1.3 The Cell Flashcards
What is a cell?
simplest self-reproducing entity that can exist as an independent unit of life
Describe different cell sizes.
- cells that make up layers of skin are ~100 mcirometers, or 0.1 mm, in diameter
- many bacteria are less than a micrometer long
- some nerve cells in humans extend slender projections known as axons for distances as great as a meter
- cannonball-size egg of an ostrich is a single giant cell
What is the stable blueprint of information in molecular form that all cells contain?
- have a discrete boundary that separates the interior of the cell from its external environment
- they have the ability to harness materials and energy from the environment
What do nucleic acids do?
store and transmit information needed for growth, function, and reproduction
What is the first essential feature of a cell?
its ability to store and transmit information
How do cells accomplish its ability to store and transmit information?
cells require a stable archive of information that encodes and helps determine their physical attributes
organisms require an accessible and reliable archive of information that helps determine their structure and metabolic activities
How do cells reproduce?
cells must be able to copy their archive of information rapidly and accurately
in all organisms, the information archive is remarkable molecule known as DNA
What is DNA?
a double-stranded helix, with each strand made up of varying sequences of four different kinds of molecules connected end to end
What makes DNA special?
the arrangement of the four different kinds of molecular subunits, they provide a four-letter alphabet that encodes cellular information
What does the information encoded in DNA direct?
the formation of proteins, the key structural and functional molecules that do the work of the cell
What part of a cell depends on proteins?
internal architecture
shape
ability to move
various chemical reactions
How does the information stored in DNA direct the synthesis of proteins?
first, existing proteins create a copy of the DNA’s information in the form of a closely related molecule called RNA
What is RNA?
ribonucleic acid
- a molecule chemically related to DNA that is synthesized by proteins from a DNA template
What is transcription?
the synthesis of RNA from a DNA template, the copying of information from one form into another
What is translation?
after transcription, specialized molecular structures within the cell then “read” the RNA molecule to determine which building blocks to use to create a protein
translation converts information stored in the language of nucleic acids to information in the language of proteins
What is the central dogma of molecular biology?
the idea that information flows from nucleic acids to proteins, but not in the opposite direction
the view that information transfer in a cell usually goes from DNA to RNA (specifically mRNA) to protein
*figure 1.13 textbook
What does the central dogma describe?
the basic flow of information in a cell and, while there are exceptions, it constitutes a fundamental principle in biology
How are specific segments of DNA defined?
as proteins are ultimately encoded by DNA, we can define specific segments of DNA according to the proteins that they encode
What is a gene?
stretch of DNA that affects one or more traits in an organism, usually through an encoded protein or noncoding RNA
What is replication?
process of copying DNA so genetic information can be passed from cell to cell or from an organism to its progeny
What does DNA’s double-stranded helical structure allow?
each organism’s DNA can be stably and reliably passed from generation to generation
What happens to the double helix during replication?
each strand of the helix serves as a template for a new strand
Why is replication necessarily precise and accurate?
because mistakes introduced into the cell’s information archive may be lethal to the cell
errors in DNA can and do occur during the process of replication, and environmental insults can damage DNA as well
What are mutations?
any heritable change in genetic material, usually a change in the nucleotide sequence of a gene
they can spell death for a cell, or they can lead to the variations that underlie the diversity of life and the process of evolution
What is the second essential feature of all cells?
a plasma membrane that separates the living material within the cell from the nonliving environment around it
*figure 1.14 textbook
Describe the plasma membrane.
- there is an active and dynamic interplay between cells and their surroundings that is mediated by the plasma membrane
- all cells require sustained contributions from their surroundings, both simple ions and the building blocks required to manufacture macromolecules, they also release waste products into the environment
- controls the movement of materials into and out of the cell
What do cells have internally?
internal membranes that divide the cell into discrete compartments, each specialized for a particular function
What is the nucleus?
compartment of the cell that houses the DNA in chromosomes
What does the nuclear membrane do?
like the plasma membrane, it selectively controls movement of molecules into and out of it
What is cytoplasm?
contents of the cell other than the nucleus, space outside the nucleus
What are prokaryotes?
cells without a nucleus
most are single-celled organisms, some have simple multicellular forms
What are eukaryotes?
cells with a nucleus
exist as single cells or multicellular organisms
What do prokaryotes do?
- some live in peaceful coexistence with humans, inhabiting out gut and aiding digestion
- others cause disease - salmonellosis, tuberculosis, and cholera are familiar examples of such bacterial diseases
What does the success of prokaryotes depend on?
depend in part on their small size, their ability to reproduce rapidly, and their ability to obtain energy and nutrients from diverse sources
What do muscle cells do?
contract
What do red blood cells do?
carry oxygen to tissues
What do skin cells do?
provide an external barrier
What are the 3 domains of life?
Bacteria, Archaea, and Eukarya
What are Bacteria and Archaea?
mostly single-celled microorganisms that lack a nucleus and are therefore prokaryotes
many Archaea flourish under seemingly hostile conditions, such as those found in the hot springs of Yellowstone national Park
What are Eukarya?
have a nucleus and are eukaryotic
What is a third key feature of cells?
the ability to harness energy from the environment
Where do organisms acquire energy from?
two sources:
- sun
- chemical compounds
What is metabolism?
chemical reactions occurring within cells that convert molecules into other molecules and transfer energy in living organisms
the term describes chemical reactions by which cells convert energy from one form to another and build and break down molecules
these reactions are required to sustain life
Where does ATP come from from organisms?
regardless of their source of energy, all organisms use chemical reactions to break down molecules and in the process, release energy stored in a chemical form called adenosine triphosphate
What does ATP do?
enables cells to carry out all sorts of work, including growth, division, and moving substances into and out of the cell
What is a virus?
- genetic material that requires a cell to carry out its functions
- an agent that infects cells
- usually smaller and simpler than cells
Why aren’t viruses the smallest unit of life?
consider the three essential features of cells (capacity to store and transmit info, selectively permeable membrane, ability to harness energy from the environment)
have a stable archive of genetic information, DNA or RNA, surrounded by a protein coat and sometimes a lipid envelope BUT viruses cannot harness energy from the environment
therefore, on their own, viruses cannot read and use the information contained in their genetic material, nor can they regulate the passage of substances across their protein coats or lipid envelopes the way cells do
to replicate, they require a cell
How does a virus infect a cell?
by binding to the cell’s surface, inserting its genetic material into the cell, and, in most cases, using the cellular machinery to produce more viruses
they can then lyse, or break, the cell, enabling the new viruses to seek out and infect more cells
in some cases, genetic material of the virus becomes integrated into the DNA of the host cell
