Bio 105: Cell Division - Napa Valley College · Cell Cycle: Stages of Cell Division •2 main phases –Interphase •Prepares for cell division • •DNA replication –Mitotic

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Bio 105: Cell Division

Laboratory 8

Cell Division

• Starts with DNA Replication

DNA Replication

• When does DNA replicate? – Just prior to cell division

• Multicellular Organisms –Grow

–Replace old cells

• Unicellular Organisms –Reproduce

DNA Replication

• Chromosomes

–DNA wound up in coils and folded

• Replicated DNA

– “Duplicated state”

• 2 strands

• Chromatids or sister chromatids

• Held together by a centromere

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DNA Replication

• After replication

– Each chromosome will be made of 2 sister chromatids

–Remember – chromosomes come in pairs

2 chromosomes, each with 2 chromatids

Remember DNA is in the nucleus

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Cell Cycle: Stages of Cell Division

• 2 main phases

– Interphase

• Prepares for cell division

• DNA replication

–Mitotic phase

• Chromosomes separate

• Cell Divides

Cell Cycle: Stages of Cell Division

• Average animal cell cycle

– about 24 hours

• Mitosis

–About 30 minutes

• Most of the time spend in G1

–Cells grows in size

–About 12 hours

Interphase

• Cell grows

• Makes new cellular components

• DNA is replicated **

• Check points

End of Interphase: DNA has replicated

Mitosis

• 4 Phases

–Prophase

–Metaphase

–Anaphase

– Telophase Think about how hard it would be to divide the DNA into two equal parts if it was in the uncondensed form

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Mitosis: Prophase

• Chromosomes condense

• Nuclear membrane breaks down

• Two centrioles (one centrosome) begin to move to opposite ends of the cell

• Microtubules form

Microtubules Mitosis: Prophase

Mitosis: Metaphase

• Microtubules (mitotic spindles) attach to the chromosomes

• Microtubules line up the chromosomes at the center of the cell (the equator)

Mitosis: Metaphase

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Mitosis: Anaphase

• Sister chromatids are pulled apart by the microtubules

• Chromatids move towards the poles. Chromatids Chromosomes

Mitosis: Anaphase

Mitosis: Telophase

• Chromosomes begin to uncondense

• Nuclear membrane forms

• Cell begins to divide in half

Mitosis: Telophase

Cytokinesis

• Cell divides completely forming two separate cells

Cytokinesis

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Cell Division - Mitosis

• Mitosis Overview

–https://www.youtube.com/watch?v=C6hn3sA0ip0

Review Questions

• Where does DNA replication take place?

• When does DNA replication take place?

• During what stage does the nuclear membrane breakdown?

• During what stage do the chromosomes line up at the equator?

• During what stage do the chromosomes being to uncondense?

Review Questions

• At the end of mitosis, how many cells are there?

• At the end of mitosis, how many chromosomes are there in each cell?

• At the end of mitosis, are the chromosomes in the duplicated state?

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Cell Types

• Mitosis

–Occurs in all the body’s cells except for gametes

– Somatic cells

• Gametes

–Cells responsible for reproduction

Cell Division

• Gametes

– Sperm

– Eggs

• Cell division = Meiosis

–Halving their number of chromosomes

Terminology

• Diploid – Cells that have 46 chromosomes or 23 pairs

– All somatic cells are diploid (2n)

• Haploid – Cells that have 23 chromosomes

– All gametes are haploid (1n)

• Meiosis – Diploid cell divides to produce haploid

reproductive cells

Meiosis

• Interphase

–Chromosomes (DNA) duplicated

• Then there are 2 cell divisions

• Pairs of chromosomes

• Each chromosome has 2 chromatids after DNA replication

Meiosis

• Interphase

–Chromosomes duplicate

• 1st division

–Chromosome pairs separate and cell divides

• 2nd division

–Chromatids separate and cell divides

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Meiosis • DNA replicates

–Chromosomes become duplicated

–Cell is diploid (2n)

• Homologous chromosomes separate and cell divides

• The chromatids separate and cell divides

–4 haploid cells (1n)

Meiosis

• Forms gametes

• Start as diploid cells and end up haploid cells

• 2 stages –Meiosis I

–Meiosis II

– Each stage has Prophase, Metaphase, Anaphase and Telophase

Meiosis – Crossing Over

• End of Interphase – DNA is replicated

• Prophase I

–Duplicated chromosomes condense and intertwine

–Produces genetic variation = crossing over

–Genetic material is exchanged between the homologous chromosomes

Meiosis: Prophase I

• Duplicated chromosomes condense and crossover

• Nuclear membrane breaks down

• 2 Centrioles (centrosomes) begin to move to opposite ends of cell

• Microtubules form

Meiosis: Metaphase I • Microtubules (mitotic

spindles) attach to the chromosomes

• Microtubules line up the chromosomes at the center of the cell (the equator)

• Chromosomes arrange themselves randomly – Independent

assortment

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Meiosis: Anaphase I

• Chromosomes in the pairs are separated

• Different than mitosis

–Here the chromosomes in a pair are separated from each other

–Now 23 chromosomes are on each side

Meiosis: Telophase I

• Nuclear membrane forms

• Cell divides in half

• Have 2 haploid cells (1n)

• 23 chromosomes total

• Chromosomes are in duplicated form

• Cell now enters Meiosis II

Meiosis II

Meiosis II • Prophase II

– 23 chromosomes are already condensed – Nuclear membrane dissolves

• Metaphase II – Chromosomes line up at the equator

• Anaphase II – Chromatids separate

• Telophase II – Cells separate

• Result: 4 haploid cells, each has 23 chromosomes NOT in the duplicated state

Meiosis

• https://www.youtube.com/watch?v=-DLGfd-Wpr4

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Review Questions • At the end of Meiosis I, how many cells

are there?

• At the end of Meiosis I, are these haploid or diploid cells?

• At the end of Meiosis I, how many chromosomes are there in each cell?

• At the end of Meiosis I, are the chromosomes in the duplicated state?

Review Questions

• At the end of Meiosis II, how many cells are there?

• At the end of Meiosis II, are these cells haploid or diploid?

• At the end of Meiosis II, how many chromosomes are there in each cell?

• At the end of Meiosis II, are the chromosomes in the duplicated state?

Genetic Diversity

• 2 places in meiosis that contribute to genetic diversity

–Prophase I – Crossing over

–Metaphase I – Independent Assortment

Meiosis and Gender

• Gametes

–Contain 23 chromosomes

–Not in duplicated form

• One of these chromosomes will be a sex chromosome

• Eggs = X chromosome

• Sperm = either X or Y chromosome

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Spermatogenesis

• Sperm produced in male testes

• One cell 4 sperm

• Each sperm:

–23 chromosomes, not in duplicated form

–X or Y chromosome

– Small head and long tail

– Flagellum for locomotion

Spermatogenesis

• Contain the genetic material to deliver to the egg

• Head contain the chromosomes and lots of mitochondria

• About 400 million sperm are produced each day

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Oogenesis – Egg Formation • Ovaries produce eggs

• One cell one egg and 3 non-functioning “polar bodies”

– One egg gets most of the cytoplasm

– Other 3 not able to survive

– 23 chromosomes, not in duplicated form

– X chromosome

– One egg is large enough to support the embryo

Oogenesis

• All of the cells that produce the eggs are made before the female mother is even born

• Each month one of these cells will leave the ovary and go on to mature

–Produce the egg and polar bodies

Review

• Mitosis and Meiosis both start with a diploid cell (46 chromosomes, 23 pairs)

• Before both the DNA replicates forming duplicated chromosomes, each containing two chromatids

• Mitosis – somatic cells –Cells other than gametes

• Meiosis – produces gametes

Review

• Mitosis

– The chromatids are separated to produce 2 cells

• Each with 46 chromosomes

• 23 pairs of non-duplicated chromosomes

• Cells are diploid (2n)

• No exchanging of genetic material

Review

• Meiosis I – Pairs of chromosomes line up and the

chromosomes are separated – Results in 2 cells, each with 23 chromosomes

in the duplicated state

• Meiosis II – Chromatids separated – Results in 2 haploid cells that contain 23 non-

duplicated chromosomes

• One original cell 4 haploid cells

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Important Concepts

• Know the 2 phases of the cell cycle – Interphase and Mitosis

– Know what happens in each phase

• Mitosis – Know each stage, the order of the stages and what

happens in each stage

• Be able to recognize each stage of mitosis from pictures, models and microscope slides

• Why are check points important in interphase?

Important Concepts

• Know what state the cell and the chromosomes are in at the beginning and end of – Mitosis – Meiosis I – Meiosis II – Example: Are the cells haploid or diploid? Are

the chromosomes duplicated or not? How many chromosomes are there in the cell? Are they in pairs?

Important Concepts

• Know which cells undergo mitosis vs meiosis

• How is genetic diversity introduced into meiosis

–What are the events that add to diversity?

–When does each event occur?

Important Concepts

• How is the gender of the offspring determined?

• How many functioning sperm are produced from one spermatocyte?

• What sex chromosomes can a sperm have?

• How many functioning eggs are produced from one oocyte?

• What sex chromosomes do eggs have?

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Definitions

• Gametes

• Somatic cells

• Diploid

• Haploid

• Crossing over

• Independent assortment

• Cytokinesis

• Centromere

• Centrioles

• Centrosome

• Chromatid

• Polar bodies

• Spermatogenesis

• Oogenesis

The End