1.3 The Cell

Question 1

What is a cell?

Answer 1

simplest self-reproducing entity that can exist as an independent unit of life

Question 2

Describe different cell sizes.

Answer 2

• 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

Question 3

What is the stable blueprint of information in molecular form that all cells contain?

Answer 3

• 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

Question 4

What do nucleic acids do?

Answer 4

store and transmit information needed for growth, function, and reproduction

Question 5

What is the first essential feature of a cell?

Answer 5

its ability to store and transmit information

Question 6

How do cells accomplish its ability to store and transmit information?

Answer 6

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

Question 7

How do cells reproduce?

Answer 7

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

Question 8

What is DNA?

Answer 8

a double-stranded helix, with each strand made up of varying sequences of four different kinds of molecules connected end to end

Question 9

What makes DNA special?

Answer 9

the arrangement of the four different kinds of molecular subunits, they provide a four-letter alphabet that encodes cellular information

Question 10

What does the information encoded in DNA direct?

Answer 10

the formation of proteins, the key structural and functional molecules that do the work of the cell

Question 11

What part of a cell depends on proteins?

Answer 11

internal architecture
shape
ability to move
various chemical reactions

Question 12

How does the information stored in DNA direct the synthesis of proteins?

Answer 12

first, existing proteins create a copy of the DNA’s information in the form of a closely related molecule called RNA

Question 13

What is RNA?

Answer 13

ribonucleic acid

- a molecule chemically related to DNA that is synthesized by proteins from a DNA template

Question 14

What is transcription?

Answer 14

the synthesis of RNA from a DNA template, the copying of information from one form into another

Question 15

What is translation?

Answer 15

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

Question 16

What is the central dogma of molecular biology?

Answer 16

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

Question 17

What does the central dogma describe?

Answer 17

the basic flow of information in a cell and, while there are exceptions, it constitutes a fundamental principle in biology

Question 18

How are specific segments of DNA defined?

Answer 18

as proteins are ultimately encoded by DNA, we can define specific segments of DNA according to the proteins that they encode

Question 19

What is a gene?

Answer 19

stretch of DNA that affects one or more traits in an organism, usually through an encoded protein or noncoding RNA

Question 20

What is replication?

Answer 20

process of copying DNA so genetic information can be passed from cell to cell or from an organism to its progeny

Question 21

What does DNA’s double-stranded helical structure allow?

Answer 21

each organism’s DNA can be stably and reliably passed from generation to generation

Question 22

What happens to the double helix during replication?

Answer 22

each strand of the helix serves as a template for a new strand

Question 23

Why is replication necessarily precise and accurate?

Answer 23

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

Question 24

What are mutations?

Answer 24

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

Question 25

What is the second essential feature of all cells?

Answer 25

a plasma membrane that separates the living material within the cell from the nonliving environment around it *figure 1.14 textbook

Question 26

Describe the plasma membrane.

Answer 26

- 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

Question 27

What do cells have internally?

Answer 27

internal membranes that divide the cell into discrete compartments, each specialized for a particular function

Question 28

What is the nucleus?

Answer 28

compartment of the cell that houses the DNA in chromosomes

Question 29

What does the nuclear membrane do?

Answer 29

like the plasma membrane, it selectively controls movement of molecules into and out of it

Question 30

What is cytoplasm?

Answer 30

contents of the cell other than the nucleus, space outside the nucleus

Question 31

What are prokaryotes?

Answer 31

cells without a nucleus most are single-celled organisms, some have simple multicellular forms

Question 32

What are eukaryotes?

Answer 32

cells with a nucleus exist as single cells or multicellular organisms

Question 33

What do prokaryotes do?

Answer 33

- 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

Question 34

What does the success of prokaryotes depend on?

Answer 34

depend in part on their small size, their ability to reproduce rapidly, and their ability to obtain energy and nutrients from diverse sources

Question 35

What do muscle cells do?

Answer 35

contract

Question 36

What do red blood cells do?

Answer 36

carry oxygen to tissues

Question 37

What do skin cells do?

Answer 37

provide an external barrier

Question 38

What are the 3 domains of life?

Answer 38

Bacteria, Archaea, and Eukarya

Question 39

What are Bacteria and Archaea?

Answer 39

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

Question 40

What are Eukarya?

Answer 40

have a nucleus and are eukaryotic

Question 41

What is a third key feature of cells?

Answer 41

the ability to harness energy from the environment

Question 42

Where do organisms acquire energy from?

Answer 42

two sources: - sun - chemical compounds

Question 43

What is metabolism?

Answer 43

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

Question 44

Where does ATP come from from organisms?

Answer 44

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

Question 45

What does ATP do?

Answer 45

enables cells to carry out all sorts of work, including growth, division, and moving substances into and out of the cell

Question 46

What is a virus?

Answer 46

- genetic material that requires a cell to carry out its functions - an agent that infects cells - usually smaller and simpler than cells

Question 47

Why aren't viruses the smallest unit of life?

Answer 47

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

Question 48

How does a virus infect a cell?

Answer 48

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