chapter 3: cellular structures and functions Flashcards
q
what is the cell theory?
it states that:
- cells are the smallest, basic unit of life
- it is the basic unit of structure and function in all living organisms and is three-dimensional in nature
- all living organisms are made of cells
> living organisms can be unicellular, consisting of a single cell, or complex, multicellular organisms, consisting of billions of cells - all cells come from pre-existing cells via cell division and involces the passing of heredity information encoded in DNA from one generation to the next
what are the differences in the structure of prokaryotic and eukaryotic cells?
presence of membrane-bound organelles:
**eukaryotic cell: has true membran-bound organelles
prokaryotic cells: lacks true membrane-bound organelles
DNA structure and location:
**eukaryotic cell: DNA is linear and enclosed within a membrane-bound structure known as the nucleus
prokaryotic cells: DNA is circular, not enclosed within a membrane but lies freely in the cytoplasm in a region called the nucleoid
size of ribosome:
**eukaryotic cell: has 80S ribosomes (except mitochondria and chloroplasts, which have 70S ribosomes)
prokaryotic cells: has 70S ribosomes
what are prokaryotic and eukaryotic cells?
- organisms of the domains bacteria and archaea consists of prokaryotic cells
> organisms are known as prokaryotes
> prokaryotes are unicellular - organisms of fungi, animals, plants and protists all consists of eukaryotic cells
> organisms are known as eukaryotes
name the cells and their components from largest to smallest.
Plant cell
Animal cell
Nucleus
Bacterium
Mitochondion
Chloroplast
Lysosome
Cilium and flagellum
Microtubule
Ribosome
Microfilament
DNA molecule
Peter ate nine burgers, made carla laugh, cry and fart. Meanwhile, Roger managed DNA
describe cell fractionation
step 1: homogenisation of cells
- cells can be broken up in various ways; can be subjected to osmotic shock, ultrasonic vibration or group up in a blender
- samples of cell suspension must be kept cold so that metabolism is slowed, and autophagy ( self-digestion, sounds like autofatty-eating itself) of organells is prevented
> they must also be buddered so that pH does not change drastically, and enzymes are not denatured - these procedures break the cell surface membrane and internal membranes of the cell into fragments that immediately reseal to form small, close vesicles
> if carefully applied, the procedures leave membrane bound organells largely intact
> like nuclei, mitochondria, chloroplasts, golgi apparatus, ribosomes and lysosomes - the suspension of cells is thereby reduced to a thick homogenate that contains a variety of membrane-bound organells, each with a distinctive charge and density
step 2: differential centrifugation
- different components of the homogenate are separated by a process known as differential centrifugation
the homogenate is filters, and then placed in a centrifuge tube to be rotated at high speeds in a machine known as a centrifuge. this treatment separates cellular structures/ components by size and density. generally the larges cellular structures experience the largest centrifugal force and move the most rapidly
- at relatively low speed, large components such as nuclei sediment to form a pellet at the bottom of the centrifuge tube
- at a slightly higher speed, a pellet/ sediment of mitochondria/ chloroplasts is deposited
- at even higher speeds and with longer periods of centrifugation, first the small vesicles and then the ribosomes can be collected in the pellet/ sediment
- all these fractions are impure, but many of the contaminants can be removed by resuspending the pellet/ sediment and repeating the centrifugation procedure several times
what are some non- membrane bound organelles?
- nucleolus
- ribosomes
- centrioles
what are the membrane bound organelles?
- nucleus
- rough endoplasmic reticulum
- smooth endoplasmic reticulum
- golgi apparatus
- lysosome
- vesicles
- mitochondrion
- chloroplast
what is the endomembrane system?
- it is a group of membranes inside a eukaryotic cell
- these membranes divide the cell into functional and structural compartments, and work together to modify, package and transport lipids and proteins
organelles that are in the endomembrane system:
- rough endoplasmic reticulum
- smooth endoplasmic reticulum
- golgi apparatus
- lysosome
- vesiciles
- nuclear envelope
- cell surface membrane
- plasma membrane
structure and function of organelles in a typical eukaryotic cell
what are the structure and functions of the nucleus?
nuclear envelope
- most prominent organelle and visible under the light microscope
- consists of the nuclear envelope, nuclear pore, nucleoplasm and nucleolus
- absent in mature sieve tube cells in plants and red blood cells
- spherical in shae
**S: **
- surrounded by a nuclear envelope which is a double membrane
> the outer membrane of the nuclear envelope is continuous with the rough endoplasmic reticulum with ribosomes attached to the surface
> the inner membrane is in contact with the nucleoplasm
> each membrane is a phospholipid bilayer with proteins attached
> the nuclear envelope has numerous tiny openings called nuclear pores
**F: **
- the nuclear envelope regulates the movement of substances into and out of the nucleus via the nucleus pores
> eg. entry of histone proteins, DNA and RNA polymerase, ribosomel proteins
> eg. exit of mRNA, tRNA, ribosomal subunits
- the nuclear envelope disintegrates during prophase of mitosis, and prophase I and II of meiosis
- this is to allow the attachmet of kinetochore microtubules to centromere of chromosomes so that sister chromatids can be pulled to opposite poles of the cell at anaphase
structure and function of organelles in a typical eukaryotic cell
what are the structure and functions of the nucleus?
nucleoplasm
**S:
**- the nucleoplasm is a gel-like matrix that fills the space in the nucleus, between chromatin fibres and nucleoli
- contains nearly all the cell’s heredity material, DNA that is usually in the form of chromatin fibres> theres two types
> heterochromatin: tightly coiled and condensed thus does not allow transcription
> euchromatin: loosely coiled and condensed thus allow transcription to take place
> chromatin fibres further coil, condense into chromosomes during cell division
- it also contains proteins, ions and nucleotides
> which are materials required for synthesis of DNA and RNA
F:
- DNA in the nucleoplasm control cellular activities by regulating protein synthesis, such as synthesis of enzymes
structure and function of organelles in a typical eukaryotic cell
what are the structure and functions of the nucleus?
nucleolus
S:
- one or more nucleolus are found in the nucleoplasm
> it is a region made up of chromatin fibres that carry the ribosomal RNA (rRNA) genes
> it also contains ribosomal proteins that are imported from the cytoplasm
> it is not bound by any membrane
> the nucleolus disappears during prophase of mitosis, prophase I and II of meiosis and
> reforms during telophase of mitosis, telophase I and II of meiosis
F:
- it is the site of transcription of rRNA genes to rRNA
- the rRNA then assembles with ribosomal proteins that are imported from the cytoplasm to form the large and small ribosomal subunits, which then come together to form a ribosome
- chromatin fibres coil and condense to form chromosomes during prophase
- since the nucleolus is a region of chromatin fibres which has genes (DNA) coding for rRNA, the nucleolus disappears when all chromatin fibres coil and condense to become chromosomes
what is the structure and functions of centrioles?
structure:
- a pair of hollow cylindrical structures lying at right angles to each other
- each cylindrical structure is made of nine triplets of microtubules arranged in a ring
- each centrioles is located in a distinctly stained region of the cytoplasm known as the centrosome
> the region is also knwon as microtubule organising centre (MTOC)
functions:
- centrioles migrate to opposite poles of the cell during prophase of mitosis/ prophase I and II of meiosis
> location of the centrioles determines the polarity of the cell
- from each pair of centrioles, short microtubules develop and radiate to form an aster
> the DO NOT make asters, they organise microtubules that form the ester
- centrioles aid in spindle fibre formation during cell and nuclear division
- the spindle fibres that form then aid the alignment of the sister chromatids / chromosomes and separate sister chromatids/ chromosomes when they shorten
what are the differences between prokaryotic and eukaryotic ribosomes?
- ribosomes are present in both prokaryotic and eukaryotic cells
> but they are different in structure - in eukaryotes, each ribosome consists of a large (60S) and a small subunit (40S), making up an 80S ribosome
- ## in prokaryotes, each ribosome consists of a large (50S and a (30S) small subunit, making up an 70S ribosome
compare prokaryotic and eukaryotic ribosomes
**attachment to other organelles
**free ribosomes: not attached to the endoplasmic reticulum
bound ribosomes: attached to rough endoplasmic reticulum and nuclear envelope
function:
free ribosomes: synthesis protein for that remain or are in use in cytoplasm
bound ribosomes: synthesise proteins that are transported through the endomembrane system
> these proteins may be proteins found in vacuoles, lysosomes or proteins to be embedded in the cell membrane or secreted out of the cell
what are the structure and functions of ribosomes?
structure: each ribosome has:
- 1 messenger RNA (mRNA) binding sit at its small ribosomal subunit and
- 3 transfer RNA (tRNA) binding sites at its large ribosomal subunit
> Exit (E) site
> Peptidyl-tRNA (P) site
> Aminocacyl-tRNA (A) site
function:
holds tRNA and mRNA in close proximity for translation to take place
- exit (E) site allows the discharged tRNA (not carrying amino acid) to leave the ribosome
- Peptidyl-tRNA (P) site holds the tRNA carrying the growing polypeptide chain
- Aminoacyl-tRNA (A) site holds the tRNA carrying the next amino acid to be added to the chain
structure: contains ribozyme
- an rRNA molecule with enzymatic/ catalytic function that is complexed to the large ribosomal subunit
function:
- the ribosome is a peptidyl transferase which catalyses the formation of peptide bond between adjacent amino acids
structure: can exist as polysomes/ polyribosomes
> which refers to a cluster of ribosomes present on a strant of mRNA
function:
- carry out translation of one mRNA to synthesise proteins at a faster rate
- since many ribosomes are translating one mRNA to form many of the same polypeptide chain at the same time
