Nov 06, 2021
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A, Double helix. Shown with the phosphodiester backbone as a ribbon on top and a space-filling model on the bottom. The bases protrude into the interior of the helix where they hold it together by base pairing. The backbone forms two grooves, the larger major groove and the smaller minor groove. B, Base pairing holds strands together. The hydrogen (H)-bonds that form between A and T and between G and C are shown with dashed lines. These produce AT and GC base pairs that hold the two strands together. This always pairs a purine with a pyrimidine, keeping the diameter of the double helix constant. A, Adenine; C, cytosine; G, guanine; T, thymine. (From Raven PH et al: Biology, ed 8, New York, 2008, McGraw-Hill.)
3DNA
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.V1 (2:12)
V2 ( 5: 23)
4DNA (contd)
Chromosomes contain genes.
Genes are the basic unit of inheritance and are composed of DNA.
DNA subunit or nucleotide contains:
One pentose sugar (deoxyribose)
One phosphate group
One nitrogenous base
Cytosine (C), thymine (T), adenine (A), guanine (G)
DNA has a double helix structure.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.DNA as the Genetic Code
DNA provides the code for all body proteins.
Proteins are composed of one or more polypeptides.
Polypeptides are composed of amino acids; there are twenty (20) amino acids:
The sequence of three bases (codons) direct the production of amino acids.
Termination and nonsense codons stop the production of protein.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.6Replication
The DNA strand is untwisted and unzipped.
Single strand acts as a template.
DNA polymerase pairs the complementary bases.
Adenine-thymine; cytosine-guanine
DNA polymerase adds new nucleotides and proofs the new protein; if not correct, the incorrect nucleotide is excised and replaced.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.-The DNA bases code for amino acids which in turn make up proteins. The amino acids are specified by triplet codons od nitrogenous bases
-Transcription and translation are 2 processes in which proteins are specified by DNA and involves RNA. RNA is chemically similar to DNA except it is single stranded and has Uracil instead of Thymine as one of its 4 bases.
-Meiosis is process by which haploid cells are made from diploid cells
7Replication (contd)
Replication process
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Replication (contd) Question 1
Which information is correct regarding DNA polymerase?
DNA polymerase functions to:
Signal the end of a gene.
Pull apart a portion of a DNA strand.
Add the correct nucleotides to a DNA strand.
Provide a template for the sequence of mRNA nucleotides.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Elsevier items and derived items 2009, 2005, 2001 by Saunders, an imprint of Elsevier Inc.
9Mutation
Is any inherited alteration of genetic material.
Chromosome aberrations in number or structure
Base pair substitution or missense mutation
One base pair is substituted for another; may result in changes in amino acid sequence.
May or may not cause disease or problems.
Frameshift mutation
Involves the insertion or deletion of one or more base pairs to the DNA molecule.
Mutagens: Are agents, such as radiation and chemicals, that increase the frequency of mutations.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.10From Genes to Proteins
DNA is formed in the nucleus; protein is formed in the cytoplasm.
Transcription and translation: DNA code is transported from the nucleus to the cytoplasm, and protein is subsequently formed.
Ribonucleic acid (RNA) mediates both processes.
RNA is a single strand.
Uracil rather than thymine is one of the four bases; all the rest are the same as DNA.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Transcription
RNA is synthesized from the DNA template via RNA polymerase.
RNA polymerase binds to the promoter site on DNA.
DNA specifies a sequence of mRNA.
Transcription continues until the termination sequence is reached.
mRNA then moves out of the nucleus and into the cytoplasm.
Gene splicing occurs.
Introns and extrons
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Transcription (contd)
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.General Scheme of RNA Transcription. In transcription of messenger RNA (mRNA), a DNA molecule unzips in the region of the gene to be transcribed. RNA nucleotides already present in the nucleus temporarily attach themselves to exposed DNA bases along one strand of the unzipped DNA molecule according to the principle of complementary pairing. As the RNA nucleotides attach to the exposed DNA, they bind to each other and form a chainlike RNA strand called a messenger RNA (mRNA) molecule. Notice that the new mRNA strand is an exact copy of the base sequence on the opposite side of the DNA molecule. As in all metabolic processes, the formation of mRNA is controlled by an enzyme in this case, the enzyme is called RNA polymerase. (From Ignatavicius DD, Workman LD: Medical-surgical nursing, ed 6, St Louis, 2010, Saunders.)
13Translation
Is the process by which RNA directs the synthesis of a polypeptide via the interaction with transfer RNA (tRNA).
tRNA contains a sequence of nucleotides (anticodon) complementary to the triad of nucleotides on the mRNA strand (codon).
Ribosome is the site of protein synthesis.
Ribosome helps mRNA and tRNA make polypeptides.
When ribosome arrives at a termination signal on the mRNA sequence, translation and polypeptide formation cease.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Ribosomes are key
14Translation (contd) Question 2
At what site does protein synthesis occur?
The site of protein synthesis is the:
Codon
Intron
Ribosome
Anticodon
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Elsevier items and derived items 2009, 2005, 2001 by Saunders, an imprint of Elsevier Inc.
15Chromosomes
Somatic cells
Contain 46 chromosomes (23 pairs)
One member from the mother; one from the father
Diploid cells
Gametes
Sperm and egg cells
Contain 23 chromosomes
Haploid cells
One member of each chromosome pair
Meiosis
Formation of haploid cells from diploid cells
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.-Human cells consist of diploid somatic cells (body cells) and haploid gametes (sperm and egg cells)
16Chromosomes (contd)
Autosomes
Are the first 22 of the 23 pairs of chromosomes in males and females.
The two members are virtually identical and are thus said to be homologous.
Sex chromosomes
Make up the remaining pair of chromosomes.
In females, it is a homologous pair (XX).
In males, it is a nonhomologous pair (XY).
Karyotype
The length and centromere location determine the ordered display of chromosomes.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.-Humans have 23 pairs of chromosomes ; 22 of the 23 pairs are autosomes ( are homologous/the same) in both males and females. The remaining pair consists of sex chromosomes.
-Females have 2 homologous X chromosomes as the sex chromosomes. Males have an X and Y nonhomogolous chromosome.
17Chromosomal Aberrations
Euploid cells
Have a multiple of the normal number of chromosomes.
Haploid and diploid cells are euploid forms.
Polyploid cells: An euploid cell has more than the diploid number.
Triploidy: Is a zygote that has three copies of each chromosome.
Tetraploidy: Has four copies of each chromosome (92 total).
Triploid and tetraploid fetuses do not survive or are stillborn or spontaneously aborted.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.18Chromosomal Aberrations (contd)
Aneuploidy
Is a somatic cell that does not contain a multiple of 23 chromosomes.
Trisomy (trisomic): Is a cell that contains three copies of one chromosome.
Infants can survive with trisomy of certain chromosomes.
Monosomy
Is the presence of only one copy of any chromosome.
Is often fatal.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.-Aneuploid cells contain 3 copies of one chromosome is known as trisomy
-Monosomy is the presence of only one copy of a chromosome in a diploid cell
-Abnormalities of chromosomal structure include deletions, duplications, inversions, and translocations.
19Chromosomal Aberrations (contd)
Aneuploidy of sex chromosomes
Usually presents less serious consequences than autosomes.
Y chromosome usually causes no problems since it contains little genetic material.
For the X chromosome, inactivation of extra chromosomes largely diminishes their effect.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Chromosomal Aberrations (contd)
Nondisjunction
Is usually the cause of aneuploidy.
Is the failure of homologous chromosomes or sister chromatids to separate normally during meiosis or mitosis.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.-Difficulty in separation of chromosomes
21Chromosomal Aberrations (contd)
Nondisjunction (contd)
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Nondisjunction Causes Aneuploidy When Chromosomes or Sister Chromatids Fail to Divide Properly. (From Jorde LB et al: Medical genetics, ed 5, Philadelphia, 2016, Elsevier.)
22Autosomal Aneuploidy
Trisomy
Chromosomes 13, 18, and 21 can survive; most others do not.
Partial trisomy
Only an extra portion of a chromosome is present in each cell.
Is not as severe as trisomies.
Chromosomal mosaics
Are trisomies that occur in only some cells of the body.
Body has two or more different cell lines, each of which has a different karyotype.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Autosomal Aneuploidy (contd)
Down syndrom
Is the best-known example of aneuploidy.
Trisomy 21
Occurs 1 in 800 live births.
Manifestations: Mental challenges; low nasal bridge; epicanthal folds; protruding tongue; flat, low-set ears; and poor muscle tone.
Risk increases with maternal age.
Has an increased risk of congenital heart disease, respiratory infections, and leukemia.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Autosomal Aneuploidy (contd)
Down syndrome (contd)
Copyright 014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Down Syndrome. A, The karyotype of Down syndrome consists of 47 chromosomes and shows trisomy 21. B, A child with Down syndrome. (From Damjanov I: Pathology for the health professions, ed 4, Philadelphia, 2012, Saunders.)
25Sex Chromosome Aneuploidy
Occurs 1 in 400 males and 1 in 650 females.
Trisomy X is one of the most common aneuploidy.
Females have three X chromosomes.
Occurs 1 in 1000 female births.
Symptoms are variable and include sterility, menstrual irregularity, and/or cognitive deficits.
Symptoms worsen with each additional X chromosome.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.-Mental function is more severely impaired with greater number of trisomy in X chromosomes, for example some patients have 4-5 X chromosomes instead of just 3.
26Sex Chromosome Aneuploidy (contd)
Turner syndrome
Females have only one X chromosome
Denoted as karyotype 45,X.
Characteristics include:
Absence of ovaries (sterile)
Short stature
Webbing of the neck
Widely spaced nipples
High number of aborted fetuses
X chromosome that is usually inherited from the mother
Occurs 1 in 2500 female births.
Teenagers receive estrogen.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.-Most teenagers treated with estrogen to promote development of secondary sexual characteristics. Dose is then reduced to maintain characteristics and help avoid osteoporosis. Human growth hormone sometimes given to increase stature.
27Sex Chromosome Aneuploidy (contd)
Turner syndrome (contd)
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Turner Syndrome. A sex chromosome is missing, and the persons chromosomes are 45,X. Characteristic signs are short stature, female genitalia abnormality, webbed neck, shieldlike chest with underdeveloped breasts and widely spaced nipples, and imperfectly developed ovaries. (From Patton KT, Thibodeau GA: Anatomy & physiology, ed 8, St Louis, 2013, Mosby.)
28Sex Chromosome Aneuploidy (contd)
Klinefelter syndrome
Individuals with at least one Y and two X chromosomes.
Characteristics include:
Male appearance
Femalelike breasts (gynecomastia)
Small testes
Sparse body hair
1 in 1000 male births
Some individuals can be XXXY and XXXXY; will have male appearance; abnormalities will increase with each X; can also have an extra Y chromosome.
Disorder increases with the mothers age.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.-Stature is often elevated along with moderate degree of mental impairment.
29Sex Chromosome Aneuploidy (contd)
Klinefelter syndrome (contd)
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Klinefelter Syndrome. This young man exhibits many characteristics of Klinefelter syndrome: small testes, some development of the breasts, sparse body hair, and long limbs. This syndrome results from the presence of two or more X chromosomes with one Y chromosome (genotypes XXY or XXXY, for example). (Courtesy Nancy S. Wexler, PhD, Columbia University. Picked up from Patton KT, Thibodeau GA: Anatomy & physiology, ed 9, St Louis, 2016, Mosby.)
30Sex Chromosome Aneuploidy (contd) Question 3
A female has one X chromosome. Which diagnosis will the nurse observe documented on the chart?
Trisomy X syndrome
Klinefelter syndrome
Fragile X syndrome
Turner syndrome
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Elsevier items and derived items 2009, 2005, 2001 by Saunders, an imprint of Elsevier Inc.
31Abnormalities of Chromosomal Structure
Effects may or may not have serious consequences.
Chromosome breakage
If a chromosome break occurs, then the break is usually repaired with no damage.
Breaks can stay or can heal in a way that alters the structure of the chromosome.
Can occur spontaneously.
Agents of chromosome breakage include Ionizing radiation, chemicals, and viruses.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Abnormalities of Chromosomal Structure (contd)
Deletions
Chromosome breakage or loss of DNA
Example: Cri du chat syndrome or cry of the cat
Low birth weight, mentally challenged, and microcephaly
Duplications
Excess genetic material
Usually have less serious consequences
Inversion
Chromosomal rearrangement in which a chromosome segment is inverted: ABCDEFG becomes ABEDCFG
Usually affects offspring
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.33
33Abnormalities of Chromosomal Structure (contd)
Infant with cri du chat (5p deletion) syndrome
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.-Occurs as a result of deletion of part of short arm portion of chromosome 5. Although one copy of chromosome is normal, serious consequences can still occur with deletions.
-Name derived from distinctive cry of newborn with this condition,
-Other symptoms include severe mental retardation, microcephaly, heart defects, and typical facial appearance seen in figure above.
34Abnormalities of Chromosomal Structure (contd
Fragile X syndrome
Site is on the long arm of the X chromosome; has an elevated number of repeated DNA sequences.
Is associated with being mentally challenged; is second in occurrence to Down syndrome.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.-Caused by an elevated number of repeated DNA sequences (more than 200) in the first exon of the fragile X gene. DNA replication becomes unstable, more than 20 genetic diseases are linked to this mechanism.
35Elements of Formal Genetics
Genetic inheritance
Mechanisms by which an individuals set of paired chromosomes produces traits.
Explains the patterns of inheritance for traits and diseases that appear in families.
Mendelian traits
Are inherited traits primarily attributed to single genes.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.Elements of Formal Genetics (contd)
Locus: Is the location occupied by a gene on a chromosome.
Allele: Is one of several different forms of a gene at a locus.
One member of a gene from the mother; one member of a gene from the father
Homozygous: When genes are identical
Heterozygous: When genes are different
Polymorphism or polymorphic
Is a locus that has two or more alleles that occur with appreciable frequency.
th a carrier for an autosomal dominant gene.
