UNIT 1 Flashcards
What is cell biology?
The study of cells and their structure, function and behaviour
What is a reductionist view?
Studying the parts can explain the whole
The cell is a:
Fundamental unit of life, arises from pre-existing cell
Cells are the smallest units _
exhibiting the characteristics of LIGE
Why do we say that cells exhibit the characteristics of life?
They are able to reproduce themselves by their own efforts
Are organelles the smallest units exhibiting the characteristics of life?
Organelles are NOT the smallest units exhibiting the characteristics of life: They are NOT able to reproduce themselves by their own efforts outside of the host cell
Organelles are:
Specialized structure in a cell that performs a specific function
Are viruses the smallest units exhibiting characteristics of life?
Viruses are NOT the smallest units exhibiting the characteristics of life they are NOT able to reproduce themselves by their own efforts: they use the host reproductive machinery
The cell is:
The fundamental unit of life, the building block from which all organisms are constructed
cells –> tissues –> organs –> multicellular organisms
cells are typically __ in diameter
Cells are typically 5-20 um (0.005 - 0.02mm) in diameter
Most cells are invisible to the naked eye, so scientists:
Did not know of their existence prior to the invention of the light microscope in the 17th century
Robert Hooke’s light microscope was invented in:
1665, and later refined by Anton Leewenhoek
Convert 1m to um and nm and Angstrom units
1m = 10^6 um = 10^9 nm = 10^10A
__ is the most basic property of cells
Life
Basic properties of cells: Liife is the most basic property of cells: Cells can _ and _ in cultrure for extended periods of time
cells can grow and reproduce in culture for extended periods of time
HeLa cells are:
Cultured tumor cells isolated from a cancer patient (henrietta Lacks) by George Gray in 1951. - first human cells for extended culturing
__ are an essential tool for cell biologists
Cultured cells
What are the 10 basic properties of cells?1
- Life is the most basic property of cells
- Cells are highly complex and organized
- Cells possess a genetic program and the means to use it
4.Cells are capable of producing more of themselves - Cells acquire and utilize energy
6.Cells carry out a variety of chemical reactions, the sum of which is called metabolism - Cells engage in mechanical activities
- Cells are able to respond to stimuli
- Cells are capable of self regulation
- cells evolve
What does the 2nd basic property of cells “Cells are highly complex and organised” entail (2) ?
(1) Cellular processes are highly regulated
(2) Cells from different species share similar structure, composition, and metabolic features that have been conserved throughout evolution
What does the 3rd basic property of cells “ Cells possess a genetic program and the means to use it” entail (2) ?
(1) Genes encode information to build each cell, and the organism
(2) Genes encode information for cellular reproduction, activity and structure
What does the 4th basic property of cells “cells are capable of producing more of themselves” entail?
Cells reproduce, and each daughter cell receives a complete set of genetic instructions
What does the 5th basic property of cells “ cells acquire and utilize energy” entail (3) ?
-Photosynthesis provides fuel for all living organisms
-Animal cells derive energy from the products of photosynthesis mainly in the form of glucose
- Cell can convert glucose into ATP - a substance with readily available energy
Basic properties of cells #6: Cells carry out a variety of chemical reactions, the sum of which is called:
metabolism
Basic properties of cells #6: Cells engage in :
mechanical activities
Basic properties of cells #8: Cells are able to respond to :
stimuli
Basic properties of cells #9: Cells are capable of :
Self - regulation
Basic properties of cells # 10 : cells __
cells EVOLVE
What are the two main types of cells?
Prokaryotic and eukaryotic
Prokaryotic and eukaryotic cells can be distinguished by:
Their size and types of organelles
Prokaryotes are all ___
bacteria
Prokaryotes are all bacteria which arose __
3.7 billion years ago
Eukaryotes include:
Protists, animals, plants and fungi
All cells contain __ as a store of genetic information
All cells contain DNA (deoxyribonucleic acid) as a store of genetic information
In prokaryotic cells, DNA is ___
not segregated within a defined nucleus
In Eukaryotic cells, DNA is___
segregated within a defined nucleus
Prokaryotes comprise:
A single membrane-limited compartment
Cytoplams in prokaryotes contains:
30 000 ribosomes (the sites of protein synthesis) which account for its granular appearance)
sites of protein synthesis
ribosomes
Nucleoids are found in:
prokaryotes
Nucleoid is a:
Single circular DNA molecule which is NOT surrounded by a membrane seperating it from the cytoplasm, the region of the cell lying outside the nucleoid
In a prokaryote, the region of the cell lying outside the nucleoid
cytoplams
A typical prokaryotic cell is about __ in size
1 um
what is an example of a typical prokaryotic cell?
E. Coli
What are common features of prokaryotic and eukaryotic cells (5)?
(1) Plasma membrane of similar construction
(2) Genetic information in DNA, using identical genetic code
(3) Both store chemical energy in the form of ATP
(4) Shared metabolic pathways (glycolysis, TCA cycle)
(5) Proteasomes (for protein degradation) of similar construction)
What are proteasomes?
large protein complexes that break down proteins in cells
Do prokaryotes have membrane bound organelles ?
no
Eukaryotes:
Features of eukaryotic cells not found in prokaryotic cells (4):
(1) Nuclear envelope, separating nucleus from cytoplasm
(2) Complex chromosomes that compact into mitotic structures
(3) membrane-bound cytoplasmic organelles
(4) cytoskeleton with associated motor proteins
What are three characteristics that distinguish prokaryotic and eukaryotic cells?
(1) complexity
(2) cellular reproduction
(3) Genetic material
Distinguish prokaryotic cells from eukaryotic cells in terms of complexity:
Prokaryotes are relatively simple
Eukaryotes are more complex in structure and function
Distinguish prokaryotic cells from eukaryotic cells in terms of cellular reproduction:
Eukaryotes divide by mitosis
Prokaryotes divide by simple fission
Distinguish prokaryotic cells from eukaryotic cells in terms of genetic material - packaging
Prokaryotes have a nucleoid region
whereas
Eukaryotes have a membrane-bound nucleus.
Distinguish prokaryotic cells from eukaryotic cells in terms of genetic material - amount:
Eukaryotes have much more genetic material than prokaryotes
Distinguish prokaryotic cells from eukaryotic cells in terms of genetic material - form:
Eukaryotes have many chromosomes made of both DNA and protein (histones)
prokaryotes have a single, circular DNA with no histone proteins
Histones:
Histone proteins are proteins that help package DNA into chromosomes in eukaryotic cells.
The nucleus is the __ of the cell
The nucleus is the information store of the cell
The nucleus contains molecules of DNA (deoxyribonucleic acid) which are __
extremely long polymers that encode the genetic specification of the organism
In eukaryotes, the nucleus is surrounded by:
A double membrane, called the nuclear envelope
In eukaryotes, the nucleus communicates with the cytosol via __
nuclear pores that perforate the enveloppe
The nuclear envelope consists of (3):
(1) Two concentric membranes, called the INNER and OUTER NUCLEAR MEMBRANES
(2) The NUCLEAR LAMINA, a fibrous network that provides structural support to the nucleus
(3) NUCLEAR PORE COMPLEXES, the only channels through which molecules are able to travel between the nucleus and the cytoplasm
The nuclear lamina supports the __ and is composed of _
the nuclear lamina supports the nuclear envelope and is composed of lamins
a fibrous network that provides structural support to the nucleus
nuclear lamina
the only channels through which molecules are able to travel between the nucleus and the cytoplasm
nuclear pore complexes
The integrity of the nuclear lamina is regulated by:
phosphorylation / dephosphorylation
What are some human conditions (2) in regards to the nuclear lamina?
(1) Lamin A/C mutation causes Hutchinson-Gilford Progeria syndrome
(2) Lamin B mutation causes leukodystrophy (loss of myelin)
Hutchinson-Gilford Progeria syndrome
Lamin A/C mutation in the nuclear lamina
leukodystrophy (loss of myelin):
Lamin B mutation in nuclear lamina
Emery-Dreifuss muscular dystrophy (elbows, neck and heels become stiff, heart problems)
Mutationsinlaminbindingproteinemerin
Leukodystrophy is a condition that causes:
loss of myelin
Mutations in lamin binding protein emerin cause
Emery-Dreifuss muscular dystrophy (elbows, neck and heels become stiff, heart problems)
Model of a vertebrate nuclear pore complex (NPC). The structure consists of several parts, including
(1) a scaffold that anchors the complex to the nuclear envelope
(2) a cytoplasmic ring
(3 a nuclear ring
(4) a nuclear basket,
(5) eight cytoplasmic filaments.
Structure of Nuclear Pore Complex and its Role in Nucleocytoplasmic Trafficking: shape
- Huge complex (15-30X mass of a ribosome) that exhibits octagonal symmetry.
Structure of Nuclear Pore Complex and its Role in Nucleocytoplasmic Trafficking: channel width
20-30 nm wide
Role of phynylalanine - glycine domains in nuclear pore complex?
- FG (phenylalanine-glycine) domains form a hydrophobic sieve that blocks the diffusion of larger macromolecules (greater than about 40,000 Daltons).
Binding of GTP (activation) requires
a protein called a GEF (guanine nucleotide exchange factor)
hydrolysis of GTP to GDP (inactivation) requires
a GAP (GTPase activating protein).
Proteins synthesized in the cytoplasm are targeted for the nucleus by:
A nuclear localization signal (NLS) having basic resisdues
NLS receptors?
importin a/b heterodimer
What are the five steps for the import of proteins through the NPC
- Proteins with an NLS bind to an NLS receptor (importin a/b heterodimer)
- The protein/importin complex associates with cytoplasmic filaments
- The protein/ importin complex passes through the NPC
- …And associates with a GTPase called Ran
5.The Ran●GTP-importin b complex is transported back to the cytoplasm where Ran is converted to Ran●GDP and brought back in to the nucleus. Importin a is returned to the cytoplasm via a protein called exportin.
The outer nuclear membrane is continuous with:
The rough ER
the space between the inner and outer nuclear membranes is continuous with:
the lumen of the rough ER
What are the ribosomal subunits in prokaryotes?
50S and 30S
the assembled ribosome in prokaryotes is:
70S
What are the ribosomal subunits in eukaryotes?
60S and 40S
What is the assembled ribosome in eukaryotes?
80S
A suborganelle of the nucleus is :
the nucleolus
The nucleolus, a suborganelle of the nucleus is a factory where:
ribosomes are assembled
What are the 5 steps involved in the ribosome assembly in the nucleolus:
(1) Ribosomal proteins are imported to the nucleus from the cytoplasm
(2) These ribosomal proteins are then delivered to the nucleus and assemble on pre-rRNA (pre-ribosomal RNA)
(3) The pre-rRNA is cleaved to form several rRNAs
(4) Ribosomal proteins and rRNAs assemble to form the 40S and 60S ribosomal subunits
(5)The subunits are exported to the cytoplasm (fully assembled ribosome is too large to fit through pore, ensuring protein synthesis takes place in cytoplasm)
The complexes composed of eukaryotic DNA and proteins are
called
chromatin
Chromatin contains about __ protein as DNA
twice as much
The major proteins of chromatin are the:
histones
Histones are
Small proteins (11 to 23 kDa) containing a high proportion of basic amino acids (arginine and lysine) that facilitate binding to the negatively charged DNA molecule
What are the 5 major types of histones:
H1
H2A
H2B
H3
H4
__ are very similar among different species of eukaryotes
Histones
Chromatin also contains
an approximately equal mass of nonhistone chromosomal proteins (more than a 1000 different types)
The basic structural unit of chromatin is called the:
nucleosome
Describe (2 main parts) of the basic structural unit of chromatin called: the nucleosome
-The DNA is wrapped around an octamer of histones H2A, H2B, H3 and H4 in a NUCLEOSOME CORE PARTICLE, and sealed by histone H1. This produces a 7-fold compaction of the DNA
- Non-histone proteins bind to the LINKER DNA between nucleosome core particles
Higher-ordered structures of chromatin
Formation of 30 nm fibers are dependent upon histone interactions and further increase compaction by ~6 fold
The 30 nm fibers are then organized into 80-100 nm supercoiled loops, possibly stabilized by a protein called cohesin.
Mitotic chromosomes represent
the ultimate in chromatin compactness with a ratio of 10,000:1 (1 μm of mitotic chromosome length contains ~1 cm of non-compacted DNA).
As a cell prepares to divide into two daughter cells, its chromatin
condenses into chromosomes that can be distinguished in the light microscope
Chromosomes can be arranged in a
karyotype (a preparation of homologous pairs ordered according to size; may be used to screen chromosomal abnormalities).
karyotype
a preparation of homologous pairs ordered according to size; may be used to screen chromosomal abnormalities
Euchromatin
returns to a dispersed state after mitosis.
Heterochromatin
is condensed during interphase.
Constitutive heterochromatin
remains condensed all the time.
Constitutive heterochromatin found mostly around
centromeres and telomeres.
Constitutive heterochromatin
Consists of highly repeated sequences and few genes.
Facultative heterochromatin
inactivated during certain phases of the organism’s life (X- inactivation)
Mitochondria play a critical role
in the generation of metabolic energy in eukaryotic cells
Mitochondria play a critical role in the generation of metabolic energy in eukaryotic cells: they:
oxidize carbohydrates and lipids to produce; the basic chemical fuel adenosine triphosphate (ATP) by a process called oxidative phosphorylation
Mitochondria play a critical role in the generation of metabolic energy in eukaryotic cells
* They oxidize carbohydrates and lipids to produce the basic chemical fuel adenosine triphosphate (ATP) by a process called:
oxidative phosphorylation
ATP is used in
a variety of energy-requiring reactions within cells
Because mitochondria consume oxygen and release carbon dioxide in the course of ATP production, the entire process is called
cellular respiration, from its similarity to breathing
Depending upon the cell type and physiological conditions, mitochondria can have
different overall structures
Mitochondria can appear as
a highly branched, interconnected tubular network.
Single mitochondrion
~4 μm length
Observations of fluorescently labeled mitochondria within living cells have shown them to be
dynamic organelles capable of dramatic changes in shape
Observations of fluorescently labeled mitochondria within living cells have shown them to be dynamic organelles capable of dramatic changes in shape:
- they can (2):
fuse with one another (fusion) or split into two (fission)
The balance between fusion and fission is a major determinant of mitochondrial morphology: fission is induced by:
contact with endoplasmic reticulum (ER) tubules.
Mitochondria arise from
preexisting mitochondria by fission
Mitochondria are surrounded by
a double-membrane system, consisting of inner and outer mitochondrial membranes separated by an intermembrane space.
mitochondria:The inner membrane forms:
numerous folds (cristae).which extend into the interior (or matrix) of the organelle. Its surface area is substantially increased by its folding into cristae.
the surface area of mitochondria is substantially increased by
its folding into cristae.
The mitochondrial matrix contains (3):
- Enzymes responsible for the oxidative breakdown of carbohydrates and lipids via the citric acid cycle, and enzymes required for the expression of mitochondrial genes
- Several identical copies of circular DNA molecules (mitochondrial genome)
- Special mitochondrial ribosomes
Inner mitochondrial membrane:
The principal site of ATP synthase
Outer membrane mitochondria:
Contains enzymes that convert lipid substrates into forms that are subsequently metabolized in the matrix
Mitochondrial disorders
Disorders that are due to abnormalities in mitochondrial structure
and function most dramatically affect muscle and nerve tissues because of their high demand for ATP.
Buildup of ROS in mitochondria cause
a 10-fold increase in mutation rate of mitochondrial (mt)DNA compared to nuclear DNA. Thus, long-lived cells (nerve cells, muscle cells) may accumulate undesirable mtDNA mutations that can result in adult-onset neurological disorders (e.g. PD) and contribute to aging.
Yeast “petite” colonies arise from
loss of mitochondrial DNA. They cannot respire and hence can only utilize fermentable carbon sources (e.g. glucose) but not non-fermentable carbon sources (e.g. glycerol, ethanol).
Endosymbiont theory:
mitochondria (and chloroplasts) are derived from smaller prokaryotic cells that took up residence in a eukaryotic cell
Support for the endosymbiont theory:
- Outer membrane of bacteria and mitochondria contain porins
- Inner membrane of bacteria and mitochondria contain the lipid cardiolipin
- Mitochondria arise from pre-existing mitochondria via fission
- Mitochondria and bacteria contain a single, circular DNA
- Mitochondrial ribosomes are similar to those of bacteria (70S)
Chloroplasts resemble mitochondria in that
both contain a permeable outer membrane and a relatively impermeable inner membrane
Stroma in mitochondria is analogous to
mitochondrial matrix.
Chloroplasts:third membrane is formed by
the thylakoids (orderly stacks are called grana).
the largest and most characteristic organelles in the cells of plants
Chloroplasts:
photosynthesis
series of light-driven reactions that creates organic molecules from atmospheric carbon dioxide (CO2)
Chloroplast sperform photosynthesis during the day light hours and thereby produce
ATP and NADPH, which in turn are used to convert CO2 into sugars inside the chloroplast
for most of its ATP production, the plant relies on
an export of sugars from its chloroplasts to the mitochondria that are located in all cells of the plants.
Three of four stages in photosynthesis (the “light reactions”) take place in the thylakoid membranes:
- Absorption of light by green pigments (chlorophylls) attached to proteins
- Electron transport to generate a H+ gradient
- Synthesis of ATP and NADPH
Each photosynthetic unit contains
several hundred chlorophyll molecules.
reaction- center chlorophyll
transfers electrons to an electron acceptor.
Yeast “petite” colonies arise from
loss of mitochondrial DNA. They cannot respire and hence can only utilize fermentable carbon sources (e.g. glucose) but not non-fermentable carbon sources (e.g. glycerol, ethanol).
