Topic 2: The Evolution and Origin of Cells

how did the initial macromolecules form?

simple organic molecules could form spontaneously and polymerize into macromolecules under the conditions thought to exist in primitive Earth's atmosphere

which macromolecules was the first self replicating molecule with genetic information?

RNA, it is capable of catalyzing a number of chemical reactions including the polymerization of nucleotides (its own replication)

properties of RNA that support the hypothesis that it was the first self-replicating molecule

it is able to both serve as a template and catalyze its own reaction, some RNAs can fold into shapes that resemble protein enzymes which allows them to catalyze chemical reactions (ribozymes)

ribozyme

a type of RNA that can act as an enzyme

Where are ribozymes found?

in the ribosome where they join amino acids together

ribosome

complexes of RNA (rRNA) and proteins

what organisms have ribosomes?

all, because they are the sites for protein synthesis

ribosome is composed of \___

two subunits, small and large rRNA

protocell

primitive cell, the first cell

membranes are composed of \___

phospholipids (bilayer)

how did the first cell arise?

the enclosure of self-replicating RNA in a membrane composed of phospholipids

phase 1 of the appearance of cells

abiotic (non-living) synthesis of simple organic compounds such as amino acids or nitrogenous bases

phase 2 of the appearance of cells

abiotic polymerization of these simple organic compounds into macromolecules such as proteins and nucleic acids

phase 3 of the appearance of cells

emergence of a macromolecule capable of both replication and storing genetic information (RNA)

phase 4 of the appearance of cells

encapsulation of the first "living" molecule within a simple membrane to form the first primitive cell

properties and strategies of cells

1. all organisms are bacteria, archaea and eukaryotes

2. bacteria, archaea and eukaryotes differ from each other in many ways

3. there are several limitations to cell size

eukaryotes

Cells that contain nuclei

Prokaryote

Cells that do not contain nuclei

groups of prokaryotes

Bacteria and Archaea

properties of prokaryotic cells

smaller and simpler than eukaryotic cells, genomes are less complex, do not contain nuclei or cytoplasmic organelles

shape of prokaryotes

spherical, rod, spiral, diameters of 1-10μm

cyanobacteria

largest and most complex prokaryotes because they carry out photosynthesis

how many genes do bacteria and archaea have?

1000-6000 genes

bacteria and archaea DNA encodes about \_____ different proteins

5000

how do prokaryotes group?

most live as single celled organisms, though some join together to form chains, clusters or other organized multicellular structues

Prokaryote habitats

enormous range of habitats

aerobic respiration

Respiration that requires oxygen, use oxygen to oxidize food molecules

anerobic respiration

Respiration that does not require oxygen (killed by slightest exposure to oxygen)

bacteria are surrounded by \___

cell wall

cell wall is composed of \___

polysaccharides and peptides

DNA in bateria

singular circular molecule in the nucleoid

nucleoid

region within a prokaryotic cell that contains most or all of the genetic material

cytoplasm in prokaryotes contains \___

ribosomes

ribosome function

protein synthesis

where are archaea found?

extreme environments similar to primitive earth

how do archaea resemble bacteria?

- appearance

- cellular system for metabolism and energy conversion

how do archaea resemble eukaryotes?

in their machinery for holding genetic information (replication, transcription, translation)

eukaryotic cells arose as \____

a branch from archaea

similarities between bacteria and eukaryotes

both surrounded by a plasma membrane and contain ribosomes

differences between bacteria ad eukaryotes

eukaryotic cells contain a nucleus and cytoplasmic organelles while bacteria do not

largest and most prominent organelle in animal cell

nucleus

largest and most prominent organelle in plant cell

vacuole

diameter of a prokaryotic cell

1 μm

diameter of a eukaryotic cell

10-100μm

unique properties that distinguish each of the three domains of life

1. presence of membrane bound nucleus

2. use of internal membranes to segregate function

3. exocytosis and endocytosis

4. organization of DNA

5. segregation of genetic information

6. expression of DNA

endocytosis

portions of the plasma membrane invaginate are pinched off to form membrane-bounded vesicles containing substances that were previously outside of the cell

exocytosis

fusion of cellular vesicles with the plasma membrane to discharge of vesicle contents into the exterior of the cell

histones

eukaryotic DNA exists as multiple linear molecules that are complexed with large amounts of proteins

chromatins

DNA-histone complexes

bacterial DNA

single, circular molecules or chromosome associated with relatively few proteins

archaeal DNA

complexed with moderate amounts of proteins that resemble the eukaryotic histone proteins

intron

eukaryotic genes have their coding sequences interrupted by ling, noncoding, intervening sequences

bacterial and archaeal ribosomes and eukaryotic ribosomes differences

bacterial and archaeal are small (70S) whereas eukaryotic are larger (80S)

bacterial and archaeal ribosomes and eukaryotic ribosomes similarities

both have 2 subunits (one small and one large)

binary fission

in bacteria and archaea, one replicated DNA molecule and half the cytoplasm go to each daughter cell

cell division in eukaryotic cells

chromosomes are distributed equally to daughter cells by mitosis, following cytokinesis

Cytokinesis

division of the cytoplasm

expression of DNA in eukaryotic cells

transcribe genetic information in nucleus into large RNA molecules and depend on later RNA processing and transport to the cytoplasm

each mRNA encodes \___

1 polypeptide

expression of DNA in bacteria

they transcribe very specific segments of genetic information into mRNA and often a single mRNA can produce several polypeptides

surface area to volume ratio

a variable that decreases as cells grow, so that it sets a limit to the size of cells.

the cell's volume determines \___

the amount of exchange that must take place across the available surface area

why cells are so small

volume of a cell grows at a greater proportion than surface area which makes the cell unable to exchange materials when it gets to a certain size.

diffusion

Movement of molecules from an area of higher concentration to an area of lower concentration.

factors that influence why cells are small

slow diffusion rate and need for sufficient concentrations of reactants and catalysis as cell size increases,

endosymbiotic theory

proposes that plastids and mitochondria were once free living prokaryotes and became organelles of eukaryotes

outer nuclear membrane is continuous with \___

ER membrane

nuclear pore

a protein-lined channel in the nuclear envelope that regulates the transportation of molecules (proteins and RNAs) between the nucleus and the cytoplasm

nucleus origin

from archaea

cytoplasm origin

from bacteria

processes that occur in the nucleus

DNA replication and transcription to RNA, RNA processing

DNA replication

process by which a double stranded DNA molecule is copied to produce two identical DNA molecules

template for DNA replication

DNA itself

replication fork

A Y-shaped region on a replicating DNA molecule where new strands are growing

how do DNA strands open during replication?

1. initiator proteins unwind a short part of the DNA double helix

2. enzymes (DNA helicase) catalyze the disruption of the hydrogen bonds that hold the two strands of DNA together

3. single strand binding proteins coat the DNA around the replication fork to prevent the rewinding of DNA

single strand binding proteins

bind to and stabilize single-stranded DNA

DNA helicase

An enzyme that unwinds the DNA double helix during DNA replication

initiator proteins

proteins that bind to DNA and mark the point where strand separation will occur

DNA polymerase

group of enzymes that catalyze the synthesis of DNA during replication and aid in DNA repair and maintenance

DNA polymerase adds nucleotides to the \____

3' end of the strand

how many nucleotides can DNA polymerase add at one time?

one

Proofreading by DNA polymerase

mispaired nucleotide is removed by DNA polymerase

when does proofreading take place?

at the same time as DNA synthesis

DNA polymerase sites for DNA synthesis

polymerization and proofreading

The first step in the expression of genes is \____

transcription of DNA and RNA in the nucleus

transcription

process of copying a segment in a strand of DNA into a single stranded messenger RNA (mRNA)

gene

A segment of DNA on a chromosome that codes for a specific trait

gene function

encodes information to synthesize a protein

RNA poymerase

enzyme that transcribes DNA to RNA and initiates transcription