AP Biology Unit 2: Cells

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Cells

the basic structural and functional units of every organism

What 4 things do all cells have?

1. They are bound by a plasma membrane

2. They contain cytosol

3. They contain ribosomes

4. They contain chromosomes

What is a plasma membrane?

any membrane in a cell

What is a cell membrane?

membrane surrounding the cell

What is the difference between a plasma membrane and a cell membrane?

plasma membrane is a wider term

What is the difference between cytosol and cytoplasm?

cytosol is just the liquid, cytoplasm is the liquid with the organelles

What are the two types of cells?

prokaryotes and eukaryotes

What are characteristics of prokaryotes? (hint: there are 6)

• Domains Bacteria and Archaea

• DNA is in the nucleoid region

• Generally smaller in size than eukaryotes (there are a few exceptions)

• Lack internal membrane bound organelles

• Circular chromosomes

• Multicellular

What is Archaea?

form of bacteria that prefers extreme environments

What are membrane bound organelles?

organelle with its own plasma membrane

What are characteristics of eukaryotes? (hint: there are 5)

• Protists, Fungi, Animals, Plants

• DNA is in the nucleus

• Contain membrane bound organelles that compartmentalize cellular functions (keeps reactions separate into different cytosols of organelles)

• Linear chromosomes

• Unicellular

Organelles

membrane bound structures in eukaryotes

What are the two classifications of organelles?

endomembrane system, energy organelles

Endomembrane System

organelles and subcellular components that interact (directly or via vesicles) to modify, package, and transport polysaccharides, proteins, and lipids in the cell

What organelles are part of the endomembrane system? (hint: there are 6)

1. Nuclear envelop

2. Endoplasmic reticulum (ER)

3. Golgi complex

4. Lysosomes

5. Vesicles/vacuoles

6. Plasma membrane

Energy Organelles

convert energy to forms that cells can use for work

What are the two types of energy organelles?

1. Mitochondria

2. Chloroplasts

What are the two functions of compartmentalization?

1. Increases surface area for reactions to occur

2. Prevents interfering reactions from occurring in the same location

Where does compartmentalization occur?

eukaryotes and membrane-bound organelles

Do prokaryotes have compartmentalization?

No

Compartmentalization

different metabolic processes and enzymatic reactions occur in different locations

What cell components are unique to plants? (hint: there are 4)

• Chloroplasts

• Central vacuole

• Cell wall

• Plasmodesmata

What cell components are unique to animals? (hint: there are 3)

• Lysosomes

• Centrosomes

• Flagella

Do animal cells have a central vacuole?

No. Although animal cells have a vacuole, they do not have a central vacuole.

Plasmodesmata

holes in the cell wall, uses for cell communication and transport

The nucleus contains ________ material

genetic

What does the nuclear envelope do?

transports things around the cell

What are characteristics of the nuclear envelop? (hint: there are 3)

• double membrane

• has pores

• continuous with the ER membrane (membrane connects to ER)

What do pores do?

regulate entry and exit of materials from the cell

Nucleolus

dense region of the nucleus where ribosomal RNA (rRNA) is synthesized

What is the function of the nucleolus?

makes ribosomes

rRNA

ribosomal RNA

rRNA is combined with ________ to form large and small subunits of ________

proteins, ribosomes

subunits of ribosomes exit via ________ ______ and then assemble into ________

nuclear pores, ribosomes

Can RNA be double stranded?

yes, but it is not common

DNA → RNA → protein

transcription and translation

What are ribosomes comprised of?

ribosomal RNA (rRNA) and protein

What is the function of ribosomes?

synthesize proteins

Where can ribosomes be found? (hint: there are two)

1. Cytosol

2. Bound to the ER or nuclear envelope

What are ribosomes in the cytosol called?

“free ribosomes” because they just float around the cytosol

If ribosomes are produced in the __________ ____________ or __________ _____________ they can be secreted from the cell via transport vesicles.

endoplasmic reticulum (ER), nuclear envelope

Endoplasmic Reticulum (ER)

a network of membranous sacs and tubules

What are the membranous sacs in the ER caled?

cisternae

What are the functions of the ER? (hint: there are 2)

• Provides mechanical support by helping cells maintain shape

• Intracellular transport (transport within the cell)

What are the two types of ER?

rough ER, smooth ER

What is the main difference between the rough ER and smooth ER?

rough ER contains ribosomes bound to the ER membrane and smooth ER contains no ribosomes

What is the function of the rough ER?

compartmentalizes protein synthesis

What are the functions of the smooth ER? (hint: there are 2)

• synthesizes lipids

• detoxifies the cell

What does the golgi complex contain?

flattened membranous sacs called cisternae

What are the two faces of the golgi complex called that gives it directionality?

• cis face

• trans face

What is the function of the cis face of the golgi complex?

receives vesicles from the ER

What is the function of the trans face of the golgi complex?

sends vesicles back out into the cytosol to other locations or to the plasma membrane for secretion

What are the functions of the golgi complex? (hint: there are 5)

• receives transport vesicles with materials it receives from the ER

• modifies the materials

• sorts the materials

• adds molecular tags

• packages materials into the new transport vesicles that exit the membrane via exocytosis

What is an analogy for the golgi complex?

The golgi is like UPS. It does not make materials. It only modifies, sorts, packages, and ships.

Lysosomes

membranous sac with hydrolytic (relating to or caused by hydrolysis) enzymes

Where are lysosomes?

animal cells

What are the functions of lysosomes? (hint: there are 3)

• Hydrolyzes (digests/breaks down) macromolecules

• Autophagy

• Plays a role in apoptosis

Autophagy

• lysosomes can recycle their own cell’s organic materials and organelles that are not functioning properly

• it allows a cell to renew itself

Apoptosis

programmed cell death, not just anytime a cell dies

How do lysosomes play a role in apoptosis?

the membrane becomes permeable → releases enzymes into the cytoplasm → breaks down cellular components

What are the steps in autophagy?

1. A membrane forms around the cellular component targeted for degradation (forms a bubble around it so the lysosome knows where to go)

2. Membrane engulfs cellular components

   1. Forms a structure called an autophagosome

3. Fuses with lysosome

4. Hydrolytic enzymes in lysosomes digest the organelles and their components are recycled

   1. Amino acids and other small molecules are released back into the cytoplasm

Peroxisomes

membrane bound metabolic compartment, NOT apart of the endomembrane system

What are the functions of peroxisomes? (hint: there are 4)

• Catalyze reactions that produce hydrogen peroxide (H₂O₂)

• Break down fatty acid molecules

• Synthesize certain phospholipids

• Detoxify compounds

What is the function of hydrogen peroxide (H₂O₂)?

to detoxify certain compounds, can damage the cell if any escapes

How do peroxisomes differ from the smooth ER or lysosomes?

peroxisomes detoxify using only hydrogen peroxide (H₂O₂)

Catalase

enzyme in peroxisomes

What does catalase do?

breaks down hydrogen peroxide (H₂O₂) into water and oxygen

Vacuoles

vesicles that stem from the ER and Golgi

Vesicles

• membrane bound sacs that help in transport

• usually temporary

• selective in transport

What are the characteristics of vacuoles in animal cells? (hint: there are 3)

• small in size = more per cell

• assist in endocytosis/exocytosis processes

• store cellular materials

What are the characteristics of vacuoles in plant cells? (hint: there are 3)

• central vacuole; large in size

• stores nutrition and water (important for turgor pressure)

• can function like lysosomes

Turgor Pressure

more water = firm upright plant

What is the main difference between a vacuole in plant cells vs. animal cells?

plant cells have a large central vacuole, while animal cells have smaller vacuoles

What is the first step of protein synthesis and what occurs in it?

Step 1: Transcription and RNA Processing

1. Transcription

2. mRNA undergoes processing to prepare for translation

3. Processed mRNA exits the nucleus through nuclear pores

Transcription

DNA sequence of a gene is copied into messenger RNA (mRNA)

What does mRNA serve as?

a template that will be used to assemble a protein

What is the second step of protein synthesis and what occurs in it?

Step 2: Translation

1. mRNA leaves the nucleus and is translated by ribosomes

2. mRNA that codes for proteins destined for secretion, insertion into the cell membrane, or lysosomes, is translated by ribosomes bound to the rough ER and sent to the Golgi

3. mRNA that codes for proteins that will function in the cytosol is translated by free ribosomes in the cytoplasm and then discharged in the cytoplasm

4. After translation, the polypeptide chain begins to fold into a specific 3D shape

5. rough ER packages the protein into vesicles

Translation

the process where ribosomes reads the mRNA sequence and translate it into a polypeptide chain

Polypeptide Chain

sequence of amino acids

What is the third step of protein synthesis and what occurs in it?

Step 3: Folding and Modification

1. vesicles from the RER travel to the cis face of the Golgi

2. In the Golgi, the protein undergoes the addition of sugar groups or cleavage of the peptide chain

3. Modified protein is packaged into vesicles

4. Vesicles bud off from the trans face

What is the foruth step of protein synthesis and what occurs in it?

Step 4: Secretion or Use in the Cell

1. Vesicles containing the modified proteins can either:

   1. Fuse with the plasma membrane to create the proteins outside the cell via exocytosis

   2. Deliver them to specific locations within the cell where they are needed

Mitochondria

site of cellular respiration

Cristae

folds in the inner membrane of mitochondria

What is the difference between the inner membrane and outer membrane of the mitochondria?

outer membrane is smooth, inner membrane is highly convoluted (it has many folds)

What are the two functions of the cristae?

1. divides the mitochondria into two internal compartments

2. increases the surface area

Intermembrane of the Mitochondria

space between the inner and outer membrane

Mitochondrial Matrix

enclosed by inner membrane

What is the site of the Krebs cycle?

mitochondrial matrix

What does the mitochondrial matrix contain? (hint: there are 3)

• enzymes that catalyze cellular respiration and produce ATP

• mitochondrial DNA

• ribosomes

What does the number of mitochondria in a cell correlate with?

metabolic activity

How does the number of mitochondria in a cell correlate with metabolic activity?

cells with high metabolic activity have more mitochondria (cells that move/contract)

Chloroplast

specialized organelles in plants and photosynthetic algae

What is the site of photosynthesis?

chloroplast

What contains the green pigment chlorophyll?

chloroplast

What two things are inside the double membrane of chloroplasts?

1. Thylakoids

2. Stroma

Thylakoids

membranous sacs that can organize into stacks called grana

Where do light dependent reactions occur?

grana

Stroma

fluid around thylakoids

What is the location for the Calvin cycle?

stroma

What does the stroma contain? (hint: there are 3)

• Chloroplast DNA

• Ribosomes

• Enzymes