Mic 101: L6 STT Eukaryotic cells

Eukaryotes The Eukaryotic Cell = “true nucleus” algae, protozoa, fungi, plants and animals up to 100μm variable sizes and shapes

Typical Eukaryotic Cell

Cell Wall  Don’t contains any peptidoglycan like prokaryotes 1.algae: wall composed of cellulose (simple polysaccharide) 2.fungi: wall composed of chitin (simplepolysaccharide) 3.Yeast: polysaccharide glucan and mannan 4.protozoa: no wall: either flexible pellicle or no covering eukaryotes that lack a wall usually have glycocalyx instead: sticky carbohydrate layer exterior to the plasma membrane for strength, attachment, and cell recognition No eukaryotes have peptidoglycan

Cell Membrane simple phospholipid bilayer: basic structure Composed of carbohydrate and sterols: resist osmotic lysis integral and peripheral proteins: transport and metabolism (enzymes) Plasma membrane used for endocytosis: can uptake particle/large molecules or soluble particles with in the cell

Projection by Membrane

Cytoplasm  -substance between the plasma membrane and the nucleus contains: -cellular components (organelles) -cytosol = fluid portion of cytoplasm -contain complex internal structure called cytoskeleton  Cytoskeleton -composed of three types of filaments that form a scaffold: 1. microfilaments 2. intermediate filaments 3. microtubules

Cytoskeleton The eukaryotic cells maintain their structure and shape by actin microfilaments, which create a network called cytoskeleton. The fibrous proteins build up filamentous structures to Form protein network in the cell. Tubulin proteins form microtubules, which are Hollow tubes to maintain cell rigidity and protein transfer. Functions: -provide support and shape of cell -movement of cytoplasm from one part of cell to other helps- 1.To distribute nutrients 2.Move cell over the surface called cytoplasmic streaming

Nucleus  large, spherical/oval  Carrying the cell’s hereditary/ genetic information  double-membrane bound structure Structure: 1.Double membrane bound Nuclear envelope 2.Tiny channels in membrane called nuclear pore allows  Nucleus to communicate with cytoplasm  Movement of substances between nucleus and cytoplasm

Nucleus Nucleoli are condensed region inside nucleus where ribosomal RNA are synthesized. The eukaryotic DNA are linear; they are single DNA molecules with millions of nuleotides Usually eukaryotic nucleus has few DNA molecules in complex arrangement with proteins. These structures are called chromosomes.

Nucleus

Chromosome  Location-inside nucleus 1.Contains most cells DNA combined with histone and non-histone proteins 2.DNA is always organized 3.nucleosome = 165 bp DNA round around 8 histone proteins

Chromatin in non reproducing cell DNA and protein gives thread appearance=chromatin In reproducing cell chromatin coil short and thick rod appearance= chromosome

Chromosome Duplicated copies of chromosome are joined by a sequence of DNA called centromere, which usually binds with proteins called kinetochore during cell division. Chromatid is one single copy of the DNA molecule is a chromosome. Telomere is the terminal end of a chromosome with repetitive DNA sequence. Telomeres serve as a biological clock to determine how many times the chromosome and the cell can divide.

Centromere -located near the nucleus -important for nuclear division during mitosis -consists of two parts: 1. pericentriolar material  cytosol + protein fibers  organizes the mitotic spindle for cell division 2. pair of centrioles  2 cylinders, at right angles to each other  composed of 9+0 arrangement of microtubules  source of microtubules to form the mitotic spindle

Eukaryotic Cell Division The common method of cell division in microbial eukaryotes is Mitosis Occurs when the cell has sufficient nutrition and favorable atmosphere Complex and highly regulated, has 5 stages- prophase, pro-metaphase, metaphase, anaphase, telophase Final step of separation of the cells is called cytokinesis

Eukaryotic Cell Division When cell not dividing, it is in interphase. When has enough nutrition, cell replicates its DNA In prophase, the spindle fibre appears across the nucleus, the chromosomes organise themselves in the fiber inside the nuclear membrane In prometaphase, each chromatid attaches with kinetochore through its centromere In metaphase, the cellular energy ATP is used to pull the daughter chromatids towards the end of the spindle fibre In anaphase the spindle fiber becomes short, positioning the chromatids in two poles of the cell In telophase the new nuclear membrane appears around the poles of the spindle apparatus and spindle apparatus is disintegrated In cytokinesis, the cytoplasmic content of the cell distributes into two parts and cell membrane covers the separated components into two new cells.

Flagella and Cilia  projections used for cellular locomotion  projection few/long-flagella Algae-Euglena  Projection numerous/short-cilia Protozoa-Tetrahymena Structure:  contain cytoplasm, surrounded by plasma  Anchored in plasma membrane  internal structure: 9+2 array of microtubules; 9pairs in ring and 2 in center (straw-like tubes composed of tubulin)

Eukaryotic flagella