Understanding Growth & Development 1. FORMATION OF GAMETES Meiosis 2.
At sexual maturity, the ovaries and testes produce haploid gametes Gametes are the only types of...
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Transcript of At sexual maturity, the ovaries and testes produce haploid gametes Gametes are the only types of...
• At sexual maturity, the ovaries and testes produce haploid gametes
• Gametes are the only types of human cells produced by meiosis, rather than mitosis
• Meiosis results in one set of chromosomes in each gamete
• Fertilization and meiosis alternate in sexual life cycles to maintain chromosome number
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 13-5Key
Haploid (n)Diploid (2n)
Haploid gametes (n = 23)
Egg (n)
Sperm (n)
MEIOSIS FERTILIZATION
Ovary Testis
Diploidzygote(2n = 46)
Mitosis anddevelopment
Multicellular diploidadults (2n = 46)
Crossing Over
• Crossing over produces recombinant chromosomes, which combine genes inherited from each parent
• Crossing over begins very early in prophase I, as homologous chromosomes pair up gene by gene
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 13-12-5Prophase Iof meiosis
Pair ofhomologs
Nonsisterchromatidsheld togetherduring synapsis
Chiasma
Centromere
Anaphase I
Anaphase II
Daughtercells
Recombinant chromosomes
TEM
The Law of Segregation
• When Mendel crossed contrasting, true-breeding white and purple flowered pea plants, all of the F1 hybrids were purple
• When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers, but some had white
• Mendel discovered a ratio of about three to one, purple to white flowers, in the F2 generation
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 14-3-3
EXPERIMENT
P Generation
(true-breeding parents) Purple
flowers Whiteflowers
F1 Generation
(hybrids) All plants hadpurple flowers
F2 Generation
705 purple-floweredplants
224 white-floweredplants
The Behavior of Recessive Alleles
• Recessively inherited disorders show up only in individuals homozygous for the allele
• Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal (i.e., pigmented)
• Albinism is a recessive condition characterized by a lack of pigmentation in skin and hair
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 14-16
Parents
Normal Normal
Sperm
Eggs
Normal Normal(carrier)
Normal(carrier) Albino
Aa Aa
A
AAA
Aa
a
Aaaa
a
Inheritance of Sex-Linked Genes
• The sex chromosomes have genes for many characters unrelated to sex
• A gene located on either sex chromosome is called a sex-linked gene
• In humans, sex-linked usually refers to a gene on the larger X chromosome
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 15-7
(a) (b) (c)
XNXN XnY XNXn XNY XNXn XnY
YXnSpermYXNSpermYXnSperm
XNXnEggs XN
XN XNXn
XNY
XNY
Eggs XN
Xn
XNXN
XnXN
XNY
XnY
Eggs XN
Xn
XNXn
XnXn
XNY
XnY
• Genes that are far apart on the same chromosome can have a recombination frequency near 50%
• Such genes are physically linked, but genetically unlinked, and behave as if found on different chromosomes
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 15-12Mutant phenotypes
Shortaristae
Blackbody
Cinnabareyes
Vestigialwings
Browneyes
Redeyes
Normalwings
Redeyes
Graybody
Long aristae(appendageson head)
Wild-type phenotypes
0 48.5 57.5 67.0 104.5
Alterations of Chromosome Structure
• Breakage of a chromosome can lead to four types of changes in chromosome structure:– Deletion removes a chromosomal segment– Duplication repeats a segment– Inversion reverses a segment within a chromosome– Translocation moves a segment from one
chromosome to another
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 15-15
DeletionA B C D E F G H A B C E F G H(a)
(b)
(c)
(d)
Duplication
Inversion
Reciprocaltranslocation
A B C D E F G H
A B C D E F G H
A B C D E F G H
A B C B C D E F G H
A D C B E F G H
M N O C D E F G H
M N O P Q R A B P Q R
The Basic Principle: Base Pairing to a Template Strand
• Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication
• In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Animation: DNA Replication OverviewAnimation: DNA Replication Overview
Fig. 16-11EXPERIMENT
RESULTS
CONCLUSION
1 2
43
Conservative model
Semiconservative model
Dispersive model
Bacteria cultured in medium containing 15N
Bacteria transferred to medium containing 14NDNA
sample centrifuged after 20 min (after first application)
DNA sample centrifuged after 40 min (after second replication)
More dense
Less dense
Second replication
First replication
Antiparallel Elongation
• The antiparallel structure of the double helix (two strands oriented in opposite directions) affects replication
• DNA polymerases add nucleotides only to the free 3end of a growing strand; therefore, a new DNA strand can elongate only in the 5to3direction
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 16-17
OverviewOrigin of replicationLeading strand
Leading strand
Lagging strand
Lagging strandOverall
directions of
replicationLeading strand
Lagging strand
Helicase
Parental DNA
DNA pol III
PrimerPrimase
DNA ligase
DNA pol IIIDNA pol I
Single-strand
binding protein
53
5
55
5
3
3
33
13 2
4
• Eukaryotic chromosomal DNA molecules have at their ends nucleotide sequences called telomeres
• Telomeres do not prevent the shortening of DNA molecules, but they do postpone the erosion of genes near the ends of DNA molecules
• It has been proposed that the shortening of telomeres is connected to aging
• If chromosomes of germ cells became shorter in every cell cycle, essential genes would eventually be missing from the gametes they produce
• An enzyme called telomerase catalyzes the lengthening of telomeres in germ cells
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 16-20
1 µm
Evolution of Cell Signaling
• A signal transduction pathway is a series of steps by which a signal on a cell’s surface is converted into a specific cellular response
• Signal transduction pathways convert signals on a cell’s surface into cellular responses
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 11-2
Receptor factor
a factor
a
a
Exchangeof matingfactors
Yeast cell,mating type a
Yeast cell,mating type
Mating
New a/cell
a/
1
2
3
Local and Long-Distance Signaling
• Cells in a multicellular organism communicate by chemical messengers
• Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells
• In local signaling, animal cells may communicate by direct contact, or cell-cell recognition
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 11-4Plasma membranes
Gap junctionsbetween animal cells
(a) Cell junctions
Plasmodesmatabetween plant cells
(b) Cell-cell recognition
• During transcription, one of the two DNA strands called the template strand provides a template for ordering the sequence of nucleotides in an RNA transcript
• During translation, the mRNA base triplets, called codons, are read in the 5 to 3 direction
• Each codon specifies the amino acid to be placed at the corresponding position along a polypeptide
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 17-4
DNAmolecule
Gene 1
Gene 2
Gene 3
DNAtemplatestrand
TRANSCRIPTION
TRANSLATION
mRNA
Protein
Codon
Amino acid
Split Genes and RNA Splicing
• Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that lie between coding regions
• These noncoding regions are called intervening sequences, or introns
• The other regions are called exons because they are eventually expressed, usually translated into amino acid sequences
• RNA splicing removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 17-10
Pre-mRNA
mRNA
Codingsegment
Introns cut out andexons spliced together
5 Cap
Exon Intron5
1 30 31 104
Exon Intron
105
Exon
146
3Poly-A tail
Poly-A tail5 Cap
5 UTR 3 UTR1 146
Histone Modifications
• In histone acetylation, acetyl groups are attached to positively charged lysines in histone tails
• This process loosens chromatin structure, thereby promoting the initiation of transcription
• The addition of methyl groups (methylation) can condense chromatin; the addition of phosphate groups (phosphorylation) next to a methylated amino acid can loosen chromatin
Animation: DNA PackingAnimation: DNA Packing
Fig. 18-7
Histonetails
DNAdouble helix
(a) Histone tails protrude outward from a nucleosome
Acetylated histones
Aminoacidsavailablefor chemicalmodification
(b) Acetylation of histone tails promotes loose chromatin structure that permits transcription
Unacetylated histones
Protein Processing and Degradation
• After translation, various types of protein processing, including cleavage and the addition of chemical groups, are subject to control
• Proteasomes are giant protein complexes that bind protein molecules and degrade them
Animation: Protein DegradationAnimation: Protein Degradation
Animation: Protein ProcessingAnimation: Protein Processing
Fig. 18-12
Proteasomeand ubiquitinto be recycledProteasome
Proteinfragments(peptides)Protein entering a
proteasome
Ubiquitinatedprotein
Protein tobe degraded
Ubiquitin
Epigenetic Inheritance
• Although the chromatin modifications just discussed do not alter DNA sequence, they may be passed to future generations of cells
• The inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence is called epigenetic inheritance
The Lytic Cycle
• The lytic cycle is a phage reproductive cycle that culminates in the death of the host cell
• The lytic cycle produces new phages and digests the host’s cell wall, releasing the progeny viruses
• A phage that reproduces only by the lytic cycle is called a virulent phage
• Bacteria have defenses against phages, including restriction enzymes that recognize and cut up certain phage DNA
Animation: Phage T4 Lytic CycleAnimation: Phage T4 Lytic Cycle
Fig. 19-5-5
Phage assembly
Head Tail Tail fibers
Assembly
Release
Synthesis of viralgenomes andproteins
Entry of phageDNA anddegradation ofhost DNA
Attachment1
2
4
5
3
The Lysogenic Cycle
• The lysogenic cycle replicates the phage genome without destroying the host
• The viral DNA molecule is incorporated into the host cell’s chromosome
• This integrated viral DNA is known as a prophage• Every time the host divides, it copies the phage
DNA and passes the copies to daughter cells
Animation: Phage Lambda Lysogenic and Lytic CyclesAnimation: Phage Lambda Lysogenic and Lytic Cycles
Fig. 19-6
PhageDNA
Phage
The phage injects its DNA.
Bacterialchromosome
Phage DNAcircularizes.
Daughter cellwith prophage
Occasionally, a prophageexits the bacterialchromosome,initiating a lytic cycle.
Cell divisionsproducepopulation ofbacteria infectedwith the prophage.
The cell lyses, releasing phages.
Lytic cycle
Lytic cycleis induced or Lysogenic cycle
is entered
Lysogenic cycle
Prophage
The bacterium reproduces,copying the prophage andtransmitting it to daughter cells.
Phage DNA integrates intothe bacterial chromosome,becoming a prophage.
New phage DNA and proteinsare synthesized andassembled into phages.
DNA Cloning and Its Applications• Most methods for cloning pieces of DNA in the
laboratory share general features, such as the use of bacteria and their plasmids
• Plasmids are small circular DNA molecules that replicate separately from the bacterial chromosome
• Cloned genes are useful for making copies of a particular gene and producing a protein product
Fig. 20-2a
DNA of chromosome
Cell containing geneof interest
Gene inserted intoplasmid
Plasmid put intobacterial cell
RecombinantDNA (plasmid)
Recombinantbacterium
Bacterialchromosome
Bacterium
Gene ofinterest
Plasmid
2
1
2
Using Restriction Enzymes to Make Recombinant DNA
• Bacterial restriction enzymes cut DNA molecules at specific DNA sequences called restriction sites
• A restriction enzyme usually makes many cuts, yielding restriction fragments
• The most useful restriction enzymes cut DNA in a staggered way, producing fragments with “sticky ends” that bond with complementary sticky ends of other fragments
Animation: Restriction EnzymesAnimation: Restriction Enzymes
Fig. 20-4-4
Bacterial cell
Bacterial plasmid
lacZ gene
Hummingbird cell
Gene of interest
Hummingbird DNA fragments
Restrictionsite
Stickyends
ampR gene
TECHNIQUE
Recombinant plasmids
Nonrecombinant plasmid
Bacteria carryingplasmids
RESULTS
Colony carrying non-recombinant plasmidwith intact lacZ gene
One of manybacterialclones
Colony carrying recombinant plasmid with disrupted lacZ gene
Amplifying DNA in Vitro: The Polymerase Chain Reaction (PCR)
• The polymerase chain reaction, PCR, can produce many copies of a specific target segment of DNA
• A three-step cycle—heating, cooling, and replication—brings about a chain reaction that produces an exponentially growing population of identical DNA molecules
Fig. 20-8a
5
Genomic DNA
TECHNIQUETargetsequence
3
3 5
• Host cells in culture can be engineered to secrete a protein as it is made
• This is useful for the production of insulin, human growth hormones, and vaccines
Protein Production in Cell Cultures
• Transgenic animals are made by introducing genes from one species into the genome of another animal
• Transgenic animals are pharmaceutical “factories,” producers of large amounts of otherwise rare substances for medical use
• “Pharm” plants are also being developed to make human proteins for medical use
Protein Production by “Pharm” Animals and Plants
Movement of Transposons and Retrotransposons
• Eukaryotic transposable elements are of two types:– Transposons, which move within a genome by
means of a DNA intermediate– Retrotransposons, which move by means of an RNA
intermediate
Fig. 21-9
TransposonNew copy of transposon
Insertion
Transposonis copied
Mobile transposon
DNA ofgenome
(a) Transposon movement (“copy-and-paste” mechanism)
RetrotransposonNew copy of
retrotransposon
Insertion
Reversetranscriptase
RNA
(b) Retrotransposon movement
Widespread Conservation of Developmental Genes Among Animals
• Molecular analysis of the homeotic genes in Drosophila has shown that they all include a sequence called a homeobox
• An identical or very similar nucleotide sequence has been discovered in the homeotic genes of both vertebrates and invertebrates
• Homeobox genes code for a domain that allows a protein to bind to DNA and to function as a transcription regulator
• Homeotic genes in animals are called *Hox genes*
Fig. 21-17
Adultfruit fly
Fruit fly embryo(10 hours)
Flychromosome
Mousechromosomes
Mouse embryo(12 days)
Adult mouse
• Unit 3C13 21 & 22, 75&81C14 12&15, 77&78C15 27&29, 52&54, 64&65, C16 33&41, 56&71 77/79&78C17 23&25, 49&50, C18 29&30, 33 (example epigentetics) 54&55C19 21&26, 27&29 C20 6&9, 11&22 42&44, 96&97C21 41& 42, 82&83