5.3 Internal Organization of Cells Flashcards
Describe the internal organization of cells.
in addition to the plasma membrane, many cells contain membrane-bound regions within which specific functions are carried out
- such cell can be compared to a large factory, each department has a specific function and internal organization that contribute to the work of the factory
What do all cells have?
plasma membrane
genetic material
What are the two classes have cells and what are they based on?
prokaryotes and eukaryotes, based on the absence or presence of a nucleus
What are prokaryotes?
organisms, including bacteria and archaeons, that lack a nucleus
*figure 5.16 textbook
What are eukaryotes?
organisms, including animals, plants, fungi, and protists that have a nucleus
*figure 5.16 textbook
What does the presence of a nucleus in eukaryotes allow?
for processes of transcription and translation to be separated in time and space
this separation allows for more complex ways to regulate gene expression than are possible in prokaryotes
What are other differences between prokaryotes and eukaryotes?
- transcription and translation differ
- the types of lipids that make up their cell membranes (mammals have cholesterol)
- in eukaryotes other than mammals, diverse sterols are synthesized and present in cell membranes, most prokaryotes do not but some synthesize compounds called hopanoids
What is cholesterol?
belongs to a group of chemical compounds known as sterols, which are molecules containing a hydroxyl group attached to a four-ringed structure
What are hopanoids?
five-ringed structures that are thought to serve a function similar to that of cholesterol in mammalian cell membranes
From an evolutionary perspective, how are the three domains of life related?
archaeons and eukaryotes are more closely related to each other than either are to bacteria
ie. archaeons share with eukaryotes many genes involved in transcription and translation, and DNA is packaged with histones in both groups
What do prokaryotic cells lack?
- nucleus
- extensive internal compartmentalization
What do prokaryotes have instead of a nucleus?
nucleoid: a structure with multiple loops formed from supercoils of DNA
DNA is concentrated in this discrete region of the cell interior
What are plasmids?
in bacteria, a small circular molecules of DNA carrying a small number of genes that replicate independently of the DNA in the bacterium’s circular chromosome
What are plasmids commonly transferred between and how?
bacteria through the action of threadlike structures known as pili, which extend from one cell to another
ie. genes for antibiotic resistance are commonly transferred this way, which accounts for the quick spread of antibiotic resistance among bacterial populations
Describe the size of prokaryotes.
- small, typically 1-2 micrometers in diameter or smaller
- this means they have a relatively high ration of SA to V, which makes sense for an organisms that absorbs nutrients from the environment
- in other words, a large amount of membrane SA is available for absorption relative to the volume of the cell that it serves
Describe the size of eukaryotes.
larger, on the order of 10 times larger in diameter than prokaryotes, and 1000 times larger in volume
What do eukaryotes have?
- nucleus
- specialized internal structures
What is the nucleus?
physical barrier separating genetical material from the rest of the cell, houses most of the cell’s DNA
What does the nuclear membrane do?
allows for more complex regulation of gene expression than is possible in prokaryotic cells
Describe the steps that eukaryotes take to instruct the synthesis of proteins.
DNA is transcribed to RNA inside the nucleus, but the RNA molecules carrying the genetic message travel from inside to outside the nucleus, where they instruct the synthesis of proteins
What are organelles?
any one of several compartments in eukaryotes that divide the cell contents into smaller spaces specialized for different functions
*figure 5.17 textbook
What does the internal array of membranes define?
compartments called organelles
What do plant cells have that animal cells don’t?
- cell wall outside the plasma membrane
- vacuoles specialized for water uptake
- chloroplasts that convert energy of sunlight into chemical energy
- intercellular connections called plasmodesmata
What is chloroplast?
an organelle in photosynthetic eukaryotes that converts energy of sunlight into chemical energy by synthesizing simple sugars
What are plasmodesmata?
channels that allow the passage of large molecules such as mRNA and proteins between neighbouring cells
What is cytoplasm?
the entire contents of a cell other than the nucleus
What is cytosol?
the jelly-like internal environment of the cell that surrounds the organelles inside the plasma membrane
