Cell structure and function
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CELL STRUCTURE AND FUNCTION. Despite the diversity among cells, three basic features are common to all cell types. All cells have outer boundary, an interior substance and a control region. CELL STRUCTURES. Composition: phospholipid bilayer with embedded proteins. Function:

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CELL STRUCTURE AND FUNCTION

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Cell structure and function

CELL STRUCTURE AND FUNCTION

Despite the diversity among cells, three basic features are common to all cell types. All cells have outer boundary, an interior substance and a control region.


Cell structures

CELL STRUCTURES


Plasma membrane

Composition: phospholipid bilayer with embedded proteins.

Function:

selective passage of molecules into and out of cell

PLASMA MEMBRANE


Nucleus

Composition: nuclear envelope surrounding nucleoplasm, chromatin and nucleolus

Function: storage of genetic information, controls metabolic functioning and structural characteristics of the cell.

NUCLEUS


Ribosomes

Composition: protein and RNA in two subunits

Function: Protein synthesis

RIBOSOMES


Endoplasmic reticulum

Composition: membranous saccules and canals

Function: synthesis and /or modification of proteins and other substances, and transport by vesicle formation

ENDOPLASMIC RETICULUM


Golgi apparatus

Composition: stack of membranous saccules

Function: Processing, packaging, and distribution of molecules

GOLGI APPARATUS


Vacuole and vesicle

Composition: membranous sac

Function: storage and transport substances

VACUOLE AND VESICLE


Lysosome

Composition: membranous vesicle containing digestive enzymes

Function: intracellular digestion

LYSOSOME


Mitochondrion

Composition: inner membrane (cristae) within outer membrane

Function: cellular respiration

MITOCHONDRION


Cytoskeleton

Composition: microtubles, actin filaments

Function: shape of the cell and movement of its parts.

CYTOSKELETON


Structure of the cytoskeleton

STRUCTURE OF THE CYTOSKELETON


Cilia and flagella

Composition: 9 + 2 pattern of microtubules

Function: movement of cell

CILIA AND FLAGELLA


Centriole

Composition: 9 + 0 pattern of microtubules

Function: formation of basal bodies

CENTRIOLE


Chromosome

CHROMOSOME

Chromosomes are rod-shaped structures made of DNA and proteins.


Chromosome1

Chromatid- the strand of a chromosome that becomes visible during meiosis or mitosis.

Chromatin – the less tightly coiled DNA-protein complex

Centromere – the region of the chromosome that holds the two sister chromatids together during mitosis.

CHROMOSOME


Sex chromosomes autosomes

Sex chromosomes are chromosomes that determine the sex of an organism, and they may also carry genes for other characteristics.

In humans, sex chromosomes are either X or Y.

XX for female

XY for male

The autosomes are all the other chromosomes in an organism except for sex chromosomes.

In humans two of the 46 are sex chromosomes, and the remaining 44 chromosomes are autosomes.

SEX CHROMOSOMES & AUTOSOMES


Human karyotype

HUMAN KARYOTYPE


Histone and non histone

The DNA in eukaryotic cells wraps tightly around proteins called histones.

Histones help maintain the shape of the chromosomes and aid in the tight packaging of DNA.

Nonhistone proteins are generally involved in controlling the activity of specific regions of the DNA

HISTONE AND NON-HISTONE


Cell cycle

CELL CYCLE

The cell cycle is an orderly set of stages that take place between the time a cell divides and the time the resulting daughter cells also divide.


Cell cycle stages

Interphase

-the cell carries on its regular activities.

The three stages:

G1 phase

S phase

G2 phase.

Mitotic Stage

Stages of mitosis:

karyokinesis (division of the nucleus)

cytokinesis (division of the cytoplasm).

CELL CYCLE STAGES


Dna replication

STAGES:

The old (parental) DNA strands unwind and “upzip”

New complementary nucleotides pair with the nucleotides in the old strands. A pairs with T and C pairs with G.

The enzyme DNA polymerase joins the new nucleotides forming new (daughter) complementary strands.

When replication is complete, the two double helix molecules are identical.

DNA REPLICATION


Protein synthesis

PROTEIN SYNTHESIS

Is the formation of proteins by using information contained in DNA and carried by mRNA


Protein synthesis1

TRANSCRIPTION-

is the process of forming a nucleic acid by using another molecule as a template; particularly the process of synthesizing RNA by using one strand of a DNA molecule as a template.

TRANSLATION-

refers to the portion of protein synthesis that takes place at ribosomes and that uses the codons in mRNA molecules to specify the sequence of amino acids in polypeptide chains.

PROTEIN SYNTHESIS


Control of cell division

CONTROL OF CELL DIVISION

In eukaryotes, proteins regulate the progress of cell division at certain checkpoints.


Cell growth checkpoint

1. Cell Growth Checkpoint.

Proteins at this checkpoint control whether the cell will divide.

Hint: if the cell is healthy and has grown to a suitable size during G1 phase, protein will initiate DNA synthesis (S phase). If conditions are not favorable for DNA synthesis, the cell cycle will stop at this point.

CELL GROWTH CHECKPOINT


Dna synthesis checkpoint

2. DNA Synthesis (G2) checkpoint.

DNA repair enzymes check the results of DNA replication. If this checkpoint is passed, proteins will signal the cell to begin the molecular processes that will allow the cell to divide mitotically.

DNA SYNTHESIS CHECKPOINT


Mitosis checkpoint

3. Mitosis checkpoint.

If a cell passes this checkpoint, proteins signal the cell to exit mitosis. The cell enters into the G1 phase, the major growth phase of the cell cycle, once again.

MITOSIS CHECKPOINT


Prokaryotic cell division

PROKARYOTIC CELL DIVISION

Most prokaryotes reproduce by binary fission, in which two identical cells are produced from one cell.


Eukaryotic cell division

EUKARYOTIC CELL DIVISION

In eukaryotic cell division, both the cytoplasm and the nucleus divide. There are two types of cell division in eukaryotes – mitosis and meiosis.


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