Part of Exercise 4 of Human Anatomy & Physiology Laboratory Manual, 8th Edition, by Elaine Marieb

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Dr.Susan Maskel BIO 105 Western Connecticut State University A&P I

BIO 211 Naugatuck Valley Community College A&P I

Some graphics and all definitions courtesy of Benjamin Cummings

www.lawrencegaltman.com

Background

Information

CHROMOSOMES

DNA (deoxyribonucleic

acid) stores genetic information

Protein

controls processes

DNA2 strands double helixeach strand contains:

sugars (deoxyribose)

phosphates (PO4)nitrogenous bases

adeninethymineguaninecytosine

Structure of Components of DNA

-O - P = O

O-

O

phosphate

DNA

S

S

S

S

P

P

P

B

B

B

B

B

B

B

B

S

S

S

S

P

P

P

PPS B B S

Key:

S = sugar

P = phosphate

B = base

sugar-phosphate backbone

nitrogenous bases form “rungs of ladder”

Bases in DNA

•Adenine (A)•Thymine (T)•Cytosine (C)•Guanine (G)

•Specificity of base pairing A - T C - G

DNA

Types of Chromosomes

duplicated (2 ds DNAs +

protein)

unduplicated (1 double stranded (ds) DNA + protein)

Duplicated Chromosomes

DNA

sister chromatids

centromere

Humans have 46 chromosomes in their somatic (i.e., not sperm or

egg) cells.

Diploid number = 2 N = 46

Humans have 23 chromosomes in their sex cells (sperm & egg).

Haploid number = 1 N = 23

THE CELL CYCLE

not dividing

dividing

At any given time, a cell is either:

When Cells are Not Dividing:• Interphase

– G1•Normal cell metabolism•Synthesis of proteins not used for mitosis•Chromosomes unduplicated•Centrioles replicate

– S•Normal cell metabolism•DNA synthesis (DNA replication):

unduplicated chromosomes duplicated chromosomes

– G2•Normal cell metabolism•Synthesis of proteins used for mitosis•Chromosomes duplicated

• DNA unzips• New nucleotides

(sugar-phosphate-base combinations) add according to specificity of base pairing

DNA Replication

old strand

new strand

forming sister chromatid of duplicated

chromosome

NOTE:

The 2 forming sister

chromatids have an

identical base

sequence to each

other.

Semiconservative Replication: each

sister chromatid has 1 new & 1 old

strand

ds DNA of unduplicate

d chromosom

e

sister chromatids

of duplicated

chromosome

When Cells Are Dividing:• Nuclear Division

–Mitosis•occurs in somatic cells•maintains the # of chromosomes

–Meiosis•occurs in sex cells•halves the # of chromosomes

• Cytokinesis–division of cytoplasm–occurs during mitosis & meiosis

G1 unduplicated chromosomes

S chromosomes

duplicate

G2 duplicated

chromosomesM

start with duplicated

chromosomes; end with

unduplicated chromosomes

Before mitosis begins,

the cell is in INTERPHASE.

INTERPHASE

•cell is not dividing•includes G1, S & G2•nuclear membrane

visible•nucleoli visible•chromatin in nucleus•NOT PART OF MITOSIS

Interphase

-nuclear membrane intactnucleolus visiblechromatin not visible

NOTE:

Interphase

Nuclear membrane present Chromatin not

visible

Interphase

Nuclear division in

somatic cells takes place via

MITOSIS.

prophase

metaphase

anaphase

telophase

PROPHASE (1 - several hours)

• nuclear membrane disappears• nucleoli disappear• chromatin chromosomes• centrioles move to opposite

poles of cell• spindle & asters form

Centrioles

made of microtubule

s

at end of G1,

centrioles replicated (to form 2

pairs)

Spindle & Asters

aster

probably anchors apparatus to cell

membrane

spindle

helps organize

chromosomes during mitosis

Prophase

In this hypothetical cell, 2 N = 4. In humans, 2 N = 46.

nuclear membrane disappears nucleolus disappearschromatin chromosomesspindle & asters form

NOTE:

Prophase

Nuclear membrane still present but is

disappearing

chromosomes

Prophase

METAPHASE (5 - 15 minutes)

•chromosomes line up on center of spindle

•chromosomes are attached to spindle fibers in area of centromere

Metaphase

In this hypothetical cell, 2 N = 4. In humans, 2 N = 46.

chromosomes lined up in single file in center of

spindle

NOTE:

Metaphase

Chromosomes lined up on center of

spindle

aster

aster

Metaphase

ANAPHASE (2 - 10 minutes)

•spindle fibers pulled toward opposite poles of cell

•centromeres splits•sister chromatids pulled

toward opposite poles of cell as microtubules of spindle shorten

Anaphase

In this hypothetical cell, 2 N = 4. In humans, 2 N = 46.

NOTE:

sister chromatids being pulled toward opposite

poles of cell

Anaphase

chromatids separated & being pulled toward opposite poles of cell

aster

aster

Anaphase

TELOPHASE (10 - 30 minutes)

• cleavage furrow formed• cell invaginates at cleavage

furrow until 2 daughter cells formed (= cytokinesis)

• opposite of prophase– nuclear membrane reappears– nucleoli reappear– chromosomes uncoil to

chromatin– spindle & asters disappear

Telophase

In this hypothetical cell, 2 N = 4. In humans, 2 N = 46.

NOTE:

cleavage furrow forms;2 daughter cells will form; the opposite of prophase will occur

Telophase

unduplicated chromosomes unwinding

unduplicated chromosomes unwinding

cleavage furrow

Telophase

spindle

INTERPHASE PROPHASE METAPHASE

ANAPHASE TELOPHASE TELOPHASE

Part of Exercise 4 of Human Anatomy & Physiology Laboratory Manual, 8th Edition, by Elaine Marieb

Dr.Susan Maskel BIO 105 Western Connecticut State University A&P I

BIO 211 Naugatuck Valley Community College A&P I

Some graphics and all definitions courtesy of Benjamin Cummings

www.lawrencegaltman.com

Name the phase of mitosis

indicated.

Answer: metaphase

Name the phase of mitosis

indicated.

AnswerAnaphas

e

Name the phase of mitosis seen.

ANSWER: prophase

Name the phases of mitosis indicated.

1

2

3

4

ANSWERS

1

2

3

4

1 = metaphase

2 = telophase

3 = anaphase

4 = prophase

Name the phases of mitosis indicated.

12

3

ANSWERS

12

3

1 = anaphase

2 = metaphase

3 = anaphase

Now it’s YOUR turn to identify stages of mitosis

with a microscope!