TOPIC 3: VOICE OF THE GENOME

Description of nucleus

large organelle surrounded by a nuclear envelope which contains pores. the nucleus contains chromatin (which is made from DNA and proteins and a structure called the nucleolus.

Function of nucleus

Controls the cells activities by controlling the transcription of DNA. DNA contains instructions to make proteins. Pores allow substances to move between the nucleus and cytoplasm. The nucleolus makes ribosomes

Description of nucleolus

Dense body within the nucleus

Function of nucleolus

Makes ribosomes

Description of lysosome

a round organelle surrounded by a membrane with no clear internal structure

Function of lysosome

Contains digestive enzymes which are used to digest invading cells or break down worn components of the cell

Description of ribosome

a very small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum. It is made up of proteins and RNA. No membrane

Function of ribosome

Site where proteins are synthesised

Description of rough endoplasmic reticulum

a system of membrane bound flattened sacs. the surface is covered with ribosomes

Functions of rough endoplasmic reticum

folds and processes proteins that have been made at the ribosomes

Description of smooth endoplasmic reticulum

a system of membrane bound flattened sacs but with no ribosomes

Function of smooth endoplasmic reticulum

synthesises and processes lipids

Description of golgi apparatus

a group of fluid filled membrane bound flattened sacs. formed by the fusion of vesicles from the ER

Function of golgi apparatus

it processes and packages new lipids and proteins. it also makes lysosomes

Description of mitochondria

Double membrane- inner one is folded to form a structure called cristae. inside is the matrix which contains enzymes involved in respiration

Function of mitochondria

site of aerobic respiration, where ATP is produced. found in large numbers in cells that are very active and require a lot of energy.

Description of centriole

small hollow cylinders made of microtubules. found in animal cells but only some plant cells

Function of centriole

involved with the separation of chromosomes during cell division

What type of proteins do ribosomes make

Ribosomes on the rER make proteins that are excreted or attached to the cell membrane. Free ribosomes in the cytoplasm make proteins that stay in the cytoplasm.

What happens once the new proteins are made

They enter into the rER and are folded and processed. Then they are transported to the golgi apparatus in vesicles. The vesicles fuse to form the flattened sacs of the golgi and the golgi further processes the proteins. The proteins enter more vesicles and are transported around the cell

Cytoplasm in prokaryotic cell

no membrane bound organelles and has smaller ribosomes than in eurkaryotic cell

Flagellum

long hair like structure that rotates to make the prokaryotic cell move. not all prokaryotes have a flagellum and some have more than one

Circular DNA

long coiled up strand of DNA that is not attached to any histone proteins

Plasmid

small loops of DNA that aren't part of the main circular DNA molecule. contain genes for things like antibiotic resistance

Mesosome

inward folds in the plasma membrane.

Capsule

made up of secreted slime. helps protect bacteria from attack by cells of the immune system and prevents dehydration

Pili

short hair like structure. helps prokaryotes stick to other cells and can be used to transfer genetic material between cells

Cell wall in prokaryotes

support the cell and prevent it from changing shape. made of murein glycoprotein

Plasma membrane (prokaryotes)

mainly made of lipids and proteins. controls the movement of substances into and out of the cell

tissue

group of similar cells that are specially adapted to work together to carry out a particular function

organ

group of different tissues that work together to perform a particular function

organ system

Group of organs that work together to perform a particular function

What kind of cell does mitosis produce

genetically identical daughter cells

what is mitosis needed for

growth, repairing damaged tissues and for asexual reproduction

What does the cell cycle consist of

Interphase which is a period of cell growth and DNA replication (G1, S and G2) then Mitosis

What happens during Interphase

Gap phase 1 - cell grows and new organelles and proteins are made. Gap phase 2 - cell keeps growing and proteins needed for cell division are made. ATP content is increased. Synthesis - cell replicates its DNA ready to divide by mitosis

The order of stages in mitosis

prophase, metaphase, anaphase and telophase

Prophase

chromosomes condense, becoming shorter and thicker, each chromosome is visible as 2 strands called chromatids. centrioles start moving to opposite ends of the cell, forming a network of protein fibres called a spindle. nuclear envelope breaks down and the chromosomes lie free in the cytoplasm

Metaphase

chromosomes, each with 2 chromatids line up along the middle of the cell and become attched to the spindle fibres at their equator by their centromeres.

Anaphase

centromeres divide, separating each pair of sister chromatids. the spindles contract, pulling chromatids to opposite poles of the spindle, centromere first

Telophase

chromatids reach the opposite poles on the spindle. they uncoil and become long and thin and are called chromosomes again. a nuclear envelope forms around each group of chromosomes so there are 2 nuclei. The cytoplasm divides and there are now 2 genetically identical daughter cells.

How does mitosis ensure genetic consistency

DNA replication before mitosis. The arrangement of chromosomes on the spindle and the separation of chromosomes to the pole

What are gametes

the male and female sex cells found in all organisms that reproduce sexually

Why is it important that gametes only have one set of chromosomes

during fertilsation a zygote is created with the full number of chromosomes

What are the adaptations of an egg cell

zona pellucida which is a jelly like coating that is a protective layer the sperm has to penetrate. follicle cells are a protective coating. lipid droplets are a food store for developing embryo.

What are the adaptations of a sperm cell

Lots of mitochondria to provide energy for tail movement. Acrosome which contains digestive enzymes used to break down the zona pellucida of the egg so sperm can penetrate. flagellum allows sperm to swim towards the egg cell

What is the acrosome reaction and what triggers it

When the sperm reaches the egg and makes contact with the zona pellucida. Chemicals are released from the follical cells. The acrosome swells and fuses with the sperm cell membrane. Digestive enzymes are released and they digest the follical cells and zona pellucida

What happens when the sperm moves through to the cell membrane

the sperm head fuses with the egg cell membrane and this triggers the cortical reaction. The egg cell releases enzymes from cortical granules into the space between the cell membrane and zona pellucida.

What do the enzymes from cortical granules do

make the zona pellucida thicken so it is impenetrable to other sperm. this ensures only one sperm fertilises the egg cell

Fertilsation

when the nuclei of the egg and sperm cells fuse to form a a zygote

Haploid nucleus definition

one set of chromosomes. half the number of chromosomes found in a normal body cell. contains one chromosome from each homologos pair, type of nucleus found in gametes

Diploid

two sets of chromosomes

Meiosis

type of cell division that produces gametes

Without meiosis, what would happen

there would be double the number of chromosomes when the gametes fuse

genetic variation

differences that exist between individual's genetic material

How does meiosis produce cells that are genetically different

through crossing over of chromatids and independent assortment of chromosomes

Crossing over process

during first devision in meiosis, the homologous pairs of chromosomes come together and pair up. two of the chromatids in each homologous pair twist around eachother. the twisted bits break off their original chromatid and rejoin on the other chromarid, recombining their genetic material, exchanging sections of DNA.

chiasma

the point where chromatids break

How does crossing over increase genetic variation

each four new cells formed from meiosis contains chromatids with different combinations of alleles

Independent assortment

the random distribution of genes with loci on different chromosomes in the gametes. When gametes are produced, different combinations of the maternal and paternal chromosomes go into each cell. only one chromosome from each pair ends up in each gamete

locus

position of a gene on a chromosome

Linked genes

have their loci on the same chromosome and so stay togethr during independent assortment and are passed on to offspring together

How can linked genes be separated

by crossing over

What makes two genes more closely linked

having their loci closer together on the same chromosome

sex linked

locus of the gene is on a sex chromosome

Why are most genes on the X chromosome

the Y chromosome is smaller than X so it carries fewer genes

Why are males more likely to show recessive phenotypes than females

They only have one X chromosome, so they often only have one allele for sex linked genes. As they only have one copy, they express the characteristic of this allele even if it is recessive

Examples of X linked disorders

colour blindness and haemophilia

What are stem cells

unspecialised cells that can develop into other types of cells

What is differentiation

the process by which a cell becomes specialised

What is potency

the ability of stem cells to differentiate into specialised cells

What is totipotency

the ability of a stem cell to produce all cell types, including all the specialised cells in an organism and extraembryonic cells

What is pluripotency

the ability of a stem cell to produce all the specialised cells in an organism but not extraembryonic cells because the genes for these cell types have become inactivated

Where are totipotent stem cells present

in the first few cell divisions of an embryo

What kind of potency do adult stem cells have

multipotency.

Why do stem cells become specialised

different genes in their DNA become active and get expressed

How do stem cells become specialised

When there is a chemical stimulus, some genes are activated and others are inactivated. Transcription occurs at the active genes. mRNA from the active genes is translated on ribosomes to produce proteins. Protein modifies the cell and determines its structure and functions. Changes to the cell produced by these proteins cause the cell to become specialised.

How does inbreeding lead to genetic defects

There is a small gene pool which increases the chance of homozygous recessive genotypes for genetic defects

Explain the importance of meiosis in gametes production

to half the chromosome number producing a haploid nucleus, so at fertilisation the diploid number of chromosomes is restored. it allows genetic variation through independent assortment and crossing over.

What are the advantages of patient stem cells over donor stem cells

Less risk of infection, no risk of rejection, no need to take immunosuppressant drugs as it is geneticall identical to the patients cells

What is polygenic inheritance

There are multiple genes for a single characteristic on more than one locus. These genes interact. Usually show continuous variation

Why are there regulatory authorities for human embryo research

decide on max age of embryo allowed for research, stopping of cloning, judging what is acceptable by following codes of practice, checking the source of the stem cell is acceptable

Why does asexual reproduction lead to low genetic diversity

Low genetic diversity means there are few different alleles in the gene pool. Asexual reproduction leads to all offspring being genetically identical. No meiosis.

Why are organs more complex than tissues

Organs are made up of tissues. Organs are made up of many different cell types. Organs can have more than one function

How do epigentic changes affect the functioning of the genome

Methylation of DNA base therefore the expression of the gene is changed. If histones are modified, this may affect binding of other proteins to DNA because DNA is wrapped around histones. Therefore genes may become activated or repressed

What is gene expression controlled by

altering the rate of transcription of genes

What are transcription factors

proteins that bind to DNA and activate or deactivate genes increasing or decreasing the rate of transcription

What are activators and how do they work

Transcription factors that increase the rate of transcription by helping the RNA polymerase bind to DNA and begin transcription

What are repressors and how do they work

Transcription factors that decrease the rate of transcription by preventing the RNA polymerase from binding and so stopping transcription

Where do transcription factors bind in eukaryotes

specific DNA sites near the start of their target genes

Where do transcription factors bind in prokaryotes

operons

What is an operon

a section of DNA that contains a cluster of structural genes that are transcribed together aswell as control elements and sometimes a regulatory gene

What are structural genes

useful proteins

What are control elements

A promoter region which is the DNA sequence that RNA polymerase binds to and an operator site which is the DNA sequence that transcription factors bind

What does the regulatory gene code for

an activator or repressor

What is E.coli

a bacterium that respires glucose but can use lactose if glucose isnt available

What does B galactosidase do

breaks down lactose into glucose and galactose

What happens when lactose is not present

the regulatory gene (lacl) makes the lac repressor molecule which then binds to the operator site on the DNA. This blocks transcription as RNA cannot bind to the promoter

What happens when lactose is present

lactose binds to the repressor changing its shape so it cannot bind to the operator site anymore. RNA polymerase can bind to the promoter region so B galactosidase gene is expressed

How can stem cells be used in medicine

To replace damaged tissues