Chapter 6Chapter 6

Cell ReproductionCell Reproduction

ChromosomesChromosomes

• The growth and The growth and development of development of your body are your body are controlled by controlled by instructions instructions contained in your contained in your DNADNA

DNA “decides” what you DNA “decides” what you will be…..will be…..

DNA & ChromosomesDNA & Chromosomes

• Very long Very long moleculesmolecules

• Wound around Wound around protein moleculesprotein molecules

• Compacts during Compacts during cell replication to cell replication to form form chromosomeschromosomes

If you unraveled all your chromosomes from all of your cells and laid out the DNA end to end, the strands would stretch from the Earth to the Moon about 6,000 times.

EukaryoticEukaryoticChromosomesChromosomes

• Made of Made of chromatinchromatin– Complex of DNA & Complex of DNA &

proteinprotein

• DNA coils tightly DNA coils tightly and forms and forms chromosomes chromosomes when a cell is when a cell is preparing to preparing to divide.divide.

DNA -- Overview

Karyotype – a picture of Karyotype – a picture of your chromosomesyour chromosomes

• Chromosomes Chromosomes are isolated are isolated and stainedand stained

• You have 46 You have 46 chromosomeschromosomes

• 23 pairs23 pairs

Another type of karyotypeAnother type of karyotype

Diploid …2n=46Diploid …2n=46

• When human cells have 23 pairs of When human cells have 23 pairs of chromosomes they are “diploid”chromosomes they are “diploid”

• Nearly all cells are diploidNearly all cells are diploid

Haploid…1n=23Haploid…1n=23

• Haploid cells Haploid cells only have 1 only have 1 copy of each copy of each chromosomechromosome

• Sperm and Sperm and ova are ova are haploidhaploid

Sex ChromosomesSex Chromosomes

• 1 pair of your 23 1 pair of your 23 chromosomes chromosomes determines your determines your sexsex

• These are known These are known as the sex as the sex chromosomes X chromosomes X and Yand Y

Females have 2 Females have 2 X ChromosomesX Chromosomes

Males have 1 X and 1 Y Males have 1 X and 1 Y chromosomechromosome

Chapter 6.2Chapter 6.2

•Mitosis and Mitosis and Cell Cell DivisionDivision

Cell Growth and Cell Growth and ReplicationReplication

• Cells grow to Cells grow to their maximum, their maximum, efficient size.efficient size.

• Remember..the Remember..the surface to surface to volume ratio is volume ratio is critical.critical.

When a cell reaches When a cell reaches maximum size….maximum size….

• It may stop growing It may stop growing • It may divideIt may divide

•Both processes are Both processes are controlled by the cell’s DNAcontrolled by the cell’s DNA

Prokaryotic Cell Prokaryotic Cell ReproductionReproduction

• Bacteria have only 1 circular chromosomeBacteria have only 1 circular chromosome

• Bacterial cell reproduction is more “simple” Bacterial cell reproduction is more “simple” than eukaryotic cell divisionthan eukaryotic cell division

Eukaryotic Cell DivisionEukaryotic Cell Division

• Eukaryotes contain more DNA the Eukaryotes contain more DNA the prokaryotesprokaryotes

• Eukaryotic cell reproduction is Eukaryotic cell reproduction is more complicated than prokaryotic more complicated than prokaryotic cell reproductioncell reproduction

• Mitosis and cell divisionMitosis and cell division

MitosisMitosis

• Process by which the nucleus Process by which the nucleus of a eukaryotic cell divides to of a eukaryotic cell divides to form two nucleiform two nuclei

• Each nucleus contains a Each nucleus contains a complete set of chromosomescomplete set of chromosomes

4 Phases of Mitosis4 Phases of Mitosis

• ProphaseProphase• MetaphaseMetaphase• AnaphaseAnaphase• TelophaseTelophase

But 1But 1stst…the DNA has to …the DNA has to replicatereplicate

• InterphaseInterphase

Interphase Interphase (DNA Replication)(DNA Replication)

• Cell carries on Cell carries on normal normal functionsfunctions

• ***DNA ***DNA replicates****replicates****

• Chromosomes Chromosomes are not visibleare not visible

InterphaseInterphase(DNA Replication)(DNA Replication)

** No chromosomes are visible**

Prophase - Prophase - Mitosis beginsMitosis begins

• DNA coils into DNA coils into chromosomeschromosomes

• Nuclear envelope Nuclear envelope breaks upbreaks up

• Spindle fibers, Spindle fibers, network of protein network of protein cables, forms.cables, forms.

ProphaseProphase

Early Prophase

Late Prophase

MetaphaseMetaphase

• Chromosomes Chromosomes attach to the attach to the spindle fibersspindle fibers

• Line up across Line up across center of cellcenter of cell

MetaphaseMetaphase

AnaphaseAnaphase

• Chromosomes Chromosomes separate from one separate from one anotheranother

• ““Reeled” to Reeled” to opposite sides of opposite sides of the cellthe cell

• Spindle fibers Spindle fibers begin to break begin to break down.down.

AnaphaseAnaphase

Telophase &Telophase &CytokinesisCytokinesis

• Chromosomes reach Chromosomes reach opposite ends of the opposite ends of the cellcell

• Nuclear membrane Nuclear membrane reformsreforms

• Chromosomes uncoilChromosomes uncoil• Spindle fibers Spindle fibers

disappeardisappear• Cell divides into 2 = Cell divides into 2 =

cytokinesiscytokinesis

Telophase & CytokinesisTelophase & Cytokinesis

Early Telophase

Late Telophase

Plant MitosisPlant Mitosis

Instead of pinching into 2, a cell wall is formed between the new

cells.

Onion Root TipsOnion Root Tips

Brain Aerobics…..Brain Aerobics…..

• Every second ~25 million cells are Every second ~25 million cells are produced by mitosis in the human produced by mitosis in the human body.body.

• How many cells are produced by How many cells are produced by mitosis in a day?mitosis in a day?

Brain Aerobics Answer…..Brain Aerobics Answer…..

25 million/second x 60 sec x 60 minutes x 24 hours =

2.16 trillion cells/day !

The Cell CycleThe Cell Cycle

• Most of a cell’s life Most of a cell’s life time is spent growing time is spent growing NOT dividing.NOT dividing.

• A cell cycles between A cell cycles between periods of growth and periods of growth and division.division.

The Cell CycleThe Cell Cycle

• 5 phase sequence of growth and 5 phase sequence of growth and division in eukaryotic cellsdivision in eukaryotic cells

Interphase is the most active part Interphase is the most active part of the cell cycleof the cell cycle

• Taking in foodTaking in food• Converting energyConverting energy• Discarding wastesDiscarding wastes• GrowingGrowing• DifferentiatingDifferentiating• **Duplicating genetic **Duplicating genetic

material and material and organelles**organelles**

Interphase can be divided into 3 Interphase can be divided into 3 stages of the cell cyclestages of the cell cycle

•GG11 Phase Phase

•S PhaseS Phase

•GG22 Phase Phase

GG11 Phase Phase

• Also known as 1Also known as 1stst Gap Gap

• Time of intense growthTime of intense growth

• Some cells spend most of their Some cells spend most of their lives in Glives in G11

S PhaseS Phase

• S stands for “synthesis”S stands for “synthesis”

• DNA is copiedDNA is copied

GG22 Phase Phase

• Also known as 2Also known as 2ndnd Gap Gap• Final stage of interphaseFinal stage of interphase• Cell continues to growCell continues to grow• Duplicates organellesDuplicates organelles• Prepares for cell divisionPrepares for cell division

Cell CycleCell Cycle

Controlling the Cell CycleControlling the Cell Cycle

• Cell cycles are controlled by special Cell cycles are controlled by special proteins called cyclins.proteins called cyclins.

• S-cyclin stimulates DNA replication S-cyclin stimulates DNA replication in S phasein S phase

• M-cyclin triggers mitosisM-cyclin triggers mitosis

Cyclins are influenced by Cyclins are influenced by growth factorsgrowth factors

• Can turn on a gene Can turn on a gene that makes a that makes a particular cyclin.particular cyclin.

• Can block the action Can block the action of a cyclin.of a cyclin.

• Help to control cell Help to control cell cyclescycles

Factor

Growth

What happens when the What happens when the cell cycle malfunctions?cell cycle malfunctions?

It can be disastrous – It can be disastrous – even life threatening!even life threatening!

When cells don’t stop When cells don’t stop dividing…dividing…

• Cells begin to divide Cells begin to divide uncontrollablyuncontrollably

• Produces a “clump” of cellsProduces a “clump” of cells

•TumorTumor

Benign TumorsBenign Tumors

•Excess cell growth Excess cell growth remains localizedremains localized

•Usually harmlessUsually harmless

Benign Eyelid TumorBenign Eyelid TumorBefore & after SurgeryBefore & after Surgery

Malignant TumorsMalignant Tumors

•Excess cell growth Excess cell growth invades other tissuesinvades other tissues

•Can be extremely Can be extremely seriousserious

•CancerCancer

CancerCancer

A disease characterized A disease characterized by invasive, by invasive,

uncontrolled cell uncontrolled cell division and growthdivision and growth

Breast CancerBreast Cancer

• Every 12 minutes a Every 12 minutes a woman in America woman in America dies of breast dies of breast cancer.cancer.

Breast CancerBreast Cancer

Mammograms & Mammograms & UltrasoundsUltrasounds

• Breast X-rays and images used to Breast X-rays and images used to detect tissue changesdetect tissue changes

• Often find a tumor before it can be Often find a tumor before it can be felt!felt!

Normal & Abnormal Normal & Abnormal MammogramsMammograms

Breast Breast Cancer Cancer CellCell

Usually round – very mobile

Can grow in liquids

Abnormal proteins and lipids on cell membrane

Doesn’t react to chemical signals in a usual manner

How does a cell become How does a cell become cancerous?cancerous?

• Loses regulated cell divisionLoses regulated cell division• Penetrates or maneuvers around Penetrates or maneuvers around

protective membrane barriersprotective membrane barriers• Invades other tissuesInvades other tissues• Maintains nutrient and oxygen Maintains nutrient and oxygen

supplysupply

Why does a cell become Why does a cell become cancerous?cancerous?

•Cancer cells have defective Cancer cells have defective cell cycle control genescell cycle control genes

•These genes have changes These genes have changes or mutations.or mutations.

Is cancer hereditary?Is cancer hereditary?

• Not usually.Not usually.• Cancer mutations generally occur in Cancer mutations generally occur in

body tissues such as skin or lungs.body tissues such as skin or lungs.

• BUT..if mutations occur in eggs or BUT..if mutations occur in eggs or sperm, then there is a n increased sperm, then there is a n increased likelihood of developing cancer later in likelihood of developing cancer later in life.life.

What factors contribute to What factors contribute to cancer development?cancer development?

• RadiationRadiation– UV lightUV light

• Cigarette smokeCigarette smoke

• Diet & obesity may also be factorsDiet & obesity may also be factors

RadiationRadiationUV lightUV light

Cigarette smokeCigarette smoke

Half of all teenagers who are currently smoking will die from diseases caused by tobacco if they continue to smoke.

It’s your choice!It’s your choice!

Diet & ObesityDiet & Obesity

Chapter 7Chapter 7 •How Gametes FormHow Gametes Form

Nearly all of your cells are Nearly all of your cells are diploid…diploid…

•2n2n•46 chromosomes46 chromosomes•23 pairs23 pairs

•Except……Except……

GametesGametes

• Reproductive cellsReproductive cells• 1n1n• HaploidHaploid• 23 single 23 single

chromosomeschromosomes

MeiosisMeiosis

• A 2 staged form of A 2 staged form of cell division in cell division in which the which the chromosome chromosome number is halvednumber is halved

46 chromosomes

23

chromosomes

Meiosis begins by replicating the Meiosis begins by replicating the chromosomeschromosomes

• This step is identical to mitosis.This step is identical to mitosis.

The homologous The homologous chromosomes then pair.chromosomes then pair.

• The centromeres and chromosomes do The centromeres and chromosomes do not split apart during the first stage of not split apart during the first stage of

meiosis – Meiosis Imeiosis – Meiosis I

The first division reduces the The first division reduces the number of chromosomes by 1/2number of chromosomes by 1/2

The second division, Meiosis II, The second division, Meiosis II, splits the chromosomessplits the chromosomes

• The centromeres and sister The centromeres and sister chromatids divide.chromatids divide.

The End The End result…result…

Crossing-OverCrossing-OverA source of Genetic VariationA source of Genetic Variation

• Chromosomes line Chromosomes line up during first up during first division of Meiosisdivision of Meiosis

• Homologous Homologous chromosomes can chromosomes can cross overcross over

The new The new chromosomes are chromosomes are no longer exactly no longer exactly like the parent like the parent chromosomes..chromosomes..they are a they are a combination .combination .

Advantages…Advantages…

• Great genetic Great genetic diversitydiversity

• Genetic variationGenetic variation• Enables natural Enables natural

selection to occurselection to occur