3.1 - In the beginning Flashcards
What is the function of the mitochondria?
- site of later stages of aerobic respriation
- inner of its 2 membranes are folded to form finger-like projections called cristae
What is the nucleus contain?
*don’t say just DNA or genetic info
- contains chromosomes & nucleolus
What are chromsomes made up of?
DNA, contains genes that control synthesis of proteins
What is the chromosomes and nucleolus enclosed in? What is it made up of?
envelope made up of 2 membranes pierced by pores
What is the function of the nucleolus?
dense body within the nucleus where ribosomes are made
What is the rough endoplasmic reticulum?
- system of interconnected membrane-bound, flattened sacs
What is attached to the outer surface of RER?
ribosomes
What is the function of the rough endoplasmic reticulum?
proteins made on attached ribosomes & are transported through the ER to other parts of cell
What is the function of the ribsomes?
site of protein sythesis
What are ribosomes made of?
made of RNA & protein, they are found free in the cytoplasm or attached rough ER
What is cell surface membrane/plasma membrane? What is its function?
phospholipid bilayer containing proteins & other molecules forming a partially permeable barrier
What is the smooth endoplasmic reticulum?
- like rough ER, but without attached ribsomes
- makes lipids & steroids
What is the golgi apparatus? What is its function?
- stacks of flattened, membrane-bound sacs formed by fusion of vesicles from ER
- modifies proteins and packages them in vesicles for transport
What are the lysosome?
spherical sacs containg digestive enzymes & bound by a single membrane
What is the function of the lysosome?
- involved in breakdown of unwanted structures in cell & in destruction of whole cells, when old cell are to be replaced
What is a specialised lysosome?
acrosome
What are centrioles?
hollow cylinders made up of a ring of 9 nine protein microtubules
What is the function of centrioles?
involved in formation of spindle during nuclear division & in transport with cytoplasm
Which structures are always present in an eukaryotic cell?
- nucleus
- mitochondria
- chloroplasts (plant cells)
- endoplasmic reticulum
- ribosomes
- cytoskeleton
- chromosomes
- cell wall (plant cells)
Which 2 structures are sometimes present in an eukaryotic cell?
cilia & flagella
Which structures are always present in a prokaryotic cell?
- ribosomes
- cell wall
- chromosomes
Which structure is sometimes present in prokaryotic cells?
flagella
What happens in protein trafficking? (9 steps)
- Transcription (in nucleus), of DNA to mRNA
- mRNA leaves nucleus
- proteins made on ribosomes enter through rough ER
- proteins move through ER, adopting tertiary structure en route
- vesicles pinched off rough ER contain protein
- vesicles from rough ER fuse to form the flattened sacs of the Golgi apparatus
- proteins are modified within the Golgi apparatus
- vesicles pinched off the Golgi apparatus contain the modified proteins
- vesicles fused with the cell surface membrane releasing proteins (such as extracellular enzymes & these extracellular enzymes will undergo exocytosis)
What is protein trafficking?
movement of proteins in a cell
What are the 4 stages of mitosis?
- prophase
- metaphase
- anaphase
- telophase
What happens in prophase?
- chromosomes condense & become visible as 2 strands
- centrioles move around nuclear envelope & position themselves at opposite sides of cell
- 2 poles of the spindle are formed & are involved in organisation of spindle fibres
- nuclear envelope is broken down
What is widest part of the spindle called?
equator
What happens during metaphase?
- chromsomes’ centromeres attach to spindle fibres at equator
What happens during anaphase?
- centromeres split
- spindle fibres shorten, pulling 2 halves of each centromere in opposite directions
- one chromatid of each chromosome to each of the poles
- spindle breaks down
What happens in telophase?
- chromosomes unravel & nuclear envelope reforms, so 2 sets of genetic information become enclosed in separate nuclei
What are the steps of the acrosome reaction?
- sperm reaches egg cell & binds to zona pellucida
- Acrosome swells & fuses with sperm cell surface membrane
- Digestive enzymes in acrosome released
- Enzymes digest a tunnel through follice & zona pellucida, so sperm can reach plasma membrane of egg cell
- plasma membrane of sperm cell & egg cell fuse
- sperm releases its nucleus into egg cell cytosplasm
- nuclei of sperm & egg fuse
Define fertilisation.
fusion of sperm nuclei & egg nuclei
How many chromosomes does a zygote contain?
46 (full no.)
What is formed after fertilisation?
zygote
What are the adaptions of an egg cell? How does this mean they can carry out their function?
cytoplasm - contains nutrients for embryo growth
lysosomes - thickens zona pellucida to prevent sperm entry
follicle cells - form protective coating around egg cell
zona pellucida - releases chemicals to attract sperm
cell surface membrane - allows sperm to enter cell
Do sex cells contain one copy or two copies of chromosomes?
one copy
What the type of gametes called before fertilisation?
haploid gametes
What are the 4 adaptations of a sperm cell? How does this it can carry out its functions?
flagellum - swim to egg cell
streamlined shape - faster swimming
body contains lots of mitochondria - provides ATP for movement
head contains acrosome - filled with digestive enzymes to break down egg’s ZP & allow sperm to reach egg cell membrane
What does the cortical reaction prevent?
multiple sperm cells from fertilising egg
What is the process of the cortical reaction?
- Fusion of sperm cell & egg cell cell surface membrane
- Cortical granules release their contents (by exocytosis) into the zona pellucida
- These contents react with the zona pellucia causing it to harden which prevents other sperm cells from entering
- Sperm & egg cell nuclei then fuse
Does the cortical reaction occur before or after the acrosome reaction?
after
What is meiosis?
cell division that results in productions of 4 haploid nuclei
What does meiosis produce?
gametes
What are the 2 divisions of meiosi called?
Meiosis I & Meiosis II
What does meiosis create?
genetic variation among offspring
What happens in Meiosis I?
homologous chromosomes pair up as bivalents
What happens in Meiosis II?
chromatids separate & haploid gametes are formed
What happens in the whole of meiosis?
- Before division begins, both chromosomes replicate (DNA replication). 46 chromosomes are presents in one diploid parent cell
- after replication each chromosomes is made of 2 strands of DNA called 2 chromatids. 23 chromosomes are present.
- Meiosis 1 - Homologous chromosomes pair up as bivalents and then separate
- Meiosis 2 - Second division (similar to mitosis). Chromatids separate and haploid gametes are formed.
What are the 2 ways that crossing over can lead to genetic variation?
- crossing over
- independent assortment
When does crossing over occur?
meiosis 1
What happens during crossing over?
- homologous chromosomes come together as pairs & all 4 chromatids come into contact
- at these contact points, chromatids break & region exchanging sections of DNA between non-sister chromatids
What is the point when chromatids break called?
chiasmata
How does crossing over lead to genetic variation?
many chiasmata nay form anywhere along length of chromsome, leading -> chromosomes containing new combinations of alleels from both parents
Does crossing over occur between sex chromosomes occur?
no
When does independent assortment occur?
occurs during meiosis 1
What happens during independent assortment?
- each gamete ends up w only one of homologous pairs of chromosomes
- independent assortment of chromosomes as they line up during meiosis is random & either chromosome from each pair could be in either gamete
What does independent assortment mean for the gametes?
gametes can end up with many diff. combinations of maternal or paternal chromosomes
Why is genetic variation important?
enables some individuals to adapt to environment while maintaining survival of population
Other than independent assortment & crossing over, what else can lead to varition?
random fertilisation
What is random fertilisation?
where it is completely as to which sperm will fertilise egg
Where does meiosis occur?
in reproductive organs
What is a chromatid?
identical half of the copied chromosome
What are centromeres?
region where 2 chromatids are joined at
What is meant by the term polygenic?
- a characteristic showing continuous variation
- caused by multiple genes at different loci
