Voice of the Genome Flashcards
Approx. how many genes does a human have?
20K - 25K
(thousands)
What is the function of genes?
They provide the instruction manual to build the organism from the unspecialised cells to the specialised which make up the systems, etc.
What are prokaryotic cells?
give example
E.g., bacteria, cyanobacteria
- cell wall
- no nuclei
- DNA floats in cytoplasm
- no other membrane bound organelles
Describe eukaryotic cells?
membrane bound organelles
nucleus
don’t all have a cell wall (have a membrane instead)
What is the function of the mitochondria
the site of later stage respiration
what do centrioles do?
every cell as a pair of centrioles
these are hollow protein cylinders that assist in the formation of the spindles in cellular division as well as transport within the cell
what do lysosomes do?
spherical sacks
break down unwanted structures in the cell
also help to destroy old cells
what is the functiono of the Golgi complex?
Modify proteins and packs them up in vesicles for transport
Function of smooth endoplasmic reticulum?
Makes lipids and steroids
what does the membrane do?
partially permeable barrier allowing some nutrients and gases in/out
what do ribsomes do?
Float around the cytoplasm synthesising proteins
Rough endoplasmic reticulum
rough - b/c ribosomes attacked on the membrane
proteins are made on the ribosomes to be transported through the ER to other parts of the cell
What’s the nucleolus?
Dense body within the nucleus where ribosomes are made
What is the function of the nucleus?
Contains the cell’s chromosomes and nucleolus
Chromosomes made of DNA contain gense that control protein synthesis
Describe the process of proteins out of a cell
DNA transcribed into mRNA
- mRNA leaves nucleus
- Protein made on ribosomes enter rough endoplasmic reticulum
- proten moves through the ER forming 3D shape
- proteins packaged in vesicles off the ER
- the vesicles fuse to form flattened sacs of the Golgi complex
- proteins are modified within the Golgi
- vesicles pinched off Golgi
- vesicles fuse with cell surface and release protein out of cell
What are gametes?
The sex cells - sperm, ova
What does an ovum contain?
protein and lipid food reserves for the developing embryo
it is surrounded by the zona pellucida (jelly-like covering)
Explain fertilisation of sperm and ova
- Sperm use flaggelum to swim to ovum powered by their mitochondria
- Sperm are attracted by the ovum’s chemicals it releases
- On oval contact: the acrosome in the head of a sperm swells and releases digestive enzymes to break down the ovum’s zona pellicida (the acrosome reaction)
- Once the sperm fuses and penetrates the ovum, the zona pellucida then thickens to prevent other wannabee babies - ‘corticol reaction’
What are homologous chromosomes?
A pair of chromosomes with the same gene sequence, loci, chromosomal length, and centromere location.
What is special about gametes?
They contain only 1/2 the normal full set of chromosomes
(23 in humans)
AKA - haploid, rather than diploid
How are gametes formed?
During meiosis, occuring in ovaries and testes
In meiosis cell division there is
independent assortment
only one chromosome from each pair ends up in a gamete
this is a source of genetic variation, a random process
b/c either chromosome could be in the gamete
hence in fertilisation the possible combination of chromosomes is large (three homologous pairs could form 23 combinations)
and crossing over
when homologous chromosomes join together as pairs, all four chromatids come into contact
at the contact points, the chromatids break (at a chiasma, cross) and rejoin exchanging sections of DNA creating a wide range of variation
What is genetic linkage?
The idea that certain characteristics tend to be inherited together as the genes have a locus on the same chromosome and will hence tend to be passed on as a pair to the same gamete
e.g., hair colour and eye colour
What are sex-linked conditions?
genetic conditions passed on via the two sex chromosomes
(XX female, XY male)
E.g., red-green colour and haemophilia blindness afffects mainly men
How is red-green colour blindness passed on?
The gene loci for the three colour cone cells in the eye are found on the X sex chromosome
During meiosis, there can be a mutation of one of the cone pigment genes
E.G.> Emily is heterozygous for colour blindness, XNXn
- XN= X chromosome with a normal allele for cone pigment
- Xn= X chomosome with a mutant allele for cone pigment
- Emily has normal vision, but mates with Greg who has XNY; (Y does not have a place for the cone pigment, so is empty)
- PUNNET SQUARE analysis
- Emily offers: XNXn
- Greg offers: XNY
- or (XNXn)(XNY) = XNXN; XNXn; XNY, XnY
- Leaving us with 50% chance of full vision in offspring
- 25% chance of a boy with full colour vision (XNY) and
- 25% chance of a boy who is colour blind (XnY)
What is the process of plant fertilisation?
Ova are produced in an ovary but only one of the four nuclei at the end of meiosis forms an ovum
Inside the anther, cells divide to produce pollen grains containing male gamete nuclei
In male plants, the four haploid cells produced in meiosis undergo another mitosis division in which each nucleus divides to give two haploid nuclei in a pollen grain
Fertilisation takes place in the ovule - pollen germinate on the style and grown down towards the ovary, a process controlled by one of its haploid cells, while the other haploid nucleus divides to form two new haploid nuclei that move down the pollen tube
The tube grows through a microscopic pore into the embryo sac in the ovule, and the two male gametes enter the sac
1 male gamete fuses with the egg cell -> diploid zygote forms
1 male gamete fuses with two nuclei in the embyronic sac called polar nuclei to form a triploid cell, which then divides to form endosperm (the seed’s storage tissue)
Phew.
