ULTRASTRUCTURE OF CELLS

OBJECTIVES

• Identify the cell organelles and their respective

functions

• Recognize the differences of bacterial, plant, and

animal cells

• Appreciate importance of cells to an organism

• Prepare fresh mounts of kinds of cells

PLANT CELL

• cell wall

• cell membrane

• nucleus

• cytoplasm

• vacuole

ANIMAL CELL

• cell nucleus

• cytoplasm

BACTERIAL CELL

• movement – jerky

• rod shaped

FUNGAL CELLS

• sporangium

• sporangiophore (hyphae)

• rhizoid

• stolon

COMPARISON

• Size

• Shape

• Protective covering

• Organelles

THE CELL CYCLE

CHROMOSOME NUMBER

• all organisms contain chromosome where genes

are found

• thread-like structures in a cell’s nucleus visible under

microscope only during cell division

• somatic cells (non-reproductive body cell) has a

partner chromosome occurring in pairs

• homologous chromosomes - two members of a pair

chromosome

• diploid – chromosomes occurring in pairs (2n)

• haploid – single set of unpaired chromosome (n)

AUTOSOMES VS SEX CHROMOSOMES

• sex determination is

based on sex

chromosomes

• a pair containing 2 X

chromosomes would

entail female sex and 1 X

and O would entail male

sex

THE CELL CYCLE

• period from beginning of one division to the

beginning of the next division

• generation time – the period between two

successive divisions/complete revolution of the

cycle

• 8 to 20 hours

CELL CYCLE

S Phase

• DNA synthesis

• 10-12 hours

• each replicated DNA

molecules intertwine

held tightly together by

a protein

M Phase

• chromosome

segregation and cell

division

• lesser time

• major events: nuclear

division and

cytoplasmic division

G1 PHASE AND G2 PHASE

• G1 phase is between M-phase and S-phase

• G2 phase is between S-phase and Mitosis

• time delays to allow cell growth

• monitor internal and external environment

• G1 – if external conditions are unfavorable, it

extends to form the G0 phase

CELL CYCLE CONTROL SYSTEM

G1 PHASE AND G2 PHASE

G1 Phase

• event between the

previous cell division

and DNA replication

• cell grows

• longest phase

• synthesis of certain

enzymes used in DNA

replication

G2 Phase

• increased protein

synthesis for

preparation in cell

division

• short phase

• beginning of mitosis

marks the end of G2

INTERPHASE

• period of active growth and maintenance after

mitosis

• synthesizes needed materials

• grows

• chromosomes undergo duplication

LOCATION OF MITOSIS

• meristems (meristo “divided”)

• shoot and root tips (apical meristems)

• thin cylindrical regions that run the entire lengths

of the stems and roots (lateral meristems)

• temporary meristems are produced when a plant

is wounded or encounters a disease

LOCATION OF MITOSIS

MITOSIS

PROPHASE

• chromatin (long, thin, thread (like material of which

chromosomes are composed) condense and coil

into visible chromosome

• chromosomes become shorter and thicker

• centromere – constricted region

• kinetochore – attached to the centromere where

microtubules bind

PROPHASE

• nuclear envelope disappears and breaks apart

• the nucleolus shrinks

• microtubules organize between poles to form the mitotic spindle (aids in movement of chromosome)

METAPHASE

• short period of chromosomes lining up in the

midplane of the cell

• mitotic spindle (visible and made up of

microtubules extending from pole to pole)

ANAPHASE

• once chromatids are no longer attached to their

duplicates they are considered independent

chromosomes

• chromatids move to opposite poles

TELOPHASE

• final stage of mitosis

• chromosomes arrive to the poles and return to their

interphase condition

• new nuclear envelope forms

• nucleoli reorganizes

• spindle fiber disappears

CYTOKINESIS

• division of the

cytoplasm

• begins during telophase

• cell plate → plasma

membrane and cell

walls

MEIOSIS

SEXUAL REPRODUCTION

• reproductive cells (eggs and sperm cells) are called

gametes

• half the diploid number of chromosome

• form a complete new organism by uniting

• ♀ gamete (egg) unites with the ♂ gamete (sperm) =

zygote (fertilized egg)

MEIOSIS

• type of cell division that reduces the number

chromosomes in reproductive cells by half

• “to make smaller”

• haploid cells always contain each homologous pair

• when two numbers of haploid cells unite during

fertilization, the normal diploid number of the cell is

restored

PROPHASE I

• elongated and thin homologous chromosomes lie

side by side (synapsis)

• crossing over – pieces of maternal and paternal chromatids

break off and rejoined to the opposite chromatid; produces

new combination of genes

• genetic recombination – enhances variety among

sexually produced offspring

PROPHASE I

METAPHASE I

• homologous chromosomes line up in pairs along the

midplane

ANAPHASE I

• homologous chromosome

separate with one moving

toward one pole and the

other toward the other pole

• chromosomes remain united

at centromere

TELOPHASE I

• duplicated chromosome

(one of each homologous

pair) at each pole

MEIOSIS II

PLANT LIFE CYCLE

• diploid plant (sporophyte) produces haploid spores

by meiosis

• Spores divide by mitosis to give rise to a multicellular

plant known as gametophyte whose cells all

contain haploid number of the chromosomes

SPERMATOGENESIS & OOGENESIS

• spermatogenesis

• produces mature sperm cells

• all four products can acquire a flagellum for locomotion

and a cap-like structure that aid in the penetration of the

cell

• oogenesis

• production of mature ovum or egg cell

• only one of four meiotic products develops into functional gamete

BRING THE FOLLOWING

• Onion root tips

• prepare by placing in a vial containing 70% ETHYL alcohol

• glass slide, cover slips

• gillette blade or scalpel

• check flies next meeting