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49 Cards in this Set
- Front
- Back
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Normally__ strands of DNA (chromosomes) in human cells
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46
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Specific regions of DNA are
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genes
Genes contain hereditary info that distinguishes us from each other Genes also contain coded information required for synthesis of proteins and enzymes needed for normal function of cell |
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Replication
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Prior to cell division, DNA material in original cell must be duplicated so that after division, each new cell contains full amount of DNA material
Original polynucleotide strand of DNA serves as template to guide synthesis of new complementary polynucleotide of DNA |
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Genes
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Located in nuclei of all cells (approximately 100,000 in each cell)
Control heredity Control day-to-day function of all cells Determine which structures, enzymes, and chemicals are synthesized within cell Each gene is a segment of DNA that codes for a protein, which in turn codes for a trait (skin tone, eye color..etc) DNA controls formation of ribonucleic acid (RNA) RNA spreads through cell to control formation of specific protein Proteins may be structural Combine with lipids and carbohydrates to form structures of organelles Most proteins are enzymes Catalyze chemical reactions within cell Genes attached end to end in long double-stranded helical DNA molecules found in nucleus |
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Building Blocks of DNA
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Phosphoric acid
Deoxyribose (sugar) These form helical strands (backbone of DNA) Four nitrogen bases: 2 purines Adenine Guanine 2 pyrimidines Thymine Cytosine |
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DNA formed when >>>>
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deoxyribose combines with phosphoric acid and then attaches to one of the four bases
Four separate nucleotides formed Purine and pyrimidine bases always bind in particular order by loose H+ bonds Adenine always binds with thymine Guanine always binds with cytosine |
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Organization of DNA
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H+ bonds loose allowing strands to pull apart easily
When strands split, purine and pyrimidine bases form genetic code that determine sequence of amino acids in protein that’s to be synthesized Genetic code listed as “triplets” of bases In following example GGC, AGA, CTT is genetic code for DNA strand |
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RNA
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So far, all reactions have taken place in nucleus of cell
Need RNA to carry information into cytoplasm Synthesis of RNA occurs in nucleus |
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Types of RNA
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Messenger RNA
Carries genetic code to cytoplasm Transfer RNA Transports activated amino acids to ribosomes Ribosomal RNA Forms ribosomes which are structures on which protein molecules are assembled |
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Messenger RNA
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During synthesis of RNA, strands of DNA temporarily separate
One strand is used as template for synthesis of RNA Code triplets in DNA cause formation of complimentary code triplets (codons) in RNA Other strand of DNA remains inactive until after RNA formed and then rejoins with same DNA strand |
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RNA is similar to DNA except:
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Has one strand instead of two
Has ribose instead of deoxyribose Has uracil instead of thymine G-C C-G A-U U-A |
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RNA nucleotides (cytosine, guanine, uracil, adenine) activated by _____ ________
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RNA polymerase
Causes phosphate radicals to be added to nucleotides building RNA molecule Also causes temporary unwinding and separation of DNA helix |
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Transcription
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In DNA strand just before initial gene is promotor (TATA sequence)
RNA polymerase attaches to promoter Attachment causes unwinding and separation of DNA helix Moves along DNA strand unwinding and separating it Adds new activated RNA nucleotide to end of new chain by: H+ bond forms between RNA and DNA bases When RNA polymerase reaches chain-terminating sequence, process stops DNA helix rejoins forcing RNA chain away |
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DNA code transmitted in complementary form to RNA chain
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Messenger RNA
Carries genetic code to cytoplasm RNA nucleotides in unpaired single strands Contain codons which form 20 common amino acids in protein molecules One codon (AUG) signals start manufacturing protein 3 codons (UAA, UAG, UGA) signal stop manufacturing protein See table 3-1 page 32 in Guyton |
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Transfer RNA
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Transfers amino acid molecules to protein molecules as protein synthesized
Each type binds specifically with 1 of 20 amino acids Acts as carrier to transport specific amino acid to ribosomes where protein molecules are forming |
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Ribosomal RNA
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Makes up about 60% of ribosome
Ribosome – manufacturing plant for protein molecules Ribosomal RNA works with transfer RNA (transports amino acids to ribosome) and messenger RNA (provides info needed for proper sequencing of amino acids for specific protein) |
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Translation
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Formation of proteins on ribosomes
Messenger RNA comes in contact with ribosome Travels thru ribosome beginning at predetermined end of RNA molecule (chain-initiating codon) Protein molecule is formed by translation as mRNA moves thru ribosome Codons are read and transfer delivers appropriate anti-codon to bond and form protein molecule |
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When does transcription begin?
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Transcription begins when the enzyme RNA polymerase II binds to the promoter region of DNA
Initiates process of making a molecule of messenger mRNA Sequence of bases in DNA—the order of A, T, C, and G—dictates sequence of mRNA which will be formed mRNA moves into cytoplasm and temporarily attaches to ribosomes In ribosome, mRNA directs assembly of amino acids (20 kinds) into proteins Each amino acid is specified by a code of three bases |
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Transfer RNA (tRNA) helps
...how? |
Each tRNA molecule contains its own triplet code (to match the mRNA code) and ferries a particular kind of amino acid to the ribosomes
Amino acids are linked through chemical bonds to create a protein molecule Proteins typically consist of hundreds of amino acids The sequence of bases in DNA determines the sequence of mRNA, which then determines the linear sequence of amino acids in a protein |
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Enzyme Regulation of Intracellular Function
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May be activated or inhibited
Inhibition Substances in cell may have direct feedback on enzyme causing inhibition Negative feedback control Responsible for controlling intracellular concentrations of some substances |
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Activation
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Usually occurs in response to intracellular needs
Example – depletion of ATP Breakdown product cAMP forms Causes activation of phosphorylase that splits glycogen into glucose |
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Life Cycle of Cell
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Genes also determine when or whether cells divide to form new cells
Life cycle of cell From reproduction until next reproduction Usually 10-30 hours Reproduction begins in nucleus First step – replication of all DNA in chromosomes |
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Reproduction Begins with DNA Replication
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Both strands of DNA are replicated from end to end instead of small areas (like RNA transcription)
DNA polymerase causes replication much like RNA polymerase Each exactly duplicated DNA helix remains attached to original DNA Two DNA helixes are coiled together Enzymes cause splitting Produces two identical strands of DNA |
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DNA Replication
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During hour before mitosis, active repair and proofreading of DNA strands occurs
Special enzymes cut out defective areas and rematch nucleotides with appropriate complementary nucleotide Mistakes are rare but known as mutation |
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Chromosomes
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DNA helixes in nucleus packaged in chromosomes
46 chromosomes arranged in 23 pairs in human cells One chromosome in each pair comes from mother and one from father In 22 of 23 pairs, members of each pair identical to each other In 23rd pair (sex chromosomes) 2 “X” chromosomes in females 1 “X” and 1 “Y” in males |
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Centromere
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Point at which paired chromosomes meet or are held together
Point of division Location of centromere helps identify chromosome |
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Common Pathology
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Chromosome abnormalities leading known cause of retardation and miscarriage
Trisomy Cell that has 3 copies of one chromosome Monosomy Cell that has 1 copy of given chromosome Monosomy of any chromosome except sex chromosomes is lethal |
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Trisomy
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Can occur for any chromosome
Most frequent in live births are trisomy 13,18, 21 Trisomy 21 (Down’s Syndrome) First described in 1866 Seen in 1 in 800 births Risk increases with maternal age Younger than 30 – risk 1 in 1000 Increases after 35 years to 3-5% in women > 45 Usually symptoms like Alzheimer’s by age 40 ¾ of fetuses with known Down’s spontaneously aborted or still births 20% die within first 10 years If live longer than 10 years, life expectancy now up to about 60 years |
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Characteristics of children with trisomy 21
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Mental retardation with IQ 25 – 50
Distinctive facial appearance Protruding tongue Poor muscle tone Short stature Congenital heart defects in 1/3 to 1/2 Frequent respiratory infections Susceptible to leukemia |
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Anesthesia Implications Trisomy 21
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Congenital cardiac lesions – prophylactic antibiotics
Endocardial cushion defects (40%) VSD (27%) PDA (12%) Tetralogy of Fallot (8%) Frequent upper respiratory infections Hypothyroidism |
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Anesthesia Implications Trisomy 21 ...airway
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Hypotonia
Less muscle relaxation Potential airway problems Instability of atlanto-occipital joint (15%) Usually asymptomatic Treat like unstable Increased incidence of subglottic stenosis Large tongue Small mouth Hypoplastic mandible Difficult intubation, CHD, use less muscle relaxant |
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Sex Chromosome Abnormalities
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1 in 1000 newborn females have 3 X chromosomes in each cell – Trisomy X
No overt physical abnormalities Sterile, menstrual irregularity and retardation may be seen Klinefelter syndrome At least 2 X chromosomes and one Y Male appearance Sterile Female-like breasts Single X chromosome and no Y leads to Turner syndrome Short stature Female genitalia Webbed neck Underdeveloped breasts Imperfectly developed ovaries |
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Cell Reproduction
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Most cells don’t last for lifetime of individual
New cells are created as fast as old ones die Process of reproduction of sperm and egg cells (gametes) called meiosis Process of division or reproduction of other cells (somatic cells) called mitosis Mass of cell and all its contents must be duplicated before division Most of this work occurs in interphase part of cell cycle (life cycle 10-30 hours) During interphase, DNA and RNA synthesis occurs Actual stage of mitosis lasts for only about 30 minutes |
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Chromosome Replication
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Once DNA has been replicated, chromosome replication occurs
2 newly formed chromosomes remain attached to each other at centromere near center Duplicated but still attached chromosomes called chromatids |
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Cell Mitosis – Process of Cell Division
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After each chromosome has been replicated to form two chromatids, cell mitosis follows automatically within 1-2 hours
Phases of mitosis Prophase Metaphase Anaphase Telophase |
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Prophase
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Spindle fibers form in cytoplasm and radiate from centrioles located near opposite poles of nucleus
Roll of spindle fiber is to pull chromosomes to opposite sides of cell Each chromosome seen as two identical halves called chromatids Nuclear membrane disappears |
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Metaphase
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Spindle fibers begin to pull centromeres of chromosomes aligning them in middle of spindle
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Anaphase
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Centromeres split
Spindle fibers shorten pulling chromatids, centromere first toward opposite sides of cell When chromatids are separated, they’re considered to be chromosomes Cell has 92 chromosomes during this stage – 46 at each side of cell |
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Telophase
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New nuclear membrane forms around each group of 46 chromosomes
Spindle fibers disappear Cytoplasm divides into roughly equal parts Two identical cells have been formed from original cell |
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Mitosis
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Prophase
Spindle fibers from centrioles Centrioles migrate to opposite sides Nuclear membrane disappears Metaphase Spindle fibers align centromeres in center of cell Anaphase Centromeres split pull chromatids to opposite sides forming 92 chromosomes Telophase Nuclear membrane forms Spindle fibers disappear Cytoplasm divides Two new cells |
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Control of Reproduction
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Many cells reproduce constantly
Bone marrow Skin Some take years to reproduce Smooth muscle cells Some don’t reproduce for entire lifetime Neurons Skeletal muscle cells Liver tissue Insufficiency of cells causes rapid reproduction 7/8 of liver can be removed and cells of remaining 1/8 grow and divide to return liver mass to near normal Same occurs for most cells except the highly differentiated nerve and muscle cells |
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Cell Differentiation
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Changes in cell properties as they grow and divide in the embryo
Differentiation results selective repression of genes not loss of genes Example Replacement of nucleus of frog ovum with nucleus from intestinal mucosal cell results in formation of normal frog |
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Cancer...causes...
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Caused by mutation or abnormal activation of genes that control growth and mitosis
Abnormal genes called oncogenes Cells also have antioncogenes that suppress activation of oncogenes Loss or inactivation of antioncogenes lead to cancer |
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Only fraction of mutated cells lead to cancer because
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Mutated cells have lower survival rates
Mutated cells have normal negative feedback control that prevents excessive growth Often destroyed by immune system Several differentiated oncogenes needed to cause cancer Rapid reproduction may occur but another mutant gene needed to form blood vessels supply cell |
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T or F: Precision of replication of DNA and proofreading process help prevent mutation
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True
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Probability of mutation increased by
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Ionizing radiation (x-rays, UV-light) – rupture DNA strands
Physical irritants – continued abrasion of intestinal tract by some food types Hereditary tendency – mutated gene inherited Viruses – leukemia results from virus |
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Chemical substances (carcinogens)
that cause greatest number of deaths |
cigarette smoke
Increases incidence of lung, bladder, pancreas, kidney, larynx, oral, and esophagus cancer 20 carcinogens in cigarette smoke causing lung cancer alone have been identified |
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Differences between cancer cells and normal cells
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Grow faster – don’t require same growth factors normal cells need
Less adhesive to each other – spread through tissues – metastasis Some produce angiogenic factors – grow own blood vessels |
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How does cancer kill?
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Kills because cancer cells compete with normal cells for nutrients
Continue to proliferate indefinitely Deprive normal cells of essential nutrients Normal tissues die from starvation |
