IB Biology - Cell Structure

Explain why cells with different functions have different structures

Different organisms have developed unique structures that perform their functions, and do so in a way that is suitable for their specific environments

Cell theory:

• all living organism composed of cells

• cells are the smallest unit of life

• cells come only from other cells

All cells have…

Cell membrane, DNA and cytoplasm

Eye piece graticule:

does not change and is dimension less

Stage micrometer:

mini ruler for microscope (usually used to calculate graticule divisions0

Optical Light microscope:

• small and easy to carry

• no vaccum needed

• simple smaple prep

• Mag = x2000

• res = 200nm

• specimen can be living or dead

• Eukaryotic nuclei, mitochondria, chloroplasts

Electron microscope (general)

• large and cant be moved

• vaccum needed

• complicated prep

• mag = x500000

• res = 0.5nm

• specimens need to be dead

• organelles, viruses, DNA

Transmission vs Scanning EMs

TEM:

+ves:

• high resolution

• internal structures can be seen

-ves:

• only thin AND dead specimen

• long prep

• NO COLOUR

SEM:

+ves:

• 3d/ thick specimen okay

• external structure

-ves:

• low resolution

• Dead specimen

• NO COLOUR

Electron microscope developments:

Cryogenic electron microscopy:

• flash freezing solutions w proteins

• frozen sol. is then exposed to electrons to produce images of molecules

Freeze fracture (EM):

• rapidly frozen sample using liquid nitrogen and physically broken apart in a vaccum

• cross section

Optical microscope discoveries:

Condenser: lenses that help direct light from the source

Fluorescent dyes: used to combine w specific cell strcutures when exposed to UV

Immunofluorescence: when antibodies r prepped with dyes and bind w traget molecules complimentary to the antibody

Draw the ultra structure of E. Coli as seen in an electron micrograph

.

Draw and label a diagram of the ultra structure of a generic plant cell

.

Draw and label a diagram of the ultra structure of a generic animal cell

.

Draw a labeled diagram of a palisade cell from the leaf mesophyll

.

State structural differences between plant and animal cells.

• Chloroplasts: Plants may have them, animals do not

• Cell walls: Plants have them, animals don't

• Vacuoles: Plant cells have large and central vacuoles, animal cells have small and temporary ones (if they have any)

• Cholesterol: Plant cells don't have them, animal cells have them in plasma membranes

• Excess Glucose: Plant cells store as starch, animals store as glycogen

What are the similarities between eukaryotic and prokaryotic cells?

• both have a cell memebrane,

• cytoplasm and

• genetic material

What is the structure of lysosomes?

• Membranous sacs filled with hydrolytic enzymes, which catalyzes the breakdown or proteins, nucleic acids, lipids, and carbohydrates.

• Lipid layer

What is the function of lysosomes?

Breakdown of food or unwanted/ damaged substances or hydrolysis of macromolecules occurs in lysosomes

What is the structure of a cell wall?

• made of cellulose (plants), peptidoglycan (prokaryotes) and chitin (fungi)

• permeable

• strong

What is the function of the cell wall in plants?

Provides support and mechanical strength. Prevents excess water uptake

What is the function of the vacuole?

It maintains hydrostatic pressure

What is the structure of a vacuole

It's the fluid-filled internal cavity surrounded by a membrane. It's usually formed from the Golgi apparatus

What is the function of chloroplast?

• Site of photosynthesis, as the first step of photosynthesis is the absorption of light- produced glucose

What is the structure of chloroplast in plants?

• Double membrane

• Thykloid stacks (Granum)- where chlorophyll photosynthesises

• DNA strand

• 70S ribosomes

• Stroma (cytoplasm)

• starch grain

What is the function of mitochondria?

It's the site of aerobic respiration (ATP production)

What is the structure of the mitochondria?

Double membrane structure, where the outer membrane is smooth and the inner membrane is folded into cristae (singular christa)

What is the function of the golgi apparatus?

It's involved in sorting, storing, modification, and export of materials synthesized in the cell

What is the structure of a golgi apparatus?

Assembly of vesicles and folded membranes located near the cell membrane

What is the function of the endoplasmic reticulum?

It transports materials between organelles. For smooth ER, that's lipids. For a rough ER, that's proteins

What is the structure of the endoplasmic reticulum?

Membrane network that may be bare (smooth ER) or studded with ribosomes on its exteriors (rough ER)

What is the function of a nucleus?

It stores genetic material (DNA) as chromatin, and is the site of ribosome assembly

What is the structure of a nucleus?

It's a double membrane structure with pores. The membrane allows compartmentalization of eukaryotic DNA, providing an area where DNA can carry out its functions without being affected by processes happening in other areas of the cells.

What is the function of a plasma membrane?

Semi-permeable and selective barrier surrounding the cell

What is the structure of a plasma membrane?

It's a phospholipid bilayer embedded with proteins.&

What is the function of a cytoskeleton?

Provides internal structure and mediates intercellular transport

What is the structure of a cytoskeleton?

Filamentous scaffolding within the cytoplasm

What is the function of ribosomes?

Ribsosomes are the site of protein synthesis

What is the structure of Ribosomes?

Complexes of RNA and protein. They may be free in the cytoplasm or attached to the surface of the endoplasmic reticulum

What is the difference in structure between ribosomes in eukaryotes and prokaryotes?

Larger in eukaryotes (80S) than prokaryotes (70S)

What are organelles?

Specialized sub-structures within a cell that serves a specific function.

Which 4 kingdoms can eukaryotic cells be divided into?

Protista, fungi, plantae, and animalia

What are eukaryotic cells compartmentalized by?

Membrane-bound structures (organelles)

What is believed to have evolved from prokaryotic cells?

Eukaryotic cells, via endosymbiosis

What is the summary of distinguishing characteristics of prokaryotic cells in comparison to eukaryotic cells?

DNA is not enclosed within a membrane, and forms one circular chromosome

Lacks membrane-bound organelles

Cell wall is made up of a compound called peptidoglycan

Undergoes binary fission
Characteristically small, usually 1 to 5 micrometers

What is the process of binary fission?

DNA is copied, and 2 daughter chromosomes become attached to different regions on the plasma membrane. The cell then divides into 2 genetically identical daughter cells

What is binary fission?

Asexual reproduction, when prokaryotic cells divide

What is a prokaryotic flagella and what is its function?

Flagella are long, slender projections that contain a motor protein that enables movement

What is a cytoplasm in prokaryotic cells?

Internal fluid component

What is a prokaryotic capsule and what is its function?

A capsule is a thick polysaccharide layer that is used for protection against desiccation and phagocytosis

What is a prokaryotic Plasmid?

Plasmid is an autonomous circular DNA molecules that may be transferred between bacteria (horizontal gene transfer)

What is the function of a prokaryotic Nucleoid region?

Region of cytoplasm where DNA is located. It's non-compartmentalized, and is involved with cell control and reproduction

What is the function of a prokaryotic Ribosomes?

Prokaryotic ribosomes are complexes of RNA and protein that are responsible for polypeptide synthesis

What does the prokaryotic pili do?

Pili's main function is joining the bacterial cells in preparation for transfer of DNA from one cell to another (sexual reproduction)

Also enables adherence to surfaces (attachment pili)

Where is the prokaryotic cell membrane found in?

Just inside the cell wall

What is the function of a prokaryotic cell membrane?

Prokaryotic cell membrane controls movement of materials into and out of cells, plays a role in binary fission of prokaryotic cells.

Semi-permeable and selective barrier surrounding the cell

What is the function of a prokaryotic cell wall?

Prokaryotic cell wall protects and maintains the shape of the cell. Prevents bursting (lysis)

What are the features of prokaryotic cells?

Cytoplasm, nucleoid, plasmid, ribosomes, cell membrane, cell wall, capsule, flagella, pili

What are the distinguishing characteristics of prokaryotic cells from eukaryotic cells?

DNA forms one circular chromosome

DNA isn't attached to any proteins

No nucleus

70S ribosomes

Reproduces via binary fission

Size is from around 1-5 micrometers

How does the process of binary fission work?

DNA is copied in response to a replication signal. Two daughter chromosomes become attached to different regions on the plasma membrane, and the cell divides into two genetically identical daughter cell

How do prokaryotes divide?

By binary fission

What components do prokaryotic cells contain?

Cytoplasm, nucleoid, plasmids, 70S ribosomes, cell membrane, cell wall, capsule, flagellum, pili

Which two distinct domains are prokaryotes classified in?

Archaebacteria and eubacteria

Which kingdom do prokaryotes belong in?

Monera

What are prokaryotes?

Organisms whose cells lack a nucleus

What is Endosymbiotic theory?

• claims that chloroplasts and bacteria evolved from prokaryotes

• when a larger prokaryote engulfed a aerobically respiring smaller prokaryote and a photosynthesisng smaller prokaryote

• Mitchondria and Chloroplast have Prokaryotic features such as:

  • Circular DNA

  • 70s ribosomes

  • double membrane