AP Biology Final

Cells

Cell theory

All organisms are composed of cells

Cells are the smallest living things

Cells arise only from pre-existing cells

Why are cell size limited?

Due to reliance on diffusion of substances in and out of cells

Rate of diffusion is affected by?

Surface area available

Temperature

Concentration

distance

Diffusion

the natural, passive movement of particles (atoms, molecules, ions) from a high-concentration area to a low-concentration area

Surface area-to-volume ratio

Organism made of many small cells has an advantage over an organism composed of fewer, larger cells because it has a higher surface area-to-volume ratio

As a cell’s size increases, its volume increases much more rapidly than its surface area

Some cells overcome limitation by being long and skinny

Microscopes

essential tools for viewing objects too small for the naked eye

most are less than 50 μm in diameter

Resolution

minimum distance two points can be apart and still be distinguished as two separate points

Objects must be 100 μm apart for naked eye to resolve them as two objects rather than one

Light Microscopes

Use magnifying lenses with visible light

Resolve structures that are 200 nm apart

Limit to resolution using light

Can view cells

Electron microscopes

Resolve structures that are 0.2 nm apart

Can see organelles and virus

Use beam of electrons

Low Mag.

eyepiece: 10x ; objective 4x

Medium Mag.

100x

High Mag.

400x

Oil Mag.

1000x

Low FV

4.5 mm/4500 μm

Med FV

1.8 mm/1800 μm

High FV

0.45 mm/ 450 μm

Oil FV

0.18mm/180 μm

Transmission electron microscopes

 transmit electrons through the material

Scanning electron microscpoes

beam electrons onto the specimen surface

Structural similarities of Cells

Nucleoid or nucleus where DNA is found

Cytoplasm

Ribosomes

Plasma membrane

Prokaryotic Cells

Simplest organisms

Lack a membrane-bound nucleus

Cell wall outside of plasma membrane

Do contain ribosomes

Do not contain membrane bound organelles

2 Domains of Prokaryotes:

Archaea (lack peptidoglycan) and Bacteria (have peptidoglycan)

Bacterial Walls

Most bacterial cells are encased by a strong cell wall composed of peptidoglycan

Protect the cell, maintain its shape, and prevent excessive uptake or loss of water

Susceptibility of bacteria to antibiotics often depends on the structure of their cell walls

Flagella

Present in some prokaryotic cells

• May be one or more or none

Used for locomotion

Rotary motion propels the cell

Eukaryotic Cells

Possess a membrane-bound nucleus

More complex than prokaryotic cells

Hallmark is compartmentalization

• Achieved through use of membrane-bound organelles and endomembrane system

Possess a cytoskeleton for support and to maintain cellular structure

Nucleus

• Repository of the genetic information

• Most eukaryotic cells possess a single nucleus

• contain Nucleolus

• Nuclear envelope

  • 2 phospholipid bilayers

  • Nuclear pores – control passage in and out

• In eukaryotes, the DNA is divided into multiple linear chromosomes

  • Chromatin is chromosomes plus protein

Nucleolus

region where ribosomal RNA synthesis takes place

in the middle of the nucleus

Nuclear envelope

a double-membrane barrier in eukaryotic cells that encloses the nucleus, separating its genetic material (chromosomes) from the cytoplasm, and is crucial for regulating transport via nuclear pores

2 phospholipid bilayers

Nuclear pores

large, complex protein channels in the nuclear envelope that act as selective gateways

control passage in and out

Chromatin

the substance in cell nuclei made of DNA tightly wound around proteins (histones) to form a complex that fits the long DNA strands into a compact structure, allowing for organization, replication, and gene regulation.

Histones

fundamental proteins that organize DNA into compact structures called chromatin

form nucleosomes (histones wrapped around DNA)

Ribosomes

Cell’s protein synthesis machinery

Found in all cell types in all 3 domains

Ribosomal RNA (rRNA)-protein complex

Protein synthesis also requires messenger RNA (mRNA) and transfer RNA (tRNA)

Ribosomes may be free in cytoplasm or associated with internal membranes

Endomembrane system

Series of membranes throughout the cytoplasm

Divides cell into compartments where different cellular functions occur

One of the fundamental distinctions between eukaryotes and prokaryotes

Endoplasmic reticulum

protein/lipid synthesis, folding, modification, and transport

Rough endoplasmic reticulum (RER)

Attachment of ribosomes to the membrane gives a rough appearance

Synthesis of proteins to be secreted, sent to lysosomes or plasma membrane

Chromosomes

groups of chromatin

Smooth Endoplasmic reticulum

Relatively few bound ribosomes

Variety of functions – synthesis, store Ca²⁺, detoxification

Calcium

drives cellular activity

Golgi apparatus

Flattened stacks of interconnected membranes (Golgi bodies)

Functions in packaging and distribution of molecules synthesized at one location and used at another within the cell or even outside of it

Has cis and trans faces

Vesicles transport molecules to destination

Vesicles

membrane bound package

Lysosomes

Membrane-bounded digestive vesicles

Arise from Golgi apparatus

Enzymes catalyze breakdown of macromolecules

Destroy cells or foreign matter that the cell has engulfed by phagocytosis

Microbodies

Variety of enzyme-bearing, membrane-enclosed vesicles 

Peroxisomes

Peroxisomes

Contain enzymes involved in the oxidation of fatty acids

Hydrogen peroxide produced as by-product – rendered harmless by catalase

Vacuoles

Membrane-bound structures in plants

Various functions depending on the cell type

There are different types of vacuoles:

• Central vacuole in plant cells

• Contractile vacuole of some fungi and protists

• Storage vacuoles

Mitochondria

• Found in all types of eukaryotic cells

• Bound by membranes

  • Outer membrane

  • Intermembrane space

  • Inner membrane has cristae(increase surface area)

  • Matrix

• On the surface of the inner membrane, and also embedded within it, are proteins that carry out oxidative metabolism

• Have their own DNA

Chloroplasts

Organelles present in cells of plants and some other eukaryotes

Contain chlorophyll for photosynthesis

Surrounded by 2 membranes

• Thylakoids are membranous sacs within the inner membrane

  • Grana are stacks of thylakoids

Have their own DNA

Thylakoids

membrane-bound sacs inside the stroma of chloroplasts (and cyanobacteria) that house chlorophyll and other pigments

Stroma

the gel-like, fluid-filled space surrounding the thylakoids

Innermost region of chloroplast

Contains DNA,ribosomes, and enzymes

Grana

he stacks of thylakoids embedded in the stroma of a chloroplast.

Endosymbiosis

Proposes that some of today’s eukaryotic organelles evolved by a symbiosis arising between two cells that were each free-living

One cell, a prokaryote, was engulfed by and became part of another cell, which was the precursor of modern eukaryotes

Mitochondria and chloroplasts

Cytoskeleton

Network of protein fibers found in all eukaryotic cells

• Supports the shape of the cell 

• Keeps organelles in fixed locations

Dynamic system – constantly forming and disassembling

Microfilaments (actin filaments)

Two protein chains loosely twined together

Movements like contraction, crawling, “pinching”

Microtubules

Largest of the cytoskeletal elements

Dimers of α- and β-tubulin subunits

Facilitate movement of cell and materials within cell

Intermediate filaments

Between the size of actin filaments and microtubules

Very stable – usually not broken down

providing mechanical strength, maintaining cell shape

Actin

Motor protein fibers that ratchet and cause pulling and movement

thin

myosin

in skeletal muscle cells

actin attach to and pull muscle cells fibers closer together causing concentric contractions

dense

pseudopodia

temporary arm/protrusion on amoeboid cell surface for movement and feeding

cytoplasmic streaming

when substances move across cytoplasm quickly along cytoskeleton

Centrosomes

Region surrounding centrioles in almost all animal cells

Microtubule-organizing center

• Can nucleate the assembly of microtubules

Animal cells and most protists have centrioles – pair of organelles

Plants and fungi usually lack centrioles

Tight junction

• Connect the plasma membranes of adjacent cells in a sheet – no leakage

• in animals

Anchoring junction

• Mechanically attaches cytoskeletons of neighboring cells (desmosomes)

Communicating junction

Chemical or electrical signal passes directly from one cell to an adjacent one (gap junction, plasmodesmata)

Plasmodesmata

Specialized openings in their cell walls

Cytoplasm of adjoining cells are connected

Function similar to gap junctions in animal cells

in plants

Prokaryotic Ribosomes

Large subunit-50S

Small subunit-30S

Total-70S

Eukaryotic Ribosomes

Large subunit-60S

small subunit-40S

Total subunit-80S