Cells-Concept 1-3.pptx

Cells-Concept 1

Cell Theory

Scientists Contributing to Cell Theory

slice of cork.

– _{First to identify cells and name them}

• _{Leeuwenhoek- used more powerful microscope.}

– _{First to describe live cells}

• _{Schleiden- first to say plants are made of cells}

• _{Schwann-first to say all living things (added animals)}

are made of cells

• _{Virchow- proposed all cells come from other living}

cells

Cell Theory 3 Principles

1. All organisms are made up of cells

2. All existing cells are produced by other living cells

There are two main types of cells:

Prokaryotic

• _{Single celled} • _{Lack a nucleus}

• _{No membrane bound} organelles

• _{Divide by binary} fission

Eukaryotic

• _{Single or multi-celled} • _{Nucleus surrounded by}

a membrane containing DNA

• _{Membrane bound} organelles

Prokaryotic

Eukaryotic

Nucleus? No Yes- it is surrounded by a membrane and contains DNA

Membrane-bound organelles?

No Yes

Division? Binary fission mitosis

Size? 0.1-10 _μm 10-100 μm

Cell walls? Bacteria, fungi, and

All cells share some characteristics:

• _{Genetic Material- DNA/RNA} • Enclosed by a membrane

• Filled with cytoplasm

Cells-Concept 2

Homeostasis

= The need of an organism to maintain and

regulate constant or stable internal

conditions

– _{Temp., pH, and the concentration of other} materials and nutrients must be maintained within a relatively narrow margin

• _{Much of homeostasis is maintained by the cell}

Cell

Membrane

• _{The cell membrane is said to be selectively}

permeable, meaning certain substances can move across it freely, while others must move through the “gate”.

Passive Transport

• _{Passive transport-movement of molecules}

across a cell membrane without energy from the cell because they move down the

concentration gradient

– _{Examples: Simple diffusion ,osmosis and facilitated}

diffusion

Simple Diffusion

•

The spreading out of molecules

across a membrane until they are

equally concentrated on both sides

of the membrane.

–

Down the concentration gradient

Facilitated Diffusion

•

A

transport protein

acts as a protein channel

to help (facilitate) the diffusion of molecules

that normally couldn’t pass through the cell

membrane

–_{This is still passive because no energy is} required.

Ex. Glucose

Osmosis

•

Osmosis

is the diffusion of

water

across

the cell membrane.

•

As in diffusion, molecules move from an

Osmosis Cont…

•

Solutions can be isotonic, hypertonic, or

hypotonic.

– _{Hypertonic- has a higher concentration in}

the solution than in the cell. What will happen?

– _{Hypotonic- has a lower concentration in the}

solution than in the cell. What will happen?

– _{Isotonic- the cell and the solution have the}

Active Transport

•

Active transport

uses energy (in the form

of ATP) from the cell to move molecules

up or against

the concentration gradient,

from low to high concentration.

– _{Examples: molecular pumps, endocytosis} and exocytosis

Molecular Pumps

•

Energy used to pump molecules

across the membrane, against the

concentration gradient

–

Cell is maintaining homeostasis

Ex. Sodium-potassium pump is used to pump ions in and out of the cell to cause muscle

Endocytosis

•

In endocytosis, cells

import

large

amounts of materials into the cell.

–

Ex. Your immune system does this!

White blood cells engulf bacteria to

fight infection

Exocytosis

•

Exocytosis allows a cell to

export

large

amounts of materials out of the cell.

–

Ex. Nerve cells release neurotransmitters

to pass a signal to the brain.

Cells-Concept 3

Levels of Organization

• _{Organism – one individual, living creature capable of life}

(one member of a species)

• _{Organ System – a distinct set of organs within an organism}

that work together as a unit for a common function (ex. digestive system)

• _{Organ – comprised of several types of tissue that work}

together for a certain purpose (ex. stomach)

• _{Tissue – a group of identical cells working together for a}

common function (ex. muscle cells used for contraction)

• _{Cell – simplest form of life capable of existing independently;}

Each human starts as a fertilized egg..

•

Cell division

can give rise to many

identical

cells

•

As division proceeds, cells go through

differentiation

: a process that creates

special

structures and functions

What will division create?

• _{Division creates two cells with identical DNA} • _{When cells differentiate, they turn on and off}

parts of the DNA

• _{Differentiation is irreversible…} • _{Skin cells create skin cells}

• _{Muscle creates muscle cells} and so on…

• _{Only stem cells can become one} or more types of specialized

Stem Cells

• _{Definition: unspecialized cells that continually} reproduce and can, under the right conditions, differentiate into various cell types

• _{Embryonic Stem Cells: cells}

that have never differentiated (pluripotent)

• _{Adult Stem Cells: cells found}

in adult bone marrow that can become bone, blood,

The Cell Cycle

• _{Cell Cycle: A repeated}

pattern of growth, DNA duplication and cell

division that occurs in

EUKARYOTIC cells

• _{Cell Cycle consists of 3} main phases

– _{Interphse-cell growth} – _Mitosis

The Cell Cycle-Interphase

Interphase: the growth phase of the cell cycle

• _{Interphase is the longest} phase of the cycle

• _{The phase between cell} divisions

• _{By the end of interphase, a} cell has TWO full sets of

Phases of Interphase

•

Interphase has 3 phases:

– _{G1 (gap 1): the cell grows and makes proteins}

– _{S (synthesis): chromosomes replicate and divide} to form identical sister chromatids held together by centromere

Mitosis requires chromosomes

• _{Chromosomes: one long}

continuous thread of DNA that consists of numerous genes

and regulatory information. – _{DNA wraps around proteins}

(histones) that condense it.

– _{Each of your body cells have 46}

chromosomes

– _{In normal body cell,}

Chromosome Structure

•

Centromere: region of the condensed

chromosomes that looks pinched

•

Telomere: ends of the DNA molecule

•

Chromatid

: one half of a

duplicated chromosome

•

Sister chromatids

: two

identical chromatids

held together by

centromere

chromatid

telomere

centromere

Cell Division-Mitosis

•

There are four phases of mitosis

that can be remember by

PMAT

–

P

rophase

Cell Cycle-Mitosis

•

Mitosis

is the actual

division

of the cells

nucleus and it contents.

– _{1 cell becomes 2 cells}

– _{4 strands of DNA (2 sister chromatids) have to break}

Mitosis-Prophase

chromosomes condense and are visible

• _{Nuclear membrane} disappears

• _{Centrioles separate and take}

positions on the opposite sides of cell

• _{Spindle fibers form and}

Mitosis-Metaphase

•

Chromosomes line

up in the middle of

the cell

•

Spindle fibers

connect the

Mitosis- Anaphase

•

Sister chromatids

separate becoming

individual

chromosomes

•

Separated

chromatids move to

opposite poles of

Mitosis-Telophase

•

Chromosomes uncoil

•

Nuclear envelope

forms around

chromosomes at each

side of the cell

•

Spindle fibers break

down and dissolve

Cytokinesis

•

Cytokinesis

differs in animal

and plant cells

–

In animal cells,

the membrane

pinches closed

–

In plant cells, a

Cells Divide at Different Rates

Why Don’t Cell Keep Growing?

How Do Cells Know When To Divide?

key events in the cell cycle

• _{At certain checkpoints the cell responds to various} signals

– _{External signals: like growth factors (chemicals) from}

surrounding cells and physical signals like being too

closely packed or no longer touching another cell where one has died

– _{Internal signals: a cell can receive a signal from its own}

nucleus/DNA that it is time to grow and divide by the

sensing of an external factor that triggers a message sent inside the cell by various enzymes;

•

Some proteins known to be involved are called

cyclins and cyclin-dependent kinases (or CDKs)

Cancer

When the cell cycle fails to function

properly

Cancer Facts:

•

Cancer has begun affecting more people

now that we have infections diseases

under control

•

1 in 3 people will have cancer

– _{1 in 4 males will die from it} – _{1 in 5 females will die from it}

•

The disorder normally manifests itself as

Tumors

• _{Come in two forms:}

– _{Benign: essentially harmless, cells stay in the place}

where the tumor started

– _{Malignant: dangerous, the result of cells that}

metastasize—or move around the body through the lymph or cardiac systems—and start new tumors

elsewhere

How Do Tumors Start?

• _{Often the result of exposure to carcinogens—} cancer causing agents

– _Examples???

– _{They can be physical, biological, or chemical}

• _{Carcinogens mutate DNA}

A Tumor is Simply Unrestrained Cell Growth

•

Cancerous cells tend to:

– _{Create their own growth signals} – _{Reproduce limitlessly}

– _{Evade apoptosis (which is programmed cell} death—a key tool to prevent DNA damage and cancer) Apoptosis video

– _{Sustain angiogenesis (a new discovery…}

cancer cells actually recruit their own blood supply) Angiogenesis video