Cell Structure Flashcards
Two types of cells
- Eukaryotes - Cells with a nucleus and organelles
- Prokaryotes - Cells with no nucleus (bacteria)
Organelles
Self-contained structures inside cells. All have their own membranes
Nucleus
- Contains chromosomes (genes made of DNA which code for protein synthesis)
- Separated from the cytoplasm by a nuclear envelope and its continuous with Rough ER
- The envelope is made of a double membrane containing small holes called Nuclear Pores (100nm)
- Nuclear Pores allow the transport of mRNA in and out of the nucleus
- Nucleolus - makes ribosomal RNA (rRNA) and ribosomes
- Chromatin - protein (histone) + DNA
Endoplasmic Reticulum (ER)
- Its a series of tubes (membranes) running through the cytoplasm which distributes substances through the cell. There are 2 types:
- Rough ER - has ribosomes (join amino acids) - makes proteins. Found in cells that are making proteins for export (enzymes, hormones, structural proteins, antibodies)
- Smooth ER - no ribosomes attached, makes detoxifies cell poisons, numerous in the liver
- ER is abundant in secretory cells
- rER puts the proteins into shuttle vesicles to transport them to the Golgi Body
- Structure - stack of cisternae or flattened sacs
Golgi Apparatus/Body
- Proteins from rER to the Golgi body which modifies it: Adds on carbohydrate group = glycoprotein, Folds it up-Enzymes, makes lysosomes
- Secretory vesicles bud of Golgi body and fuse with the cell membrane releasing the glycoprotein outside the cell. This is called exocytosis
Lysosomes
-Lysosomes are made by the Golgi body (and rER)
-Contain enzymes
They are used for:
1) Intracellular digestion
2) Breaks down worn out organelles
3) Breaks down cell after its death (Autolysis)
4) Breaks down whole organism - metamorphosis - also enzymes are secreted for extracellular digestion
Mitochondria
- Site of respiration - releases energy so requires oxygen and glucose; produces carbon dioxide and water
- Makes ATP (Adenosine Triphosphate) from ADP (Adenosine Diphosphate)
- Double membrane and inner membrane folded - cristae provides large surface area for enzyme attachment
- More mitochondria in active cells i.e. muscle and liver
Why do Mitochondria have______?
- Ribosomes - to make the enzymes (proteins) for respiration
- DNA - contain the genetic code for protein - enzyme: to replicate themselves especially when the cell becomes more active
Ribosomes
-Smallest organelle (20nm) last to be sedimented in a centrifuge
-Found in both prokaryotic and eukaryotic cells (more)
-Site of protein synthesis - join amino acids together to form polypeptide
-Two types:
>70s in prokaryotic cells, mitochondria & chloroplast
>80s in eukaryotic cells
Microvilli
Finger like projections on cell surface increase surface area for absorption
Centriole - not in plants
Structure:
-a centriole is a small set of microtubules (9) arranged in at right angles to each other and located just outside the nucleus
Function:
-Forms the spindle during cell division
Vacuoles - not found in animal cells
- Structure - Fluid filled sac surrounded by single membrane called the tonoplast.
- Function - Contains cell sap, Provides support/turgor to cell
Chloroplasts - not found in animal cells
-Structure:
>Double membranes
>Inner membrane Is folded into flattened sacs thylakoids that are stacked into grana (one granum) - large surface area for chlorophyll attachment
>Chlorophyll - green pigment that absorbs light energy
>Lipid and starch grain - store products of photosynthesis
>DNA - to replicate themselves
>Ribosomes - to make enzymes for photosynthesis reaction
-Function:
>Absorbs light for photosynthesis - produce glucose and oxygen from CO2 and water
Cell Wall
-Structure:
>Made of cellulose (polysaccharides) in plant cells; that are held in microfibrils and embedded in pectin
-Function:
>Support - prevents cell bursting when turgid
>Transport - gaps between cellulose makes it fully permeable to substances
>Communication - between cells - have holes called pits that contain plasmodesmata
Plasmodesmata
- Structure - They are microscopic channels which traverse the cell walls of plant cells and some algal cells
- Functions - Allow transport and communication between cells
