Bio HL1 2.2 Cell Structure

smallest unit of life

cells

cells come from

pre existing cells

organelles

discrete structures that adapted to perform unique functions

organelles are efficient because

they are specialized for limited functions

organelles with no membrane

ribosomes, centrioles

organelles with a single membrane

rER, golgi apparatus, vesicles

organelles with double membranes

nucleus, mitochondria, chloroplast

structures that are considered non-organelles

cell wall (thought as extracellular)
cytoskeleton (not discrete enough, though microtubules are organelles)

cytoplasm (many different structures with unique functions)

universal structures (common to all cells in living organisms)

plasma membrane, DNA, ribosomes

plasma membrane structure

phospholopid bilayer with embedded proteins and cholesterol

plasma membrane function

semi-permeable barrier that separates internal/external ENV, controls entry and exit of substances

DNA structure

double helix made of nucleotides

DNA function

contains instruction for cells to carry out functions, specifically proteins

ribosome structure/size

two subunits (large and small) with rRNA and proteins; 70S in prokaryotes and 80S in eukaryotes

ribosome function

protein synthesis, free ribosomes make proteins to be used in cytosol while bound ribosomes make secretory proteins; they are structurally identical and interchangeable

prokaryote characteristics

no nucleus, peptidoglycan cell wall (protects cell and maintains shape), cytoplasm that is an internal fluid containing enzymes, naked DNA in a loop (nucleoid), DNA lacks histone proteins and is circular, plasmids are extra circular DNA with additional information

prokaryote membrane characteristics

mesosomes (infoldings) for sites for metabolic processes like cellular respiration

gram positive eubacteria stains purple due to

peptidoglycan that retains violet dye, including Bacillus and Staphylococcus

prokaryotes vary in

structure regarding cell wall composition, plasmid presence, flagella, or capsule

E

cell wall

C

nucleoid

F

plasma membrane

D

flagella

size ratio

2:1

shape

rod-shaped

eukaryotic cells have many compartments because

optimal concentrations of enzymes and substrates are held, with incompatible processes being seperated

lysosomes and phagocytic vacuoles with ______ enzymes are kept ________.

hydrolytic; in organelles

organelles and contents around the cell are moved by

the cytoplasm

nucleus structure

double-membraned nuclear envelope with pores; nucleolus region that performs ribosome synthesis

nucleus function

stores genetic information as DNA wrapped in histones

benefits of double nuclear membrane

transportation in and out of the nucleus: proteins made in cytoplasm are needed in nucleus for CHR (histones) and gene regulation (spliceosomes)

the molecules made in nucleus need to be exported to cytoplasm (mRNA, tRNA, ribosomes), this requires pores wider than channel proteins

the double membrane forms larger pores by

connecting innermost and outermost membranes to form an end

how do nuclear pores control what passes through

rims of nuclear pores are lined with proteins that control this

to perform mitosis and meiosis, the nuclear membrane breaks down so

CHR can move to opposite poles

the entire structure breaks down by

budding off vesicles that later fuse together to form new nuclear membranes

rough endoplasmic reticulum structure

consists of cisternae (flattened membrane sacs) with 80S ribosomes attached

rough endoplasmic reticulum function

folds and packages secretory proteins, with vesicles budding off and moving to Golgi

smooth endoplasmic reticulum structure

tubular membranes with no ribosomes attached

smooth endoplasmic reticulum function

makes lipids (phospholipids & hormones), detoxifies drugs (liver), and stores calcium ions (muscles)

golgi apparatus structure

consists of cisternae (flattened membrane sacs)

golgi apparatus function

adds carbohydrates (glycoproteins), phosphate or sulfate groups

different sacs are responsible for different modifications

types of proteins that pass through the golgi

secretory proteins, cell membrane proteins, lysosomal proteins

once processed in the golgi, proteins are moved to their destinations via

vesicles

vesicles move from ___ side to ____ side

cis; trans

vesicle transport model

cisternae remain static, vesicles move proteins between them

cisternal maturation model

rER vesicles coalesce to form new cisternae on cis side, which then mature and move to trans side where they are broken down to vesicles

lysosomes are solely in

animal cells

lysosome structure

membrane sacs filled with hydrolytic enzymes from Golgi

lysosome function

digests food, organelles, and sometimes whole cells

mitochondria structure

double membrane; smooth outer part with inner section containing cristae (increases surface area); mitochondrial matrix in center; contains own DNA and ribosomes and makes own proteins

mitochondria function

makes ATP through cellular respiration

vacuoles and vesicle structure

membrane sacs filled with fluid

vacuoles and vesicle function

transports and stores materials

vesicles in animal cells

temporary

vacuoles in plant cells

typically large central vacuoles that store water, pigments, poison, and maintain hydrostatic pressure

some unicellular organisms use vacuoles to

expel water (Paramecium)

vesicles move contents within; membrane or proteins that

make up the vesicle

as the cell grows, ____ needs to increase

plasma membrane

phospholipids are made by sER and inserted into

the rER membrane

ribosomes on rER further make proteins

that are inserted into the membrane

clathrin

three-legged protein that positions itself on the budding end of membrane before a vesicle forms

adjacent clathrins form

a lattice by linking together, pulling membrane into a bud

the bud is ____ by another protein, the vesicle detaches and forms a ____ with clathrin around it, and clathrin then dissociates

cleaved; sphere

cytoskeleton (also in prokaryotes) structure

microtubules (largest) made of tubilin and microfilaments (smallest) made of actin

cytoskeleton (also in prokaryotes) function

microtubules are found in mitotic spindle and cilia/flagella

microfilaments perform cytoplasmic streaming, muscle contraction, and help animal cells maintain their shape

both move organelles within the cell

centrosome (only in animal cells) structure

contains paired centrioles, each made of 9 triplet microtubules

centrosome (only in animal cells) function

microtubule-organizing centers that make spindle fibers during cell divison

chloroplast (only in plant cells) structure

double membrane, stacks of thylakoid inside granum, chlorophyll acts as photosynthetic pigment

chloroplast (only in plant cells) function

photosynthesis: makes glucose, may contain starch grains

atypical cell structures

red blood cells, skeletal muscles, aseptate fungal hyphae, phloem sieve tube elements

red blood cell characteristics

no nuclei or mitochondria so cell can carry more hemoglobin, cannot replicate and instead is produced within bone marrow

skeletal muscles characteristics

cells fuse together to form long fibers, with a continuous plasma membrane and multiple nuclei

aseptate fungal hyphae characteristics

used for nutrient absorption and growth; nucleus divides repeatedly without cell division, some walls form without a nucleus

phloem sieve tube elements

transports sugars throughout plant, lacks nuclei and some organelles to maximize space and limit friction

ocular lens is

10x

objective lenses are

4x, 10x, 40x

when using magnification formula, units must be

the same

1cm

10mm

1mm

1,000 μm

1 μm

1,000 nm

electron microscopy utilizes

beams of e- focused by electromagnets, advantageous because it has a much higher magnification and resolution, allows visualization of ultrastructure (ribosomes) and viruses

freeze fracture

cell is frozen and split along lines of weakness; membrane interior is revealed by splitting lipid bilayer, 3D images of integral membrane proteins and distribution are provided

cryogenic electron microscopy (Cryo-EM)

rapid freezing of biological molecules to preserve structure without chemicals

cryogenic electron microscopy advantages

allows research on how proteins change structure, maintains molecules in near-native state, avoids consequences of staining/dehydration, enables visualization of macromolecules at a near atomic resolution

fluorescent stains in light microscopy

dyes that bind to specific cell structures and emit visible light when excited by certain wavelength; immunofluorescence tags antibodies with fluorescent markers

fluorescent stains in light microscopy advantages

increases contrast and allows visualization of specific organelles and antigens (proteins)

endosymbiosis

all eukaryotes evolved from a common unicellular ancestor that had a nucleus and reproduced sexually, mitochondria and chloroplasts evolved by endosymboisis, where a eukaryote engulfed a prokaryote and, rather than digesting, developed a symbiotic relationship. over time, the prokaryote lost some of its independence and became organelles

evidence of endosymbiosis

mitochondria and chloroplasts have:

their own DNA (circular and naked like prokaryotes)

own 70S ribosomes

replicate independently by binary fission (used in prokaryotes)

double membrane—outer may have been a vesicle