links RNA bases to form a strand of mRNA.
4) RNA splicing removes INTRON (non-coding) regions of RNA. Splicing occurs in the nucleus and is performed by a complex of proteins and small nuclear RNA’sknown as a SPLICEOSOME. The spliceosome removes introns and joins
EXON (coding) regions to form a strand of mRNA. The exon regions code for
specific amino acids.
mRNA passes from the nucleus to the cytoplasm, where one end of the mRNA
binds to the small subunit of the ribosome, and associates with a START codon.
2) Free amino acids are linked to their corresponding tRNA’s by aminoacyl-tRNA
3) Pairing occurs between the tRNA ANTI-CODON and the mRNA CODON.
These are triplet bases that pair together.
4) The amino acid on the tRNA is linked by a PEPTIDE BOND to the end of the
growing polypeptide chain.
5) The tRNA that has been freed from its amino acid is released from the ribosome.
The ribosome moves one codon step along mRNA. And steps 3 to 5 repeat over and over until a STOP codon is reached. The completed protein is released from
the ribosome. The mRNA strand can return to the nucleus or go to another ribosome if more protein synthesis is required.
Protein Degradation Machinery
In the ubiquitin-proteasome pathway, energy from ATP is used to tag an unwanted protein with a chain of ubiquitins marking it for destruction. The protein is then hydrolyzed into small peptide fragments by the proteasome.
protein is damaged/made incorrectly and is tagged by ubiquitin to be destructed
Protein Secretion Mechanism
Protein made properly in the rough ER will receive a carbohydrate tag.
Tagged protein will enter the Golgi apparatus and travel down the saccules into the Golgi Vesicles.
Golgi vesicle will move toward lysosome and cell membrane; carbohydrate tag is cleaved off; and protein will leave cell via exocytosis.
if protein is made correctly; tagged by sugar to be secreted
Point mutations are the most common type of gene mutation. Also called a base-pair substitution, this type of mutation changes a single nucleotide base pair.
what are the 3 types of point mutations
gene mutation causes
Gene mutations are most commonly caused as a result of two types of occurrences.
*Environmental factors such as chemicals, radiation, and ultraviolet light from the sun can cause mutations.*
These mutagens alter DNA by changing nucleotide bases and can even change the shape of DNA. These changes result in errors in DNA replication and transcription.
Other mutations are caused by errors made during mitosis and meiosis. Common errors that occur during cell division can result in point mutations and frame shift mutations. Mutations during cell division can lead to replication errors which can result in the deletion of genes, translocation of portions of chromosomes, missing chromosomes, and extra copies of chromosomes.
According to the National Human Genome Institute, most all disease have some sort of genetic factor. These disorders can be caused by a mutation in a single gene, multiple gene mutations, combined gene mutation and environmental factors, or by chromosome mutation or damage.
examples of genetic disorders
-sickle cell anemia
sickle cell anemia
(A to T) of the β-globin gene, which results in glutamic acid being substituted by valine at position 6.
causes cell to have abnormal hemoglobin
THIS IS AN EX OF MISSENSE MUTATION
is a genetic disorder caused by the dysfunction of a protein that transports sodium and chloride across cell membranes. This protein is called the cystic fibrosis transmembrane conductance regulator (CFTR). Mutation of the CFTR gene gives rise to a protein that lets too much salt and not enough water into the cells, causing mucus to be become thick and sweat to become salty.
is a rare inherited disorder that progressively destroys nerve cells (neurons) in the brain and spinal cord.
Mutations in the HEXA gene cause Tay-Sachs disease. The HEXA gene provides instructions for making part of an enzyme called beta-hexosaminidase A, which plays a critical role in the brain and spinal cord. This enzyme is located in lysosomes, which are structures in cells that break down toxic substances and act as recycling centers. Within lysosomes, beta-hexosaminidase A helps break down a fatty substance called GM2 ganglioside.
Mutations in the HEXA gene disrupt the activity of beta-hexosaminidase A, which prevents the enzyme from breaking down GM2 ganglioside. As a result, this substance accumulates to toxic levels, particularly in neurons in the brain and spinal cord. Progressive damage caused by the buildup of GM2 ganglioside leads to the destruction of these neurons.
Huntington disease is a progressive brain disorder that causes uncontrolled movements, emotional problems, and loss of thinking ability (cognition). Mutations in the HTT gene cause Huntington disease. The HTT gene provides instructions for making a protein called huntingtin. Although the function of this protein is unknown, it appears to play an important role in nerve cells (neurons) in the brain.
The HTT mutation that causes Huntington disease involves a DNA segment known as a CAG trinucleotide repeat. This segment is made up of a series of three DNA building blocks (cytosine, adenine, and guanine) that appear multiple times in a row. Normally, the CAG segment is repeated 10 to 35 times within the gene. In people with Huntington disease, the CAG segment is repeated 36 to more than 120 times. People with 36 to 39 CAG repeats may or may not develop the signs and symptoms of Huntington disease, while people with 40 or more repeats almost always develop the disorder.
An increase in the size of the CAG segment leads to the production of an abnormally long version of the huntingtin protein. The elongated protein is cut into smaller, toxic fragments that bind together and accumulate in neurons, disrupting the normal functions of these cells. The dysfunction and eventual death of neurons in certain areas of the brain underlie the signs and symptoms of Huntington disease.
abnormally long protein and is not functional, repeats CAG
one division; chromosome number stays the same; body cells (somatic cells)
Stages: Prophase (centrioles pull to opposite poles; aster and spindle fibers form; nuclear membrane becomes invisible; chromosomes thicken and become visible); Metaphase (chromosomes move to equator of cell); Anaphase (cytokinesis begins; chromosomes move toward opposite poles of the cell); Telophase (cytokinesis completes; reverse of prophase); Interphase (G1 – much growth and protein synthesis; S – DNA synthesis; G2 – less growth and protein synthesis)
interphase causes an increase in cell number
identical cells to original
ex: if you get a cut you get new skin cells
mitosis: repairing and replacing
Cancer cells keep dividing; do not pause in G2 phase; cells lack contact inhibition
even when theres no room for them
two divisions; chromosome number is halved; sex cells (gametes)
Stages: Prophase I (same as prophase; pairing of homologous chromosomes known as synapsis; exchange of DNA known as crossing over); Metaphase I; Anaphase I; Telophase I (cytokinesis produces 2 haploid cells); Interkinesis (no S phase);
Prophase II; Metaphase II; Anaphase II; and Telophase II (4 haploid cells)
23 cells each
prophase I gives variety
Multiple births; Identical Twins, known as Monozygotic / Maternal - one egg; one sperm; same gender; zygote splits and two individuals develop; one placenta; two umbilical cords; Non-identical Twins, known as Dizygotic / Fraternal - two eggs; two sperm; same or different gender; two zygotes form, and two individuals develop; two placentas; two umbilical cords.
In North America, dizygotic twins occurs about once in 83 conceptions, and triplets about once in 8000 conceptions. A traditional approximation of the incidence of multiple pregnancies is as follows:
Triplets 1:80² = 1:6400
The number of multiple births has increased over the last decades. Much of the increase can probably be attributed to the impact of fertility treatments, such as in-vitro fertilization. Younger patients who undergo treatment with fertility medication containing artificial FSH, followed by intrauterine insemination, are particularly at risk for multiple births of higher order.
Certain factors appear to increase the likelihood that a woman will naturally conceive multiples. These include:
mother's age — women over 35 are more likely to have multiples than younger women.
mother's use of fertility drugs — approximately 35% of pregnancies arising through the use of fertility treatments such as IVF involve more than one child.
1 egg 1 sperm; 2 embryos
dizygotic/fraternal twins are more common
are identical twins whose bodies are joined in utero. A rare phenomenon, the occurrence is estimated to range from 1 in 50,000 births to 1 in 200,000 births, with a somewhat higher incidence in Southwest Asia and Africa. Approximately half are stillborn, and a smaller fraction of pairs born alive have abnormalities incompatible with life. The overall survival rate for conjoined twins is approximately 25%. The condition is more frequently found among females, with a ratio of 3:1.
Two contradicting theories exist to explain the origins of conjoined twins. The older and most generally accepted theory is fission, in which the fertilized egg splits partially. The second theory is fusion, in which a fertilized egg completely separates, but stem cells (which search for similar cells) find like-stem cells on the other twin and fuse the twins together.
The most famous pair of conjoined twins was Chang and Eng Bunker (1811–1874), Thai brothers born in Siam, now Thailand. They traveled with P.T. Barnum's circus for many years and were billed as the Siamese Twins. Chang and Eng were joined by a band of flesh, cartilage, and their fused livers at the torso. In modern times, they could have been easily separated. Due to the brothers' fame and the rarity of the condition, the term came to be used as a synonym for conjoined twins.
Although a change in the DNA sequence occurs, this type of mutation does not change the protein that is to be produced. This is because multiple genetic codons can encode for the same amino acid. Amino acids are coded for by three nucleotide sets called codons. For example, the amino acid arginine is coded for by several DNA codons including CGT, CGC, CGA, and CGG (A = adenine, T = thymine, G = guanine and C = cytosine). If the DNA sequence CGC is changed to CGA, the amino acid arginine will still be produced.
This type of mutation alters the nucleotide sequence so that a different amino acid is produced. This change alters the resulting protein. The change may not have much effect on the protein, may be beneficial to protein function, or may be dangerous. Using our previous example, if the codon for arginine CGC is changed to GGC, the amino acid glycine will be produced instead of arginine.