2.1.1. Cell structure

what things must be ensured for biological drawings

Biological drawings are line drawings that focus on particular features of a specimen:

• Drawings should be accurate, reflecting the proportions of the observed structures as closely as possible.

• drawing is centrally placed on the page, with sufficient space for labels.

• Use as much of the paper as possible.

• Include a title / heading.

• Using a sharp pencil, draw using continuous lines with no shading, on plain paper.

• Draw clearly defined structures.

• Include a scale bar.

• State the magnification used.

• Label lines should be drawn with a ruler and should not overlap each other.

anatomy of nucleus

The nucleus is usually the largest organelle

1. containing the cell’s genetic material (DNA).

2. The nucleus controls cell activities, including growth and metabolism, by regulating gene expression and protein synthesis.

3. It contains chromatin, consisting of linear DNA wrapped around histone proteins, which condenses to form chromosomes during cell division.

4. The nucleolus is a dense, spherical region within the nucleus that synthesises ribosomal RNA (rRNA) and assembles ribosomal subunits.

anatomy of nuclear membrane

The nuclear envelope is a double membrane

1. surrounding the nucleus

2. containing nuclear pores

3. that regulate the movement of substances such as mRNA and proteins between the nucleus and cytoplasm.

anatomy of RER, function

1. The rough endoplasmic reticulum (RER) is a network of interconnected, flattened membrane sacs

2. called cisternae,

3. which are continuous with the nuclear envelope.

4. Ribosomes attached to its surface give it a rough appearance.

The RER is the site of synthesis and transport of proteins destined for secretion or insertion into cell membranes.

1. Proteins enter the cisternae,

2. where they are folded and modified

3. before being transported to the Golgi apparatus

4. for further processing.

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anatomy of SER

The smooth endoplasmic reticulum (SER) is a network of membranous tubules and sacs which extends throughout the cytoplasm.

It is similar in structure to the rough endoplasmic reticulum, but lacks attached ribosomes and therefore appears smooth.

The SER is involved in the synthesis and transport of lipids, including phospholipids, cholesterol and steroid hormones.

anatomy of Golgi, function

1. The Golgi apparatus is a stack of flattened, single membrane–bound sacs called cisternae.

2. It modifies proteins and lipids received from the endoplasmic reticulum, for example, by adding carbohydrate chains.

3. These molecules are then sorted and packaged into vesicles

4. for transport to the cell surface

5. for exocytosis or to other organelles, such as lysosomes.

anatomy structure of ribosome

1. Ribosomes are small,

2. non–membrane–bound organelles made of ribosomal RNA (rRNA) and protein.

3. They are found free in the cytoplasm or attached to the rough endoplasmic reticulum and are the site of protein synthesis.

anatomy structure of mitochondria

1. Mitochondria are double membrane–bound organelles

2. that are the site of the later stages of aerobicrespiration and ATP production.

3. Cells with high metabolic activity, such as muscles and neurones, contain many mitochondria.

4. The inner membrane is folded into cristae, increasing the surface area for respiratory enzymes and electron carriers.

5. Mitochondria with more densely folded cristae have a greater capacity for aerobic respiration and ATP production.

6. The fluid-filled interior is called the matrix and contains enzymes, mitochondrial DNA and ribosomes.

structure anatomy of lysosome

1. Lysosomes are single membrane–bound vesicles

2. formed from the Golgi apparatus

3. that contain hydrolytic (digestive) enzymes, including lysozymes enzyme

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6. They digest ;

7. cellular debris

8. worn-out organelles

9. pathogens such as bacteria,

10. and also play a role in apoptosis (programmed cell death).

Lysosomes are particularly abundant in phagocytic cells such as macrophages and neutrophils.

antaobmy function of cell surface membrane

1. The cell–surface membrane, also called the plasma membrane, separates the cell’s contents from the environment surrounding the cell.

2. The partially or selectively permeable membrane controls the movement of substances

3. and is involved in cell signalling and recognition.

4. The membrane consists of a phospholipid bilayer

5. containing proteins, cholesterol and carbohydrate-containing molecules.

anatomy function of centrioles

1. Centrioles are small hollow cylinders

2. found in pairs in animal cells,

3. but absent from most plant and fungal cells.

4. Each centriole consists of a ring of nine microtubules formed from protein subunits.

Centrioles are involved in ;

1. spindle formation during nuclear division (mitosis and meiosis)

2. and help organise microtubules within the cytoplasm. (Microtubules are tiny protein tubes that form part of the cell's cytoskeleton.

   Centrioles help organise these tubes, which:

   • Help maintain cell structure.

   • Help move materials around inside the cell.

   • Help organise the cell during division.)

3. They also hold cilia and flagella in place;

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6. Cilia are tiny hair-like structures that move substances across the cell surface.

7. Flagella are longer, whip-like structures that help a cell move (e.g. sperm cells).

1. Centrioles are small cylindrical structures made of microtubules, found in the cytoplasm of animal cells

   
   

anatomy and function of chloroplast

1. is a double membrane–bound organelles found in plant

2. and algal cells that are the site of photosynthesis.

Chloroplasts contain;

1. flattened membrane sacs called thylakoids, which contain chlorophyll and

2. are stacked into grana

3. connected by lamellae.

4. These membranes are the site of the light-dependent reactions.

5. The fluid-filled stroma contains enzymes involved in the light-independent reactions.

6. Chloroplasts also contain circular DNA, ribosomes and starch grains for temporary carbohydrate storage.

anatomy and structure of cell wall

1. A cell wall is a freely permeable,

2. rigid outer layer

3. surrounding the cell–surface membrane in plants, algae and fungi.

4. Plant and algal cell walls are mainly made of cellulose

5. , whereas fungal cell walls are made of chitin.

The cell wall provides;

1. mechanical strength

2. and support,

3. helping maintain cell shape

4. and preventing the cell from bursting when water enters by osmosis.

5. The resistance of the cell wall to expansion allows turgor pressure to develop, making plant cells rigid.

flagella structure and anatomy

Flagella are;

1. long,

2. whip-like extensions of cells

3. formed from microtubules.

4. They can facilitate cell motility by propelling cells through their environment. Sperm cells and some bacterial cells are examples of cells that have flagella.

anatomy and structure of cilia

Cilia are

1. short,

2. hair-like extensions of cells,

3. composed of microtubules

4. and shorter than flagella.

5. Large groups of cilia can beat in coordinated waves

6. to move cells or organisms (e.g., Paramecium) or to movesubstances across cell surfaces (e.g., mucus in the respiratory tract).

In eukaryotic cells, protein production and secretion require the coordinated action of several organelles:

• mRNA is transcribed from DNA in the nucleus.

• It travels to ribosomes on the rough ER, where the protein is synthesised, powered by ATP generated in the mitochondria.

• The protein moves through the rough ER, folding into its 3D shape.

• They are packaged into transport vesicles that bud off and are carried to the Golgi apparatus via the cytoskeleton.

• Within the Golgi, proteins are modified (e.g., the addition of carbohydrate to form glycoproteins), then pinched off in secretory vesicles.

• These vesicles fuse with the cell-surface membrane, releasing the protein (such as extracellular enzymes) by exocytosis.

what is the cytoskeleton function

The cytoskeleton

1. helps maintain cell shape,

2. provides structural support,

3. facilitates intracellulart ransport,

4. and enables cell movement. I

5. forms the structural basis of cilia and flagella, allowing their movement.

what are microfilaments and function

Microfilaments are

1. thin protein filaments of the cytoskeleton made from actin.

2. They are involved in maintaining and changing cell shape

3. and play important roles in cell movement,;

4. muscle cell contraction, endocytosis, exocytosis, phagocytosis and cytokinesis.

microtubules anatomy function

Microtubules are

1. hollow protein filaments of the cytoskeleton

2. made from tubulin.

3. They providemechanical strength, helping maintain cell shape and resist compression.

4. Microtubules also act as tracks

5. for the movement of vesicles, organelles and molecules within the cell and help position organelles in the cytoplasm.

6. They are involved in spindle fibre formation during mitosis and meiosis.

what does prokaryote cells encounter, how do they differ form eukaryotes

Prokaryotes are unicellular organisms that include bacteria and archaea. They differ from eukaryotes in several ways:

• They lack membrane–bound organelles, including a nucleus.

• Their ribosomes are smaller.70s vs 80s

• They have a cell wall made of peptidoglycan.not chitin of cellulose

• Some possess flagella, which are structured differently from those of eukaryotes.

explain the genetic material in prokaryotes

Prokaryotic DNA consists of a single circular DNA molecule that is supercoiled, making it more compact.

It is found free in the cytoplasm and is not associated with histone proteins.

Prokaryotes may also contain small additional circular DNA molecules called plasmids.